Wind plans

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Wind plans

  1. 1. How to build aWIND TURBINEAxial flux alternator windmill plans8 foot and 4 foot diameter machines© Hugh Piggott -May 2003
  2. 2. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 2Hugh@scoraigwind.co.ukIntroductionBladesThese plans describe how to build two sizes of machine.The diameter of the larger wind-rotor is 8 feet [2.4 m].The smaller machine has 4 diameter [1.2 m].The diameter is the width of the circulararea swept by the blades.The energy produced by wind turbinesdepends on the swept area more than itdoes on the alternator maximum output.AlternatorThe plans describe how to build a permanent magnetalternator.The alternator can be wired for 12, 24 or 48-volt batterycharging. Essentially this choice only affects the size ofwire and the number of turns per coil. But the towerwiring for the 12-volt version will be much heavier thanthe others. And the stator for the small machine isdifferent in thickness.The alternator design is integrated into a simple tower-topmounting arrangement (called a yaw bearing). A tailvane faces the turbine into the wind. A built in rectifierconverts the electrical output to DC, ready to connect to abattery.Small wind turbines need low speed alternators. Lowspeed usually also means low power. The large machinealternator is exceptionally powerful because it contains 24large neodymium magnets. The power/speed curve for avery similar design is shown below. Maximum output isabout 500 watts under normal circumstances, but it iscapable of more than 1000 watts for short periods.The starting torque (force required to get it moving) isvery low because there are no gears, nor are there anylaminations in the alternator to produce magnetic drag.This means that the wind turbine can start in very lowwinds and produce useful power. Power losses are low inlow winds so the best possible battery charge is available.In higher winds the alternator holds down the speed of theblades, so the machine is quiet in operation, and theblades do not wear out. You can easily stop the windturbine by short-circuiting the output with a brakeswitch. These features make the wind turbine pleasant tolive with.BladesThe blades are carved from wood with hand tools. Youcan also use power tools if you prefer. Carved blades aregood for homebuilders because the process is pleasant andthe results are quick for a one-off product. Mouldedfibreglass blades are usually better for batch production.Wooden blades will last for many years.Furling systemThe plans include a description of how to construct afurling tail for the larger machine. This tail preventsoverload in high winds. This type of furling system hasbeen in use on Scoraig for decades and has passed the testof time.UnitsThis document caters for both American readers andEuropean/UK readers, so the dimensions are in bothinches and millimetres. The mm figures are in brackets[like this]. In some of the theory sections I use metricalone, because it makes the mathematics so much easier.In some cases, the metric dimensions will be directconversions of the English dimensions, but not always.The reasons are that different size magnets are used forthe metric design, metric wire sizes are different fromAWG, and some important physical dimensions arerounded off to make more sense in mm.The US version typically uses a standard GM hub(Citation, Cavalier, etc) with five studs and a bearing at theback. The bearing housing needs a large circular hole inthe mounting at the back.I suggest you use only one system of measurement, eithermetric or English and stick to that system. Your bestchoice of measurement system will depend on the magnetsize you choose.TolerancesMost of the dimensions given are nominal - the accuracy isnot critical, so you need to not follow the drawingsslavishly.The shapes of the blades are important near the tip butmuch less so near to the root (the larger, inner end of theblade).The alternator parts must be constructed and assembledwith enough accuracy that the magnets pass the coilscentrally as the machine rotates.DIAMETER
  3. 3. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 3Hugh@scoraigwind.co.ukCONTENTSIntroduction................................................................2Blades................................................................................ 2Alternator.......................................................................... 2Blades................................................................................ 2Furling system .................................................................. 2Units.................................................................................. 2Tolerances......................................................................... 2Glossary........................................................................4Workshop tools...........................................................5Materials for the large machine.............................6Notes on workshop safety........................................8GENERAL......................................................................... 8SPECIFIC HAZARDS ....................................................... 8METALWORK .................................................................. 8WOODWORKING ............................................................ 8RESINS AND GLUES....................................................... 8MAGNETS ........................................................................ 8ELECTRICAL.................................................................... 8BLADE THEORY..............................................................9Blade power ...................................................................... 9Blade speed....................................................................... 9Blade number ................................................................... 9Blade shape....................................................................... 9Carving the blades...................................................10STEP ONE is to create the tapered shape.......................10STEP TWO carving the twisted windward face..............10STEP THREE carving the thickness ............................... 11STEP FOUR Carve the curved shape on the back of theblade.................................................................................12STEP FIVE Assembling the rotor hub. ...........................12ALTERNATOR THEORY........................................15Preparing the bearing hub.....................................15Drilling out the 1/2 [12 mm] holes in the flange............16Fabricating the alternator mounts......................17Drilling the magnet rotor plates...........................19Making the coil winder............................................19Winding the coils......................................................20ELECTRICAL THEORY..........................................21Connecting the coils ................................................22Hints for soldering.......................................................... 22Soldering the coil tails .................................................... 22The ring neutral.............................................................. 22The output wiring........................................................... 23Making the stator mould .......................................23Mark out the shape of the stator.................................... 23Cut out the stator shape in plywood. ............................. 24Wiring exit holes............................................................. 24Screw the mould to its base............................................ 24Casting the stator....................................................25Dry run............................................................................ 25Putting it together........................................................... 25Removing the casting from the mould........................... 26The magnet-positioning jig ....................................26Making the two rotor moulds................................28Index hole ....................................................................... 28Parts of the moulds .........................................................28Casting the rotors ...................................................29Preparation......................................................................29Handling the magnets.....................................................29Dry run ............................................................................29Checking for magnet polarity .........................................29Putting it together ...........................................................29FURLING SYSTEM THEORY................................30Why furl?.........................................................................30How the furling tail works ..............................................30Controlling the thrust force ............................................ 31Fabricating the tail hinge......................................32The tail itself....................................................................33Cutting out the tail vane .......................................34Mounting the heatsink ...........................................34Assembling the alternator.....................................35Preparation......................................................................35Hub and shaft..................................................................35Back magnet rotor...........................................................35The stator.........................................................................35Front magnet rotor..........................................................36Testing the alternator ............................................36Short circuit tests ............................................................36AC voltage tests ...............................................................36DC voltage tests...............................................................36Connecting the rectifier.........................................37Connecting the battery ..........................................37Fuses or circuit breakers.................................................37Connections.....................................................................37Brake switch ....................................................................37Choosing suitable wire sizes..................................37Wire type .........................................................................38Fitting and balancing the blades .........................39Checking the tracking .....................................................39Balancing the rotor..........................................................39Fine tuning ......................................................................39ADDITIONAL INFORMATION......................................40Guyed tower ideas ...................................................40Controlling the battery charge rate....................41Shunt regulator circuit.................................................... 41List of components required........................................... 41Using polyester resin...............................................42Mould preparation ..........................................................42Small machine supplement....................................43Blades ..............................................................................43Bearing hub .....................................................................43The shaft..........................................................................44Rotor moulding ...............................................................44Stator mould....................................................................46Assembly of the stator.....................................................46The yaw bearing ..............................................................47The tail bearing and tail ..................................................47Wiring up the battery......................................................48
  4. 4. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 4Hugh@scoraigwind.co.ukGlossaryAC-Alternating current as produced by the alternator.Allthread - USA word for threaded or spun rod orstuddingBrake switch - A switch used to short-circuit the wiresfrom the alternator so that it stops.Catalyst - A chemical used to make the polyester resin setsolid. Catalyst reacts with accelerator already present inthe resin mix. The heat of reaction sets the polyester.Cavalier - A make of car. The cavalier in the UK is not thesame as the Cavalier in the USA but both have usefulwheel hubs.DC - direct current with a positive and a negative side, asin battery circuits.Diameter - The distance from one side of a circle toanother. The width of a disk right across the middle.Drag - A force exerted by the wind on an object. Drag isparallel to the wind direction at the object. (see Lift)Drop - Used here to describe a certain measurement of theshape of a windmill blade. The drop affects the angle ofthe blade to the wind.Flux - The stuff of magnetism. Similar to current inelectricity. It can be visualised as lines coming out of onepole and returning to the other.Furling - A protective action that reduces exposure toviolent winds by facing the blades away from them.Jig - A device used to hold the magnets in place beforesetting them in resin.Leading edge - The edge of a blade that would strike anobject placed in its path as the rotor spins.Lift - A force exerted by the wind on an object. Lift is atright angles to the wind direction at the object. (see Drag)Mould - A shaped container in which resin castings areformed. The mould can be discarded after the casting hasset.Multimeter - A versatile electrical test instrument, used tomeasure voltage, current and other parameters.Neodymium - The name given to a type of permanentmagnet containing neodymium, iron and boron. Thesemagnets are very strong and getting cheaper all the time.Offset - An eccentric position, off centre.Phase - The timing of the cyclical alternation of voltage ina circuit. Different phases will peak at different times.Polyester - A type of resin used in fibreglass work. Alsosuitable for making castings.Power - the rate of delivery of energyRectifier - A semiconductor device that turns AC into DCfor charging the battery.Root - The widest part of the blade near to the hub at thecentre of the rotor.Rotor - A rotating part. Magnet rotors are the steel diskscarrying the magnets past the stator. Rotor blades are thepropeller driven by the wind and driving the magnetrotors.Soldering - A method for making electrical connectionsbetween wires using a hot iron and coating everythingwith molten solder.Stator - An assembly of coils embedded in a slab of resinto form part of the alternator. The magnets induce avoltage in the coils and we can use this to charge a battery.Styrene monomer - A nasty smelling solvent in thepolyester resin mix.Talcum powder- A cheap filler powder used to thicken theresin and slow its reaction (prevent it overheating).Tail - A projecting vane mounted on a boom at the back ofthe windmill used to steer it into or out of the windautomatically.Tap - a tool for making thread inside holes so you can fit ascrew into the hole.Thrust - The force of the wind pushing the machinebackwards.Tower - The mast supporting the windmill.Trailing edge - The blade edge furthest from the leadingedge. The trailing edge is sharpened, so as to release thepassing air without turbulence.Wedges - Tapered pieces of wood used to build up theblade thickness and increase its angle to the wind near theroot.Workpiece - The piece of wood or metal being shaped inthe workshop.Yaw bearing - the swivel at the top of the tower on whichthe windmill is mounted. The yaw bearing allows thewindmill to face the wind.
  5. 5. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 5Hugh@scoraigwind.co.ukWorkshop toolsMECHANICALTOOLS• electric welder• saws-all• oxy-acetylene torch• welding mask• chipping hammer• vice• G clamps• pillar drill• cordless drill• handheld electric drill-- 1/2" [13mm] chuck• drill bits• holesaws• 1/2" [M12] tap• angle grinder• belt sander• cut-off machine• hacksaw• cold chisel• hammer• centre punch• files• tin snips• tape measure• steel ruler• set square• protractor• scriber• chalk• compasses• angle/bevel gauge• spirit level• vernier calipers• ear protectors• safety glasses/goggles• face masks• screwdrivers• pliers• vice grips• 10"adjustable wrench• combinationwrenches 3/8"-3/4"[10-19mm]• socket wrenches andratchets 10-19mmWOODWORKINGTOOLS• vice• G clamps• hammer• wooden mallet• draw knife• spoke shave• planes large andsmall• wood chisel• oilstone• jig saw• screwdrivers• handsaw• circular saw• pencil• tape measure• steel ruler• set square• spirit level• calipersPLASTICS ETCTOOLS• multimeter• surform/rasp• weighing scales• spoons, knives formixing• safety glasses• face masks• screwdrivers• knife• scissors• felt pen• soldering iron• pencils• tape measure• steel ruler• spirit level•MiscellaneousconsumablesWelding rods, grindingdisks, hacksaw blades.Epoxy glue and bondofor misc. repairs.Lead flashing forbalancing blades(1/8" x 12" x 12" approx.piece)Heatsink compound forrectifier mountingSome extra tools forthe smaller machine1" diameter woodboring bit for moulds.
  6. 6. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 6Hugh@scoraigwind.co.ukMaterials for the large machineBLADE WOODPieces Material Length Width Thick3bladesLight, straightgrained wood4 feet[1200mm]6 "[150 mm]1 1/2"[37mm]1wedgesOff-cut ofwood, withsome straight-grainedportionsEnough tofind someniceportionsOver 3"[75mm]1 1/2"[37mm]PLYWOOD ETC.Pieces Material Length Width Thick2lidsHardboard 16" [400] 16" [400] 1/8" [3 ]1jigHardboardor plywood12" [300] 12" [300] 1/4" [6]2islandPlywoodfor magnet6" [158] 6" [158] 1/2" larger[9] smaller1tailvaneExteriorplywood fortail vane36"[900 mm]24"[600]3/8"[9 mm]2hubdisksExteriorqualityplywood10"[250mm]10 "[250mm]1statorPlywood 24" [600] 24" [600]3coilwinderPlywood 4"[100 mm]3"[75mm]1/2"[13 mm]2lid andbaseSmoothfacedboard24" [600] 24" [600] 3/4" [19]suggestedsize4rotorsFloor board 16" [400] 16" [400] 3/4" [19]STEEL AND ALUMINIUMPieces Steel pipe Length OverallDiam.WallThick1Yawbearg.2" nominal 12"[300 mm]2 3/8"60.3 OD1/8"[3mm]1Yawbrg.1 1/2 "nominal bore16"[400 mm]1 7/8"[48 mm]1/8"[3mm]1 Tailboom1 1/4"nominal bore4 6"[1350 mm]1 5/8"[42.2]1/8"[3mm1 tailhinge1 " nominalbore8"[200 mm]1 5/16"[33.4]1/8"[3mmPieces Steel disk Diam. Thick Hole2 Magnet rotordisks12 " O.D.[300 mm]5/16"8 mm2 1/2[65 ]1 tailbearing capSteel platedisk orsquare1 5/8"[42.2]minimum5/16"[8mm]1 yawbearing capSteel platedisk orsquare2 1/2"[65]5/16"[8mm]Pieces Material Length Width Thic1tailhingeSteel plate 4"[100]2 1/4"[56 mm]3/8"[10]1tailSteel bar 12" [300]approx.1 1/2"[30] 5/16[8]2 Steel angle 10 1/2"[267 mm]2"[50 mm]1/4"[6 ]2 Steel angle 2"[50mm]2"[50 mm]1/4"[6 ]1 Steel angle 4"[100 mm]2"[50 mm]1/4"[6 ]1 Aluminiumangle orchannel9"[220 mm]2"[50]3/16"[5mm]MAGNETS24 Magnet blocks 2 x 1 x 1/2" grade 35 NdFeBItem 76 from www.wondermagnet.com[46 x 30 x 10 mm grade 40 NdFeB see belowUK SOURCES OF PARTSFibreglass resinetcGlasplies 2, Crowland St. Southport,Lancashire PR9 7RL(01704) 540 626Magnets CERMAG Ltd. 94 Holywell Rd, SheffieldSA4 8AS (0114) 244 6136or <sales@magna-tokyo.com>Winding wire EC WIRE LTD (01924) 266 377Percy Hawkins(01536) 523 22FARNELL www.farnell.comJPR Electronics www.jprelec.co.ukRectifiers andothercomponents www.Maplin.co.uk
  7. 7. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 7Hugh@scoraigwind.co.ukSTEEL FASTENERSPieces Material Length Width1mountsStainless steelall-thread rod5[1.5 m]1/2"[M12]40 Stainless steelnuts1/2"[M12]10 Stainless steelwashers1/2"[M12]4for rotormouldsBolts,nuts +washers3"[70 mm]1/2"[12 mm]4coil formerNails or pins 4" ?[100 mm ?]3/16"[5 mm]1winderStud or bolt(winder shaft)6" approx.[150 mm]3/8"[10 mm]5winderNuts andwashers3/8"[10 mm]3tail vaneBolts, nutswashers2 1/2"[60 mm]3/8"[M10]2heatsinkBolts and nuts 1" [25] 1/4" [6]6rectifiersBolts and nuts 1" [25] 3/16" [5]100 Wood screws 1 1/4" [32 mm]FIBERGLASS RESINQuantity Material6lbs[2.5 kg]Polyester casting resin or fiberglass resin inliquid form (premixed with accelerator).Peroxide catalyst to suit.5 lbs.[2.2 kg]Talcum powder3 x 3[1 x 1 m]Fiberglass cloth (or use chopped strand mat)1 ounce per sq. foot= [300g per sq. metre]Wax polishSilicone sealantWIRE ETCWeight Material Turns per coil& sizeVoltag80 turns of #15 wire[90 turns of 1.4 mm]12 V160 turns of #18 wire[180 turns of 1 mm]24V6 lbs.[3 kg]for tencoilsEnamelwindingwire, calledmagnet wirewww.otherpower.com320 turns of #21 wire[360 turns 0.7 mm]48V#14 [2 mm] or similar 12-V,30[10 m]Flexible wirewith hightemperatureinsulation#18 [.75 MM] bundledin a protective sleeve24V or48V3 [1 m] Resin coredsolder wire3 [1 m] InsulationsleevingLarge enough to fitover the solder joints5 Bridgerectifiers35A 6-800V single phasehttp://www.rfparts.com/bridge.htm1 ConnectorblockBEARING HUB1 Automotive rear hub with flanged shaft forconvenient mount to wind turbine.UKVERSIONHUBSHAFTHUB3"5.5"
  8. 8. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 8Hugh@scoraigwind.co.ukNotes on workshop safetyGENERALWorkshop safety depends on correct behaviour. Thereare intrinsic dangers. Be aware of the risks to yourselfand others and plan your work to avoid hazards.Protective clothing will reduce the risks, but withoutawareness the workshop will not be safe.Keep the workshop tidy. Avoid trailing leads, precariousbuckets or other unnecessary hazards, which peoplecould trip over or spill.Watch out for others, to avoid putting them at risk andbeware of what they might do which could put you atrisk.Wear protective clothing - eye protection, gloves, helmet,mask, etc as appropriate to prevent danger. Avoid looseclothing or hair, which could be trapped in rotating toolsand pulled inwards.Take care when handling tools which could cut or injureyourself or others. Consider the consequences of the toolslipping or the workpiece coming loose. Attend to yourwork, even when chatting to others.SPECIFIC HAZARDSMETALWORKGrinding, sanding, drilling etc can produce high velocitydust and debris. Always wear a mask when grinding.Take care that any sparks and grit are directed into a safezone where they will not injure anyone, or cause fires.Consider how the tool might come into contact withfingers or other vulnerable body parts.Welding, drilling etc makes metal hot, so take care whenhandling metalwork during fabrication.Welding should take place in a screened space where thesparks will not blind others. Wear all protective clothingincluding mask. Do not inhale the fumes. Protect theeyes when chipping off slag. Do not touch live electrodesor bare cable.Steel mechanisms can fall or fold in such a way as tobreak toes or fingers. Think ahead when handling steelfabrications to prevent injury. Clamp the workpiecesecurely.Take great care when lifting steel assemblies, to avoidback injury. Keep well clear of towers and poles thatcould fall on your head. Wear a safety helmet whenworking under wind turbines.WOODWORKINGTake care with sharp tools. Clamp the workpiecesecurely and consider what would happen if the toolslips. Watch out for others.Wear a dust mask when sanding. Do not force others tobreathe your dust. Take the job outside if possible.Wood splinters can penetrate your skin. Take care whenhandling wood to avoid cutting yourself.RESINS AND GLUESThe solvents in resins can be toxic. Wear a mask andmake sure there is adequate ventilation.Avoid skin contact with resins. Use disposable gloves.Plan your work to avoid spillage or handling of plasticresins and glues. Be especially careful of splashing resinin the eyes.MAGNETSMagnets will erase magnetic media such as credit cards,sim cards, camera memory cards, and damage watches.Remove suchlike from pockets before handling magnets.Magnets fly together with remarkable force. Beware oftrapping your fingers. This is the most likely cause ofsmall injuries. Slide magnets together sideways withextreme caution.ELECTRICALCheck for dangerous voltages before handling anywiring.Battery voltage systems are mostly free from dangerousvoltages, but there is a shock hazard from wind turbinesrunning disconnected from the battery. Under theseconditions the output voltage can rise to dangerouslevels.Even at low voltages there is a danger of burns fromelectric arcs or short circuits. All circuits from batteriesshould have fuses or circuit breakers to preventsustained short circuits causing fires.Be especially careful with batteries. Metal objectscontacting battery terminals can cause large sparks andburns. Gas inside the battery can be ignited, causing anexplosion that spatters acid in the eyes. Acid will burnclothing and skin. Avoid contact, and flush any affectedparts with ample water. Take care when lifting andmoving batteries to prevent back injury or acid spills.
  9. 9. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 9Hugh@scoraigwind.co.ukBLADE THEORYBlade powerThe rotor blade assembly is the engine powering thewind generator. The blades produce mechanical powerto drive the alternator. The alternator will convert thisinto electrical power. Both types of power can bemeasured in watts.Its a good idea to use metric units for aerodynamiccalculations. The power (watts) in the wind blowingthrough the rotor is given by this formula:1/2 x air-density x swept-area x windspeed3(where air density is about 1.2 kg/m3)The blades can only convert at best half of the windÕstotal power into mechanical power. In practice onlyabout 25 -35% is a more typical figure for homebuiltrotor blades. Here is a simpler rule of thumb:Blade power = 0.15 x Diameter2 x windspeed3= 0.15 x (2.4 metres)2 x (10 metres/second)3= 0.15 x 6 x 1000 = 900 watts approx.(2.4m diameter rotor at 10 metres/sec or 22 mph)Diameter is very important. If you doublethe diameter, you will get four times asmuch power. This is because the windturbine is able to capture more wind.Windspeed is even more important. Ifyou can get double the windspeed, you willget eight times as much power.Blade speedThe speed at which the blades rotate will depend on howthey are loaded. If the alternator has high torque and ishard to turn, then this may hold the speed down too low.If the wiring is disconnected and electricity production isdisabled, the rotor will accelerate and Ôrun awayÕ at amuch higher speed.Rotor blades are designed with speed in mind, relative tothe wind. This relationship is known as Ôtip speed ratioÕ(tsr). Tip speed ratio is the speed the blade tips traveldivided by the windspeed at that time.In some cases the tips of the blades move faster than thewind by a ratio of as much as 10 times. But this takesthem to over 200 mph, resulting in noisy operation andrapid erosion of the blades edges. I recommend a lowertip speed ratio, around 7.We are building a rotor with diameter 8 feet [2.4metres]. We want to know what rpm it will run at best ina 7 mph [3 m/s] wind when first starting to produceuseful power.Rpm = windspeed x tsr x 60/circumference=3 x 7 x 60 /(2.4 x 3.14)= 167 rpmBlade numberPeople often ask ÒWhy not add more blades and getmore power?Ó It is true that more blades will producemore torque (turning force), but that does not equate tomore power. Mechanical power is speed multiplied bytorque. For electricity production you need speed morethan you need torque. Extra blades help the machine tostart to turn slowly, but as the speed increases the extradrag of all those blades will limit how much power it canproduce. Multibladed rotors work best at low tip speedratios.Fast turning blades generate much more lift per squareinch of blade surface than slow ones do. A few, slenderblades spinning fast will do the same job as many wideones spinning slowly.Blade shapeAny rotor designed to run at tip speed ratio 7 would needto have a similar shape, regardless of size. Thedimensions are simply scaled up or down to suit thechosen diameter.We specify the shape at a series of stations along thelength of the blade. At each station the blade has ÔchordwidthÕ, blade angle and thickness. When carving ablade from a piece of wood (a ÔworkpieceÕ) we caninstead specify the width of the workpiece and also whatI call the ÔdropÕ. These measurements will then producethe correct chord width and blade angle. The drop is ameasurement from the face of the workpiece to thetrailing edge of the blade.The shape of the blade near the root may vary fromone wind turbine to another. A strongly twisted andtapered shape is ideal. But in some cases a much lesspronounced twist is also successful. I prefer the strongtwist and taper becausea) it is strongb) it is starts up better from rest,and c) I think it looks better.In fact it is not going to make a huge difference if theroot is a different shape. The blade root shape willprobably be determined more by practical issues such asavailable wood and the details of how to mount it to thealternator than by aerodynamic theory.WIDTHLEADINGEDGEOUTLINE OF WOODEN WORKPIECETRAILINGEDGEBLADEANGLEDROPCHORD WIDTHTHICKNESSBLADE STATIONSBLADE SECTIONDIAMETER
  10. 10. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 10Hugh@scoraigwind.co.ukCarving the bladesMaterialsPieces Material Length Width Thick3 Light,straightgrained wood4 feet[1200mm]6 "[150 mm]1 1/2"[37mm]The wood should be well seasoned and free of sap. It issometimes possible to cut several ÔblanksÕ out of a largebeam, avoiding knots. You can glue a piece onto the sideof the workpiece to make up the extra width at the root.Do not increase the length by gluing, as this will weakenthe blade.Check for any twist on the face of the workpiece, using aspirit level across the face at intervals along its length. Ifthe wood is levelled at one point, it should then be levelat all points. If the piece is twisted then it may benecessary to use different techniques to mark outaccurately the trailing edge (see next page).STEP ONE is to create the tapered shape.The blade is narrow at the tip and fans out into a widerchord near the root. This table shows the width youshould aim for at each station. You may wish to do themarking out once with a template of thin board. Thencut out and use the template to mark the actual blades.station width1 6 " 150 mm2 4 3/4" 120 mm3 3 15/16" 100 mm4 3 1/8" 80 mm5 2 3/4" 70 mm6 2 3/8" 60 mm• Mark out the stations by measurement from the rootof the workpiece.• Draw a line around the workpiece at each station,using a square (lines shown dotted).• Mark the correct width at each station, measuringfrom the leading edge, and join the marks up with aseries of pencil lines.• Cut along these lines with a bandsaw.Alternatively you can carve away the unwanted woodwith a drawknife. Or crosscut it at intervals and chop itout with a chisel. In any case the final cut face should bemade neat and square to the rest of the piece. Make eachblade the same.STEP TWO carving the twisted windward faceThe windward face of the blade will be angled, butsomewhat flat, like the underside of an aircraft wing.The angle will be steeper (removing more wood) at theroot than it is at the tip. The reason why blade-angleshould change is because the blade-speed becomesslower as we approach the centre. This affects the angleof the apparent air velocity striking the blade at eachstation.• Start by marking the stations (with a square) on theface you cut in Step One.• Then mark the drop on each of these new lines,measuring from the face of the wood as shown belowand marking the position of the trailing edge at eachstation.station drop1 1 1/2" 37 mm2 1 25 mm3 7/16 12 mm4 1/4 6 mm5 1/8 3 mm6 1/16 2 mm• Join these marks to form the line of the trailing edge.The leading edge is the other corner of theworkpiece.The ÔdropÕ near the root is not large enough to give thebest blade angle. In step six you will use a woodenwedge to build up the leading edge, and double theeffective drop. This wedge creates the desired blade-angle without needing such a thick workpiece. Leave aPENCIL LINES AT STATIONSMARK OUT THE SHAPE ON THE FACE OF THE WORKPIECE30LEADINGEDGECUT ALONG THIS LINE(CUT THE 30DEGREEANGLELATER)LEADINGEDGEDIRECTIONOFMOTIONTRAILINGEDGECENTREOFROTORTIPWEDGEwedgeA SERIES OF SECTIONAL VIEWS OF THE BLADE, TO INDICATE HOW THEYCHANGE IN SIZE AND ANGLE BETWEEN THE TIP AND THE ROOT OF THE BLADEROOT
  11. 11. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 11Hugh@scoraigwind.co.ukportion of the face uncut where the wedge will fit. In thisarea around the first station, you will be cutting a facebetween the trailing edge and the outline of the wedgefootprint.• Remove allthe woodabove thetrailing edgeline, so thatyou can placea straight edgebetween theleading and trailing edges.In this way you will be forming the twisted windwardface of the blade. I use a drawknife and a spoke-shave todo the inner part, and a plane is useful on the straighterpart. You can use a sander if you prefer. Take care to beprecise in the outer part near the tip where the bladeangle is critical. Do not remove any of the leadingedge, but work right up to it, so that the angled facestarts right from this corner of the wood.Leave the blade root untouched, so that it can be fittedinto the hub assembly. The hub will be constructed byclamping the blades between two plywood disks (see stepfive). The carving of the windward face ends with aramp at the inboard end. This ramp is guided by lines,which meet at a point just outside the hub area. The lineon the larger face has two legs Ð one for the wedge andone for the ramp.Checking the dropIf in doubt about the accuracy of the blade angle, use aspirit level to check the drop.• First use the level to set the blade root vertical (orhorizontal if you prefer, but be consistent).• At each station, place the level against the leadingedge and check the drop between the level and thetrailing edge.When measuring the drop, make sure that the level isvertical (or horizontal if appropriate). If the drop is toolarge or small, adjust it by shaving wood from theleading or trailing edge as required.STEP THREE carving the thicknessThis table shows the thickness of the blade section.station thickness1 1 3/8 36 mm2 15/16 25 mm3 1/2 13 mm4 3/8 10 mm5 5/16 8 mm6 1/4 7 mm• At each station, measure the appropriate thicknessfrom the windward face, and make a mark. Join themarks to form a line.• Do this again at the trailing edge.• Where the thickness runs out at the trailing edge,draw a diagonal line across the back of the workpieceto meet the line at the leading edge.TIPPOSITION ASET THE BLADEVERTICALONEDGETIPPOSITION BSET THE LEVEL AGAINSTTHE LEADING EDGE,AND MEASURE THE DROPRULERTHICKNESSREMOVETHIS PARTUP TO THELINETRAILINGEDGELEADINGEDGETRAILINGEDGETIPTRAILINGEDGEREMOVETHISPARTGUIDELINEGUIDELINELEADINGEDGETIPSTATION MARKSREMOVEEVERYTHINGABOVETHIS TRAILING EDGE LINEKEEP THIS PARTUNTOUCHEDDROPLEADINGEDGEMIDLINE8"[200]6"[150]3"[75]5"[125]
  12. 12. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 12Hugh@scoraigwind.co.ukThese lines will guide you as you carve the section, toachieve the correct thickness. Carve the back of theblade down to these lines.• As you approach the lines themselves, you shouldbegin to check the thickness with callipers at eachstation.Both sides of the blade should now be flat and parallel toeach other, except at the inner part where this is notpossible, because the workpiece is not thick enough toallow full thickness across the whole width. In this areayou need not worry about the part nearer to the tailingedge, but try to make the faces parallel where you can.The final blade section will only be full thickness along aline that runs about 30% of the distance from leading totrailing edges.STEP FOUR Carve the curved shape on the backof the bladeThe blade is nearly finished now. The importantdimensions, width, angle and thickness are all set. Itonly remains to give create a suitable airfoil section ateach station. If this is not done, the blade will have veryhigh drag. This would prevent it from working well athigh tip-speed-ratio.The first part of this step is to make a feathered trailingedge. Take great care to cut only into the back of theblade. This is the face you just cut out in step three. Donot touch the front face. (You carved the front face inStep Two.)• Draw two lines along the back of the blade, at both30% and 50% width measured from the leadingtoward the trailing edge. The 50% line is to guideyou in carving the feathered trailing edge.• Now carve off the part shown hatched, between thetrailing edge and the middle of the blade width. Thiswill form the correct angle at the trailing edge. Whenyou have finished, it should be possible to place astraight edge between this line and the trailing edge.The trailing edge should be less than 1 mm thick.• When this is done, the blade has to be carved into asmoothly curving shape according to the sectionshown.It is hard to prescribe exactly how to produce the curve.The best description is simply Ôremove any cornersÕ. Asyou remove corners, you will produce new corners,which in turn need to be removed. Run your fingers overthe wood lightly to feel for corners. Remove less woodeach time.Take care not to remove too much wood. The 30% linerepresents maximum thickness part and should not becarved down further. Take care not to produce a cornerat this thickest point.STEP FIVE Assembling the rotor hub.MaterialsPieces Material Diameter Thick2disksExterior qualityplywood10 inches[250mm]1/2"[13 mm]54 Woodscrews 1 1/4" [32 mm]Cutting the roots to 120 degreesIf the roots of the blades have not already been cut to a120 angle already, then this is the time to cut them.THICKNESS30%70%CHECK FOR THICKNESSAT 30% CHORD WIDTHFROM THE LEADINGEDGELEADINGEDGEMAXIMUMTHICKNESSHERETHICKNESS30%50%REMOVETRAILINGEDGEMAXIMUMTHICKNESSHERECUT BEVELTOHEREFINISHEDBLADE
  13. 13. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 13Hugh@scoraigwind.co.uk1 3/4"[44mm]90°60120MIDLINE• Draw a mid-lineat 3" [75 mm]from each edge.• Draw a line atright angles(90degrees) tothe edge, and 13/4 [44 mm]away from theblade root. Theblade root maynot be square.Be sure that this line is drawn square.• Draw angled lines connecting the ends of this line tothe point where the mid-line hits the end as shown.These two lines should turn out to be angled at 120degrees to the edge of the wood.• Saw off the triangular pieces from the corners bycutting along the angled lines, leaving a central 120-degree point on the blade root. Set the lines upvertically while you cut the workpiece.Marking and drilling the plywood disksChoose one disk to be the master. Draw a circle at thesame diameter as the mountinghole centres.Lay the front (outer) magnetrotor onto the disk centrallyand drill five 1/2" [four 12 mm]holes through the disk.Carefully mark the disk withany index marks so that you canplace it against the magnetrotor in exactly the sameposition again.Draw two circles on the diskusing diameters 6"[150] and8"[200].Use the compasses to walkaround the outer circle markingsix, equally spaced points.Use every second point to drawa line radiating from the centre.Each line represents the middleof one blade for the purpose ofmarking out screw holes(nothing accurate more thanthat).Now set the compasses for a 1"[25 mm] radius and walk themaround the outer circle for two steps from the line ineach direction, marking five hole centres.Mark another four hole centres with the compasses onthe inner circle in a similar fashion but straddling thecentre line.Place the master disk on top ofthe other plywood one centrallyand lay them on some wastewood for support. Drill 27neatly spaced screw holesthrough both disks.Countersink the screw holesfrom the outsides. Considerwhich face will meet the magnetrotor.Clamping the blades togetherLay the blades out on the floor, windward face down(curved faces up). Fit the root together. Make equalspacing between the tips.Make a mark on each blade at 5"[125mm] radius fromthe centre of the rotor.MASTER DISKMATES WITHFRONTMAGNETROTOR3 " [ 7 5 ]6"[150]SAW3"[75]1 1/2"[37mm]
  14. 14. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 14Hugh@scoraigwind.co.ukPosition the master disk centrally on the blade roots byaligning the disks edges on these marks. Screw it ontothe blades with 9 screws per blade.Turn the assembly over and repeat, using the other disk.Turn it back again. Mark the centres of the four 1/2" [12mm] holes by drilling very slightly through the masterdisk into the blades. Remove the master disk. Lay thefront of the hub on waste wood, and use a 5/8" [16mm]drill to follow through at the same positions. Take greatcare to drill square to the face.These holes provide a clearance fit for the 1/2" [M12]studs that secure the blade assembly to the alternator.The assembly locates precisely on the master disk.Now unscrew the front disk, ready for painting.STEP SIX Cutting out and gluing on the wedgesMaterialsPieces Material Length Width Thick1 Offcuts ofwood, withstraightgrainedportionsEnough tofind someniceportionsOver 3"[75mm]1 1/2"[37mm]This diagram shows the dimensions of the wedges. Thesimplest way to produce them is to cut them from thecorners of blocks of wood as shown.Choose a clear part of the block and draw two lines atright angle to the corner, shown dashed in the diagram.Measure out the 3" and the 1 1/2", and draw the angledlines, marking the cuts you will make. To cut out thewedges, place the block of wood in a vice with one linevertical. Align the blade of the saw carefully so that itlines up with both lines demarcating the cut. Then sawout the wedge.The position to glue the wedge on is shown in Step Two.Paint the blades and disks before final assembly.SANDWICH THEBLADEROOTSBETWEEN TWODISKSSPACE THE BLADETIPS AT EQUALDISTANCES APARTSCREW EACH DISKSTO THE BLADESWITH 9 SCREWSPER BLADE
  15. 15. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 15Hugh@scoraigwind.co.ukSTATORSTUDROTORYAWBEARINGALTERNATOR THEORYThe alternator consists of a stator disk sandwichedbetween two magnet rotors. Strong magnetic flux passedbetween the two rotors and through the coils in thestator. The movement of the rotors sweeps the fluxacross the coils, producing alternating voltages in them.This sectional viewshows the rotatingparts in black. Four1/2"[12 mm]allthread studs[threaded rod]support the twomagnet rotors onthe hub flange, andkeep them at thecorrect spacingapart from eachother. The samestuds are also usedfor mounting theblades on the frontof the alternator.There are 12 magnet blockson each rotor. We embedthe blocks in a polyesterresin casting to supportthem, and to protectthem from corrosion.Each magnet block has anorth pole and a south pole. Thepoles are arranged alternately, so north faces the statoron one block and south on the next. The poles on theother magnet rotor are arranged inthe opposite polarity, so that northpoles face south poles across thestator. In this way, a strongmagnetic flux is created through thestator between the magnet rotors.Magnetic flux travels best throughsteel. The rotor disks are made fromthick steel plate to carry the flux.But the magnets have to work hardto push flux across the gaps, becausethere is no steel. A wider gap allowsmore room for a fatter stator, butweakens the flux.The statorThe stator is mounted at three points around itsperiphery, using three more 1/2" [12 mm] studs. Thecoils embedded within it are dimensioned such as toencircle the flux from one magnet pole at a time. As themagnet blocks pass a coil, the flux through the coilalternates in direction. This induces an alternatingvoltage in each turn of the coil. The voltage isproportional to the rate of change of flux. Voltagetherefore depends on:• the speed of rotation• the density of the flux• the number of turns in the coil.The number of turns of wire in each coil is used tocontrol the speed of the wind turbine. If the number ofturns is large, then the output will reach battery voltageand start to charge the battery at a low rotational speed(rpm). If we use fewer turns of thicker wire in the coils,then it will need to run faster. The number is chosen tosuit the rotor blades and also the battery voltage.There are ten coils in the stator. The twelve magnetpoles pass the coils at different times. This phase lagbetween coils means that the torque is much smootherthan it would be if there were 12 coils. If all the coilswere synchronised with each other (single phase) thenthe machine would vibrate quite intensely whenproducing power.Preparing the bearing hubA wheel-bearing hub from a car makes a good bearingfor the alternator. In the UK, Vauxhall Cavalier rearbearing hubs from around B or C registered vehiclesare ideal for example. Remove the stub shaft from thevehicle by removing four screws in the rear flange. Keepthe screws if possible.THE STATORCASTING CONTAINSTEN COILS
  16. 16. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 16Hugh@scoraigwind.co.ukThe level of corrosion isusually pretty high butthis need not be a worry.Undo or drill out thesmall retaining screw onthe brakedrum. Removethe brake drum using ahammer and a lever.Prise off the dust coverfrom the bearings.Remove the split pin andundo the retaining nut.Dismantle the bearingsand inspect them. If theylook worn or corroded,replace them. Thisentails knocking out theouter shells from the hub casting and replacing them too.Bearing sets are available from motor parts factors. Youcan discard the seal at the back of the hub. It will createtoo much friction and is not necessary.Clean all parts with a rag or paint brush and somegasoline [petrol] or parafin. Take special care to cleanthe bearing races meticulously if you plan to re-usethem. When the time comes for re-assembly of the hubto the shaft, grease the old bearings lightly to preventexcessive friction. Tighten the retaining nut with aspanner, rotate the hub and slacken the nut again.Tighten with fingers and check that there is no slack butthe hub revolves freely. Lock the nut with a split pin andreplace the dust cover.In the USA it may be easier to find a different type ofwheel hub with five holes in the wheel. The Americanhubs made by General Motors for the Citation, Cavalierand other medium sized cars has a wheel flange with fivestuds.The USA/GM hub is like the UK hub reversed. The GMhubs wheel flange is mounted on a shaft that runs insidea bearing, rather than being mounted on a bearing thatruns on a shaft. Consequently the bearing is at the backend in this type of hub. The inboard end of this hub unitalso has a flange.Drilling out the 1/2 [12 mm] holes in the flangeThe wheel flange on the hub already has four holes in it.The holes may also have wheel studs in them. Knock anywheel studs out with a hammer. We need to enlarge theholes to 1/2" [12 mm] diameter. Support the hub on adrill press so that the flange is level, and drill the fourholes out with a 1/2" [12 mm] drill.The holes in the shaft rear flange may have been tappedout with an unusual thread. If you still have the originalscrews in usable condition, this is not a problem. If notthen enlarge these holes to 3/8" [10 mm]. Then you canuse 3/8" [M10] bolts and nuts.The rear flange may have a bulge or projection in thecentre. It may be possible to grind this off. If not thenyou will have to make a hole in the mounting bracket toaccommodate this lump.Look ahead two pages for a mounting diagram for theGM hub with bearing housing at the rear.BEARING HUBAND SHAFTREARVIEWSECTIONFRONTVIEWBEARINGS1/2" [12 mm]HOLES AT4"[100 mm] PCDWHEEL FLANGEUS TYPE WHEEL BEARINGWITH FIVE HOLESBEARINGREARFLANGE
  17. 17. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 17Hugh@scoraigwind.co.ukFabricating the alternatormountsMaterialsPieces Material Length Diameter Thick1 Steel pipe2" nominal12" [300] 2 3/8"60.3 OD1/8"3 mm1 Steel plate 2 1/2"[65] 2 1/2"[65] 5/16"2 Steelangle10 1/2"[267 mm]or 11 1/2" forGM hub2"[50 mm]1/4"[6 ]2 Steel angle 2"[50mm]2"[50 mm]1/4"[6 ]1 Steel angle 4"[100 mm]2"[50 mm]1/4"[6 ]The centrepiece of the wind turbine mounting is the yawbearing. A 12" [300 mm] piece of 2"nominal bore pipe(60.3 mm overall diameter) will be used for the outerpart of this bearing assembly. Weld a small disk onto thetop of this pipe. An off-cut from the magnet-plate hole-saw operation is perfect. First enlarge the central hole toabout 3/4" [20 mm] for wiring down the tower/mast.Take care to weld this top plate on square.The yaw bearing pipe will simply drop onto a piece of1.5" nominal bore steel pipe and rotate on it with somegrease (and maybe a washer) between them. Its such asimple concept that most people cant believe it but itworks very well. In small wind turbine design, thesimplest solutions are usually the most successful andreliable, as well as being cheap and easy.The alternator mounting bracket consists of two piecesof 2" x 2" x 1/4" [50 x 50 x 6 mm] steel angle, each10 1/2" [267 mm] long. They are welded to the centre ofthe yaw bearing outer tube, to form a channel into whichthe rear flange of the shaft fits, and is bolted on. Seenext page for analternative style to suit theGM type of hub found inthe USA.The ends of the pieces ofangle will need to beshaped with a grinder tothe curve of the yaw-bearing pipe beforewelding. Note that thecurve is symmetrical, andthe bracket therefore sitscentrally on the pipe inboth directions. In thecase of the GM hub thecurve is asymmetrical butyou can place the pipe overthe piece of angle in the correct position and drawaround it.The bracket face should be near vertical (parallel to theyaw bearing). If there is any tilt, it should be slightlyclockwise in the above side-view. This would increase theclearance of the blade tips from the tower.Position the shaft flange centrally between the upper andlower faces of the channel, and 5"[125 mm] away fromthe centre of the yaw bearing. It is not easy to measurethis offset as such but if you measure the shaft diameteras 15/16" [24 mm] (say) then you can compute that thespace between the outside of the yaw pipe and the side ofthe shaft must be 3 1/4" [83 mm]. (125 mm - (60 +24)/2) = 83 mmUse a suitable drill size (5/16" [9 mm]?) to mark thepositions of the four holes and then drill them out 3/8"[10 mm] to fit the mounting bolts.5"[125]3 1/4"[83 mm]10 1/2"[267] 12"[300]60WELDSALTERNATORMOUNTING BRACKET4"[100]2"[50]BEARING HUBPLAN VIEWSHAFTHUBSIDE VIEWSECTION
  18. 18. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 18Hugh@scoraigwind.co.ukMounting diagramsThere are two diagrams onthis page to show the twodifferent types of hub. Thetop diagram is for the UKCavalier hub. The lowerone shows the USAGeneral Motors hub.The bearing is at the backend in the USA type ofhub. The inboard end ofthis hub unit has a flangethat you can use to mountit within the channel, butthe bearing housingprojects beyond this rearflange. To mount this unitwithin the support bracket,you have to cut a holeabout 3" in diameterthrough the bracket.Secure the rear flange tothe bracket with four 1/2"bolts as shown in the lowerdiagram.The stator will be mounted onthree 1/2" studs. The studs intheir turn will be supported bythree lugs made from 2" [50mm] steel angle. The lengthsof angle required are 2"[50],2"[50] and 4"[100 mm]. The4" [100 mm] length needs tobe welded across the end ofthe shaft support bracket(channel section) describedabove. The smaller bracketswill be welded directly to theyaw bearing tube, top andbottom.Stator lug positionsThe USA magnet version hasslightly different statordimensions from the UKmetric magnet version. Theupper drawing applies to UKmagnets, and the lower one isfor 2" x 1" USA magnets.2 1/4"6 "1 "2 3/4"4 1/8"2 7/8"1 1/4" YAWBEARING2 "11 1/2"ANGLEBEARINGHUB1/2" STUDCENTRE7 5/8"5 "1 1/4"1/2"ANGLE4 "8 "1 1/4"2 1/2"2 1/2"FLANGETHE US VERSION WITH THE GM HUBSIDE VIEWTHERE ARE FIVE STUDSIN THE FLANGE OF THEGM HUB2 "1 1/4"6 1/2"REAR VIEWTOP VIEWTOP VIEWROTORSTATORROTOR1/2" [M12]STUDUKVERSION WITH VAUXHALL CAVALIER HUBASSEMBLED ALTERNATOR SHOWING STATOR MOUNTING LUGSSTATORMOUNTBEARING HUB1 1/4"[30]SIDE VIEW1 1/4"[30]3"[75]3"[75]TOP VIEW
  19. 19. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 19Hugh@scoraigwind.co.ukDrilling the magnet rotor platesThe magnet rotors consist of 12" [300 mm] diameterdisks, cut out of 5/16" [8 mm] mild steel plate. 12magnet blocks will be mounted on each magnet-plate,and encapsulated in a polyester resin casting.The steel plates are then mounted on the bearing hub insuch a way that the magnets face each other across asmall gap. The stator will be mounted in this gap.Once the hub flange has been drilled, it can be used as aguide for drilling the hole patterns in the magnet plates.This is more accurate than marking out all the centres ofthe magnet-plate holes by hand. It is important that theholes align accurately with the hub holes, or themounting studs will be squint (in USA = askew).Use a holesaw to cut aclearance hole for thebearing stub on the hub.A 2 1/2" [65 mm]holesaw is a good size.This will allow the rearmagnet-plate to sit flaton the hub flange. It isalso useful to have alarge hole in the secondmagnet-plate. Keep theoff-cut disks from theholesaw for use in theyaw bearing and tailbearing.Bolt the bearing hubonto each magnet-platein turn and revolve thebearing to check forcorrect centring. Prop aruler or piece of wireclose to the edge and adjust the position until the plateruns true. Tighten the clamps and drill holes throughthe flange holes and into the plate. Fit a bolt into eachhole as you go and re-check the centring. Make an indexmark to record the position of the disk on the hub forfuture reference during assembly. Drilling an index holethrough the hub flange and both disks is a good way tokeep track of the positions. Mark the faces of the disk forcorrect reassembly.Repeat this operation using the front plate. Finally drilltwo 3/8" [10 mm] holes in the front plate on the samecircle as the 12-mm holes, but midway between them.Tap these holes out with 1/2" thread [M12]. These holeswill be used to jack the font plate on and off thealternator using long 1/2" [M12] screws. This isnecessary because the forces pulling the magnet rotorstogether will be very large when the magnet blocks havebeen added to them.Remove any burr from the edges of all the holes. Themagnet-plates are now almost ready for resin casting.(See Casting the rotors). Sand them at the last minute.Making the coil winderMaterialsPieces Material Length Width Thick3 Plywood 4"[100 mm]Over 3"[75mm]1/2"[13 mm]4 Nails 4"[100 mm]3/16"[5 mm]1 Stud orbolt6" approx.[150 mm]3/8"[10 mm]5 Nuts andwashers3/8"[10 mm]Make a coil-winding machine from pieces of 1/2" [13mm] plywood mounted on a 3/8" [10 mm] bolt orallthread stud. Form the coil on four pins made fromfour-inch nails cut off short.2.5 6 8 1 2 12.5MAGNET BLOCK2" X 1" X 1/2"GRADE 35NdFeB4630MAGNET10 THICKCASTINGOD310STEELDISK OD300MAGNET ID208HUB HOLE65Ø12HOLECASTINGID 158RESINCASTINGSTEELPLATEGRADE 40 NdFeBFRONTAL VIEWS OF MAGNET ROTORS FOR THE TWO VERSIONSREAR STEEL PLATE1/2"[12 mm]HOLE12"[300 mm]DIAMETER5/16"[8 mm]THICK2 1/2"[65 mm]HOLEFRONT STEEL PLATE1/2"[M12]TAPPEDHOLES
  20. 20. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 20Hugh@scoraigwind.co.ukThe sides of the coilsare supported by twocheek-pieces, held 1/2"[13 mm] apart by acentral spacer.Each cheek piece hasdeep notches inopposite sides, to allowyou to slip a piece oftape around thefinished coil. The tapewill hold the coiltogether when youremove it from thewinding machine.Fit a handle to one ofthe cheek pieces. Youcan use a small boltcarrying a piece of pipefor comfortablehandling. The head ofthe bolt must be sunkinto the wall of thecheek piece to preventit from catching on thewires.The positions of theholes for the nails willdepend on the magnetshape. The top drawingis for the USA versionwith 2" x 1" magnetblocks. Note that thespacer has to betrimmed at the ends toclear the nails. Takecare to drill the holessquarely into thecheeks.Its a good idea tochamfer the corners ofthe cheek pieces slightly on the inside. This prevents thewire from catching on the corners as the windingmachine revolves.The 3/8 [M10] bolt is used as an axle. It rides in a holethrough a piece of wood. It may turn more freely if thehole is lined with a bush of some sort - maybe a metalpipe. Tighten the nuts on the cheek pieces but not on thesupporting bearing.Winding the coilsChoose your wire to suit the magnet size and batteryvoltage. Metric sizes are suitable for metric magnetblocks.MaterialsWeight Material Turns per coil & size Voltage80 turns of #15 wire[90 turns of 1.4 mm]12 V160 turns of #18 wire[180 turns of 1 mm]24V6 lbs.[3 kg]for tencoilsEnamelwindingwire, calledmagnet wire320 turns of #21 wire[360 turns 0.7 mm]48VBuild a stand for the reelof copper winding wire.Take care to keep thewire straight. Avoidbending it unnecessarilyor scraping in theenamel. Align the coilwinder to the reel stand,so that the wire can feedinto it parallel to thecheek pieces.Make a tight 90-degree bend about 4" [100 mm] fromthe end of the wire and place it into the coil winder, in anotch in the outer cheek piece. Tuck the wire in closeagainst the cheek piece. Wind the tail of wire around the3/8"[M10] nut, such that it cannot slip off.Now grasp theincoming wire withone hand. Wind thehandle with theother hand,counting the turnsas you go. Use thefirst hand to keep agentle tension in the wire, and to control how it lies inthe winder. Lay the turns of wire together snugly, andbuild the coil turns up in neat layers. Work from oneside gradually across to the other and gradually back. Donot allow the wire to wander to and fro from side to sideor the coil will not be able to accommodate the necessarynumber of turns.When you have theright number ofturns of wire on thewinder, it is time totape the coil. Do notrelease the tensionin the wire until it issecurely taped.Slide the end of apiece of tape underthe coil using theWIREREELHOLDER2 x 1 2.53.5COIL LEG IS3/4 WIDE1.5"1.5"1 "3/8 [10]HOLE1/2 [13] THICKPLYWOODCHEEK PIECE (TWO OFF)FOUR HOLES 3/16" [5]3" [75mm]4"[100 mm][37.5][25][37.5]3/8"[M10]HSHAPEDCHEEKPIECESWINDINGHANDLEPIPEEMBEDDEDIN WOODIS USED ASBEARINGBUSHSTEEL PINS(SAWN OFF4" NAILS)8"[208]SPACER2" X 3/4"13/16"1+13/16"HOLE LOCATIONS1/2" THICKSPACER46 x 20 mm25mm41 mmHOLE LOCATIONS13 mm THICKUK VERSIONUSA VERSION
  21. 21. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 21Hugh@scoraigwind.co.uknotch and wrap it securely. Do the same on both sidesbefore you release the tension.Check that the dimensions of the coil are as shown.Repeat this process until you have ten coils.If in doubt about the number of turns, weigh each coiland compare them. Small errors are not significant butthe weights should be the same within 5% or so at worst.The ten coils will be laid out in a circle to match themagnet blocks. The spacing between the inner edges ofthe holes will be 8 inches, or 208 mm for the metricmagnets, as shown.ELECTRICAL THEORYThe electrical output of the wind turbine can bemeasured as a voltage and a current. Voltage iselectrical pressure and is usually constant for aparticular supply (hence 12-volt or 240-volt supply).You can measure the voltage of a supply with a multi-meter. Touch the two probes of the meter to the twowires from the supply and read out the voltage.Current in electric circuits can also be measured.Current in amps normally varies slowly from zero tosome high value and back, as time goes by andconditions change. When current flows in electricalcircuits, then power is being transmitted from thesupply to the load.This diagramshows two sortsof ammeter.One isanalogue, andthe other is adigital clamp-meter. In bothcases thecurrent passesthrough themeter in someway.Here the supply is a battery and the load is a bulb. Thesupply can be a wind turbine and the load can be abattery. In either case the power transmitted ismeasured in watts. Power output is calculated bymultiplying the voltage by the current. For example a20-amp current in a 12-volt circuit delivers 240 watts.There are two types of supply, AC and DC. Batteriesalways provide Direct Current (DC). DC is constant in itspolarity and magnitude over time. One wire is termedpositive and the other negative.The mains grid on the other hand supplies AlternatingCurrent (AC). In the case of an AC supply, the polarityreverses constantly, many times each second, and themagnitude rises and falls in a waveform. AC can beconverted to DC using a rectifier, consisting of a numberof one-way junctions called diodes.You can use a multimeter to measure AC voltage, but youneed to change the selector switch to ACV. The voltagedisplayed will be a sort of average value of theconstantly varying level.The alternator in our wind turbine produces 5-phase AC.This means that the voltages from the coils are rising andfalling at different times from each other. Here is agraph, showing how the voltages vary over time.We connect the coils in starconfiguration, with all the startstogether and the AC output takenfrom the finish tails. Connectingthese tails to a rectifier convertsthe AC into DC by only allowingthe current to flow in one directionthrough the DC output circuit.The voltage produced by the coilswill depend on both the speed ofrotation (see Alternator Theory)and also on the current supplied bythe alternator. Some voltage is lostinternally when there is currentthrough the coils.DCV10MULTIMETERBULB 12.36batteryBULBbatteryA2.055-phase AC voltagetime axisSTART FINISHSTART FINISHCOIL CONNECTIONSRECTIFIERCOILCOILEACH DIODE ALLOWS CURRENT TO FLOWONLY IN THE DIRECTION OF THE ARROWSTART FINISHSTART FINISHCOILCOILSTART FINISHSTART FINISHCOILCOILSTART FINISHSTART FINISHCOILCOILSTART FINISHSTART FINISHCOILCOIL+-OUTPUT
  22. 22. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 22Hugh@scoraigwind.co.ukConnecting the coilsMaterialslength Material Size Voltage#14 [2 mm]or similar12-V30[10 m]Flexible wirewith hightemperatureinsulation#18 [0.5 mm]or similar24-V or48-v3 [1 m] Resin coredsolder wire3 [1 m] InsulationsleevingLarge enough to fitover the jointsHints for solderingUse a clean soldering iron and makes sure it is hot beforeyou start. Touch some solder wire onto the tip of theiron and it should melt on instantly.Twist the wires together in a joint and place the tip of theiron against this joint so as to achieve maximum contactarea. Wait a second or two and then feed solder wireinto the point of contact between iron and joint. Thesolder should melt into the joint and assist with carryingheat further into the joint. Give it time. Keep the ironthere until the joint is full of solder and then remove.Take care not to disturb the joint until the solder sets (2seconds). Never try to add solder to a joint from theiron. The solder must come from the reel of solder wire.The resin core in the wire helps the solder to flow intothe joint.Soldering the coil tailsThe copper winding-wire has enamel coating whichinsulates it from its neighbours inthe coil. Before soldering the endsonto flexible tails, you must cleanthis enamel off a short length.Scrape 3/4" [20mm] of the coatingoff the end of the wire with a sharpknife or sandpaper. Use thesoldering iron and some solder tocoat or tin the end of the wire withsolder. Twist the flex around thetinned wire or place them side-by-side, bind them with a thin strandof copper. Then solder themtogether. Slip some insulationsleeving over the joint.Lay the coils in the stator mould asshown below. They all have to beexactly the same in orientation,with the starting tail on top. Itdoes not matter if your coils are amirror image of the ones shown so long as they are allthe same.The ring neutralTake a piece of flexible stranded insulated wire (flex),and make a loop that fits snugly around the outside ofthe coils in a ring. The loop will rest against the outeredges of the coils in such a way as to hold them in,against each other in the desired position.(See "winding the coils" for correct spacing of 8" [208mm]). There should be about 3/16" [5 mm] between theinside of the coils and the central disk.Before soldering theinsulated flex finallyinto a loop, cut tenlengths of sleeving 11/2" [30 mm] long, andthread them all ontothe loop. Strip about1/2" [15 mm] ofinsulation off the flex atequal intervals, to allowsoldered connections ateach coil as shown.Then solder the ends ofthe flex together so theloop fits around the tencoils with no slack.This loop of flexiblewire is the ring neutralconnecting all the startstogether. It will haveno direct connection toanything else.RINGNEUTRALSOLDEREDCONNECTIONEXITHOLEEXITHOLE
  23. 23. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 23Hugh@scoraigwind.co.ukThe output wiringThe finishes of the coils provide the output to therectifier. Each finish wire needs a tail of flex soldered toit. The tails are then brought out through the two holesin the mould. The second diagram shows the outputtails without showing the ring neutral. It also shows thepositions where the mounting holes will be drilled.Take care to make the tails long enough to reach therectifier. Use cable ties to secure the flex wiring togetherneatly. Ensure that they are secured away from thepositions of the mounting holes or they could bedamaged during the drilling of these holes.When the wiring is complete, carefully slide the coilassembly from the stator mould and place it on a flatsheet of board. You can slide it into place in the castingwhen the time comes.Making the stator mouldMaterialsPieces Material Length Width Thick1 Plywood 24" [600] 24" [600] 1/2" [132 Smooth facedboard24"[600]24"[600]3/4" [19]suggested siSilicone sealantWax polish3 1/4" [6mm] x 1 1/2" [35mm] Bolts10 ScrewsThe ten coils should fit neatly into a flat mould, wherethey will be encapsulated in polyester resin to form thestator. The stator will have a hole in the middle throughwhich the four rotor-supporting studs will pass. At theperiphery it will have three lugs where it is to besupported by 1/2"[M12] stainlessallthread studs.Mark out the shape of the stator.Use the metric figures for themetric magnets• Start with a piece of 1/2"[13 mm]plywood approximately 24"[600]square.• Draw vertical and horizontalcentre-lines, at exactly 90 degrees, and anoffset vertical line 5" [125 mm] tothe right of the vertical line.• Draw two circles on the intersectionof the centre lines. The radius for theinner circle is 3"[79 mm] and theouter circle is 7+3/8"[190].If you have no compasses big enough,then a strip of plywood will often workbest. Drill a hole for a pencil at one point,and screw a wood-screw through atanother point spaced at the correctradius.• Mark the mounting-hole centres7+5/8" [196] away from the centre.Mark two centres on the offset line. Theseparation should be 11+1/2"[300 mm]. Mark thethird holes centre on the horizontal centre-line,opposite the offset line. Do not drill any holes yet!• Draw arcs on these three hole-centres at1+1/4" [30 mm] radius. These describe the7+3/8511.57+5/8CENTRELINE24" SQUARE PIECE OF 1/2" PLYWOODCENTRELINESTATOR MOULD6"DIAMETERHOLE7+5/8EXITEXIT[125][190][196][190][300][158][600] [13mm]
  24. 24. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 24Hugh@scoraigwind.co.ukoutsides of the mounting lugs. Finally use a ruler toconnect the big circle to these new arcs withtangential lines so that the outside edge of the statoris a smooth shape. Do not cut the mould outyet.Sandwiching the stator mould.While being cast, the stator will be sandwiched betweentwo smooth-faced boards: a base and a lid. Discardedkitchen cabinets or worktops are good for this purpose,or you can use thick composite board for strength, andadd smooth hardboard for the finish.• Stack the three boards on top of each other. Thesmooth faces of the lid and the base need to be incontact with the mould plywood.• Drill three locating holes through the stack so thatyou will be able to reassemble the sandwichaccurately. This will help you get things in the rightplaces. Fit each hole with a suitable bolt (say 1/4"[6mm]).• Mark the boards for correct reassembly - lid, mould,base - tops and bottoms labelled clearly.• Fit the mould to theunderside of the lid, anddrill through the surroundinto the lid with plentiful3/16" [5 mm] holes for lateruse by clamping screws.Space these holes about 1"[25 mm] away from the lines.You will later be able to screw thelid down hard to the base and squeeze the castingthickness to a minimum.Cut out the stator shape in plywood.• Use a jigsaw to cut out the stator mould byfollowing the inner circle and then the outer shapeincluding the lugs. It may be necessary to drill entryholes to get the saw blade through the plywood.Drill any such holes outside the inner circle andinside the outer shape.The central island and outer surround will both be usedlater for moulding the polyester resin casting. Theiredges should be as smooth as possible. If they havecavities then fill them and sand the surface smooth.The stator-shaped piece left over (with the mountinghole marks) will be the exact shape of the finished stator.It will come in useful as a dummy when drilling themounting holes into the supporting lugs and in the statorcasting itself.Wiring exit holes• Replace the surround onto the lid, and drill two3/4" holes in the lid to allow for the wiring toemerge from the mould. These exit holes will floodwith resin. If you can form them into a smoothconical shape (perhaps using a tapered reamer),then this will facilitate removal of the lid withoutdamage to the wiring. The wiring will emerge rightat the stator edge, well clear of the magnet rotoredge. I recommend positioning these holes centresabout 1+1/2"[30 mm] away from, and to the left ofthe right hand mounting holes.Screw the mould to its base• Place the mould surround onto the base correctlyand screw it down, using different holes (not theones you drilled through the lid). Use the lid holesto position the central island on the base and thenscrew that down too. Cover the screw heads withpolish and/or tape to prevent flooding with resin.• Apply a fillet of silicone sealant to the innercorners, and polish all exposed surfaces of themould: surround, island, lid and base generously sothat the polyester resin will release. Apply plenty ofpolish to the wiring-exit holes. Run a thin bead ofsilicone around the rims of the surround and islandto counteract resin leakage.LIDMOULDBASELOCATING HOLES
  25. 25. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 25Hugh@scoraigwind.co.ukCasting the statorMaterialsQuantity Material3lbs[1.4 kg]Polyester resin (premixed with accelerator)casting resin or fibreglass resin in liquidform. Peroxide catalyst to suit.2.5 lbs.[1.2 kg]Talcum powder3 x 18"[1 x .5 m]Fibreglass cloth or chopped strand mat(1 ounce per sq. foot) or [300g per sq. metre]20 Wood screws 1 1/4" [30 mm]Before you start, read through the instructions and besure you have everything to hand including resin, talcumpowder, paint brush, fibreglass cloth, coils pre-wired,and screws to clamp the mould together.Cut two sheets of fibreglasscloth (or chopped strand matwill do) to fit inside themould. You can use the off-cut piece of 1/2 [13 mm]plywood as a template for thecloth. Mark the shape with afelt pen and then cut slightlyinside the line so that yourcloth will lie in the mouldcomfortably. Make provision for the wires where theyexit the mould. Some small extra pieces of cloth can alsobe useful for strengthening the lugs (see later).Dry runGo through the process of assembling the stator as a dryrun without resin just to check that everything fits andthere will be no hold-ups when the resin is going into themould.Putting it togetherWhen all is prepared, you can get out the polyester resinand start the job. Wear latex gloves to protect your skin.Take great care not to splash resin in your eyes. This jobshould be done in a well-ventilated area to disperse thesolvent fumes. Cover the workbench with newspaper toprotect against spilt or overflowing resin.• Mix 1/2lb [200 grams] of resin with 1/2 teaspoon [3cc] of catalyst. Use no talcum powder at first. Youcan use pigment if desired. Mix very thoroughly buttry to avoid stirring in too much air. Use the mixedresin immediately. If you delay a few minutes it mayheat up in the pot, and become useless.• Paint some of this resin mixture onto the lowersurface of the mould. Do not paint so vigorously thatyou remove the polish. Lay one sheet of fibreglasscloth onto the painted surface, and saturate it withmore resin. Use a poking motion of the brush toremove air bubbles.• Slide the pre-wired coils into place, making sure thewires are positioned correctly for the exit holes in thelid.• Pour the remains of the liquid resin mix over thecopper coils so that it soaks in between the wires.• Prepare another resin batch in the samecontainer, using 1 lb. [400 grams] of resin and 1.5tsp. [6 cc] of catalyst. Mix the catalyst in carefully,and then add about 11 lb. [400 grams] of talcumpowder. Mix again.• Pour this mix in between the coils and around theedge.• Bang the mould to encourage air bubbles to rise.Add pieces of fibreglass to the lugs forreinforcement, and poke them to dislodge bubbles.• Add further resin/talcum powder mixes untilthe mould is full to the brim.• Apply the second sheet of fibreglass cloth. Paintresin onto the top surface of the cloth. Poke it toremove bubbles. Clean the paintbrush before theresin sets.• Place the lid onto the mould, carefully threadingthe wiring through the two holes as you do so. Screwthe lid down firmly. Wipe up any resin overflowingfrom the casting. Take care that the screw heads donot fill with resin, making it hard to remove themlater. You can fill them with polish, grease orsilicone as a protection.• Mop up resin seeping out from the mould at theedges and through the wiring exits. Tighten thescrews again.Keep the mould in a warm place for a few hours. If theresin shows no signs of setting, then heat the mould infront of a radiant fire for a few minutes to kick-start thereaction. It is normal for the resin casting to heat upslightly once the resin begins to cure.200gRESINCATALYST3CC400gTALCUMPOWDER200gSHAPE OFCLOTH
  26. 26. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 26Hugh@scoraigwind.co.ukRemoving the casting from the mouldWhen the resin is fully hardened, you can dismantle themould. Remove all the screws. Prise the layers of boardapart in several places. Use hammer blows to break thebond between the boards and the casting. Take specialcare in the area of the wiring exit holes to avoiddamaging the insulation of the flexible tails.The magnet-positioning jigMaterialsPieces Material Length Width Thick1 Hardboardor plywood12" [300] 12" [300] 1/4" 6]The magnet layouts are different for the two versionsEnglish and Metric.The drawing on the next page shows the magnetpositions drawn to scale. There is only room for 1/4of the magnet rotor on the page, but you can still usethis drawing to make the magnet-positioning jig.Use this page or a photocopy of it to mark out themagnet positions on a piece of board as describedbelow. Check that the dimensions are accurate andnot scaled up or down by mistake.• Mark the centre of the board.• Draw two circles with radius 2"[50 mm] and4"[104 mm] respectively.• Draw two lines through the centre of the circlesat right angles to each other.• Align the drawing exactly on each quarter of thejig and mark the corners of each magnet with acentre punch or sharp nail.• Draw lines connecting the punch-marks, and cutalong the lines to create the jig. Use a jig-saw(US = sabresaw) or a bandsaw.• Check with a magnet for a free sliding fit.You will also need 1/2" [12 mm] holes on the 2"[50 mm]radius centres to locate the jig during use. I recommendyou just use two bolts to do this, so two holes aresufficient. I recommend using a small pilot drill first toestablish a reliable centre, followed by a 1/2" [12 mm]drill to fit the 1/2"[M12] bolt. Also drill the index hole tohelp keep track of the magnet pole positions.The finished jig looks like thisMARK THE CORNERSWITH A PUNCH
  27. 27. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 27Hugh@scoraigwind.co.uk4"2"1"2"3046104 mmRADIUS OF ARCTEMPLATE FORMAGNET POSITIONINGJIG50 mm
  28. 28. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 28Hugh@scoraigwind.co.ukMaking the two rotor mouldsMaterialsPieces Material Length Width Thick4 Floor board 16" [400] 16" [400] 3/4" [19]2 Plywood 6" [158] 6" [158] 1/2" [10]2 Hardboard 16" [400] 16" [400] 1/8" [3 ]4 Bolts,nuts+washers3"[70 mm]1/2"[12 mm]4 ScrewsSiliconesealantWax polishThe magnets are mounted on 5/16" [8 mm] steel platesthat have been drilled for mounting on the wheel-hub.We embed the magnets in resin to support them fromflying off and to protect them from moisture that wouldcause corrosion. There is one mould for each rotor.Index holeIt is a good idea to also drill the index hole for eachmagnet plate in each mould and in the jig, taking care toensure that everything is assembled the right way up.This will keep all the magnets correctly aligned.Parts of the mouldsMake the base ofeach mould fromthick board with asmooth finish, (thesame as the statormould base). Cuta square 16" x 16"[400 x 400 mm],mark the centre,and draw a circle 61/4" [155 mm]radius to help youposition thesurround on it.Place the steel diskat the exact centre of the base, and drill one or two 1/2"[12 mm] holes, and the index hole through holes in theplate. Counterbore the holes from the underneath toaccommodate the heads of the bolts.These bolts will later be used for positioning the steelplate, jig and island. Use the steel plate to guide the drill.The surrounds are also 16" x 16" x 3/4" [400 x 400 x 19mm] boards with a 12 1/2" [310 mm] diameter hole cutin it, to form the edge of the rotor casting.The islands are made from 1/2" [10 mm] plywood.They keep the resin off the central portion of the steeldisks where the mounts will be. The island diameter is6" [158 mm](same as the stator-mould island). Again,each island needs to have holes at the correct positionsto centre it on top of the steel disk.Finally you will need lids for the moulds. Cut these outthese from 16" x 16" x 1/8" [400 x 400 x 3 mm]hardboard or anything thin and slippery. Drilloversized holes to fit over the nuts on the two bolts thatsecure the island.Fill and sandpaper any cavities in the edges of theboards where the resin might penetrate and stick.Screw the surround to the base, and run some siliconearound the join. Coat the surfaces with wax polish,including the island (all over) and the lid. Be liberal withpolish on the inside of the surround, and the outside ofthe island. Cover any screwheads with polish to facilitatedisassembly later.SURROUNDISLANDBASE1/2" [12 mm] HOLES12 1/2" [310] OD CIRCLE
  29. 29. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 29Hugh@scoraigwind.co.ukCasting the rotorsPreparationMaterialsPieces Material Diameter Thick2 Steel plate disks 12 " O.D.[300 mm]5/16"8 mmQuantity Material2.5lbs[1 kg]Polyester resin (premixed with accelerator)casting resin or fibreglass resin in liquidform. Peroxide catalyst to suit.2.5 lbs.[1 kg]Talcum powder3 x 18"[1 x .5 m]Fibreglass cloth or chopped strand mat(1 ounce per sq. foot) or [300g per sq. metre]24 Magnet blocks 2 x 1 x 1/2" grade 35 NdFeB[46 x 30 x 10 mm grade 40 NdFeB]Pieces of steel, spanners etc to load the lids.Cut out two disks of fibreglass cloth. Overall diameteris 12" [300 mm] and cut a central hole about 6 1/2" [170mm] diameter.Check that the rotor disks have all the necessary holesdrilled, and the front disk has tapped holes ready for thejacking screws.Just before casting the rotors, sand any mill-scale offthe area where the magnets will sit, and clean them toremove any grease.Place the disks onto the two positioning bolts. Thesanded side should be uppermost and the index holesshould be aligned.Handling the magnetsThe Neodymium Iron Boron blocks are magnetisedthrough their thickness so as to produce a north pole onone face and a south pole on the other. North and southpoles attract each other. North repels north and southrepels south.The magnet blocks are very strongly attracted to eachother, and to steel. Hold onto them very tightly withboth hands while handling them, or they will fly out ofyour grasp unexpectedly, and may break or causeinjuries. Most people are taken by surprise and manyhave pinched fingers as a result.Magnets also pose a real threat to magnetic media suchas credit cards, sim cards, floppy disks etc. They candamage watches and cameras. Keep the magnets andthe media apart. Remove vulnerable items from pockets.Store magnets on a shelf until you need them.Dry runBefore starting to mix resin for the rotor castings, try adry run of assembly. Place the magnet-positioning jigonto the two M12 bolts. Take magnet blocks from thestock one by one, and place them onto the steel plate.Hold each block with both hands and slide it into placeas far as possible before releasing it.Checking for magnet polarityThe magnets poles alternate north-south-north aroundthe circle. Therefore each block has to be the right wayup.Each time a magnet block is placed, hold it above itsneighbour just previously placed. It should berepelled. If it is attracted, then turn it over and try again.If it is repelled then place it into its slot without turningit over again. This will ensure that it has differentpolarity from the previous block. Check all the magnetsin position periodically with a magnet in your fist. Yourfist should be alternately attracted and repelled as youprogress around the circle. Hold on tight!When it comes to fitting magnets to the second disk youmust ensure that the magnets opposite the index markwill be of opposite polarity. This will ensure that themagnet rotors will attract each other.When you are satisfied that everything is to hand andthat the magnets can be safely positioned, it is possibleto start mixing the resin.Putting it togetherMix 1/2 lb. [200 g] of resin with 1/2 teaspoonful [3 cc]of catalyst.Paint this mixture over the area of steel where themagnet blocks will lie, and allow some to run over theedge of the steel disk (already in the mould).Fit the magnet-positioning jig, and insert the magnetsto each rotor casting in turn, removing the jig once theyare all in position.Place the islands onto the bolts. Clamp them downonto the disk with 1/2" [M12] nuts and washers toprevent resin from leaking under them.EACH BLOCK HASA N AND A S POLEN AND S POLES ATTRACTEACHOTHERPOLES WHICH ARE THE SAMEREPEL EACH OTHER
  30. 30. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 30Hugh@scoraigwind.co.ukIf the liquid mix isstill usable, addtalcum powderto it and pour themix into the spacesbetween themagnets.Mix another 1 lb.[400g] resin with 11/2 tsp. [6 cc] ofcatalyst and then300 g of talcumpowder and pourthis mix in next.Continue to mixand pour resinuntil the level risesto the top of themagnets. Paintresin over themagnet faces.Take care to avoid trapping air in the space aroundthe edge of the steel disks. Use vibration to dislodgebubbles and settle the resin mix.When the resin fills both the moulds and has settled outmost bubbles, lay the fibreglass cloth disks on top,taking care to centralise them. Paint the cloth with resin.Finally lay on the hardboard lids. Clamp the lids downby placing steel objects such as spanner, nails etc ontothe surface of the lid. The magnets will pull them downand squeeze the resin layer to a minimum.Monitor the curing process, and adjust the temperatureas required, just as with the stator casting.To extract the rotors, first prise off the lids, remove theM12 nuts and bolts, and knock the rotors out of themoulds. Finally knock the island out from the centre,through the 2 1/2" [65mm] hole in the steel plate.Do not use violent blows to release the casting in caseyou break the resin or a magnet. Use persistent tappingall around the edges and be patient.FURLING SYSTEM THEORYWhy furl?The power in the wind is proportional to the cube of thewindspeed, so if the windspeed doubles, then it is eighttimes as powerful. We could design for the highestwindspeed which could ever happen and harness itspower, but then for 99.9% of the time our wind turbinewould be under-used and probably not very efficientbecause it would have a huge, heavy alternator andrelatively tiny blades.If the windspeed increases beyond a certain point thereis a danger of overload. The alternator and diodes mayoverheat, the blades may overspeed or the side loadingon the mast or tower may be too high. To prevent thesethings from happening, we fit the turbine with a furlingtail.How the furling tail worksThe wind thrust on the rotor blades is indicative of theamount of power being captured by the machine. Whenthat thrust reaches a certain level, and the wind is gettingstronger, we want to prevent the power increasingfurther. Ideally we would like to continue producing fullpower in higher winds, while avoiding overload.YAWINGMOMENTLIFTFORCEON TAILRESTORINGMOMENTISLANDMAGNETBLOCKSJIGMOULDFIBREGLASSCLOTH DISKLID
  31. 31. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 31Hugh@scoraigwind.co.ukWe build the wind turbine off-centre, so the wind thrust(centred on the alternator) is always trying to turn themachine away from the wind. If it turns away at anangle to the wind, this reduces the frontal area and limitsthe power it can capture. The trick is to make it face thewind when it needs to and to turn away by the rightamount at the right time.The alternator is offset so that the wind thrust acts at a5"[125 mm] radius from the centre of the yaw bearingon which the whole machine swivels to face the wind.This means that the thrust creates a yawing moment ortorque about the axis of the yaw bearing. The windthrust is always trying to turn the blades away from thewind.In normal operating windspeeds, the force of the windon the tail counteracts the yawing moment. When themachine tries to yaw out of the wind, the tail swings intoa position where it produces a lift force. That lift forcecreates a restoring moment which balances the yawingmoment and the machine sits there in equilibrium. Wedeliberately set the tail at a slight angle to the sideopposite the alternator offset so that the equilibrium isachieved with the blades squarely facing the wind andcatching the maximum power.Controlling the thrust forceAs windspeed increases, the thrust increases, and sodoes the yawing moment. However, the lift on the tail isalso increasing and so the equilibrium of forces keeps theblades facing the wind.The clever part of the furling design is in the way the tailis mounted. When the lift force reaches a certainmagnitude, it moves the tail into a new position. In thisposition the blades can turn away from the wind. Thethrust force is thereby reduced and a new equilibrium isestablished.We could use a spring and a hinge to construct a tailmount that yields in this way. But experience has shownthat springs vibrate, corrode and break. Instead we usean inclined hinge system which forces the tail to rise as itswings to the side. The weight of the tail itself brings itback down into the normal position. We can control thewindspeed at which furling takes place by making thetail heavier or lighter.TAIL MOVEMENTWINDDIRECTIONROTOR BLADES ARE NOW FACING OFFAT AN ANGLE TO THE WINDPLAN VIEWOFFSET = 5" [125 mm]WIND THRUSTYAWINGMOMENTBLADESTAILYAWBEARING
  32. 32. How to build a wind generator - the axial flux alternator windmill plans - May 2003 version © Hugh Piggott page 32Hugh@scoraigwind.co.ukFabricating the tail hingeMaterialsPieces Material Length Diam. Thick1 Steel pipe1 " nominalbore8"[200 mm]1 5/16"[33.4]overall1/8"[3 mm]wall1 Steel pipe1 1/4"nominal bore4[1200mm]1 5/8"[42.2]overall1/8"[3 mm]wall1 Steel pipe1 1/4"nominal bore6"[150 mm]1 5/8"[42.2]overall1/8"[3 mm]wall1 Steel disk 1 5/8"[42.2]minimum5/16"[8 mm]Pieces Material Length Width Thick1 Steel plate 4"[100]2 1/4"[56 mm]3/8"[10 mm]1 Steel bar 12" [300] 1 1/2"[30] 5/16 [8]The tail hinge is made in thesame fashion as the yawbearing. It consists of a 1 1/4"nominal pipe slipped over a 1"nominal pipe.These pipe sizes are used inboth the English and theMetric versions.The smaller, inner pipe is to bewelded to a shaped piece of3/8" [10 mm] plate. The otherside of the plate is welded to theyaw bearing. The resultantangle of the inner pipe is 20degrees to the vertical.You can cut this plate out from 4" x 3/8" [100 x 10 mm]flat bar. The 20-degree angle is achieved by making oneside of the plate 2 3/16" [57 mm] long and the other 3/4"[20 mm] long.Weld the plate onto the 1" pipe first, and then weld itonto the yaw bearings as described below.The hinge must be welded onto the yaw pipe in adiagonal position, as seen from above. The anglebetween the pipe and the rotor plane is 35 degrees in thisplan view.I find that the easiestway to achieve this 35-degree angle is to setthe yaw assembly upon the bench with thealternator-mountingbracket at 55 degreesto the horizontal.Then I sit the tailhinge pipe and platevertically on top of theyaw tube and weld itthere.Apply plenty of weldsat both sides of thesteel plate. The tailwill put some criticalloads on this part.Good quality weldingis essential here.35 degrees48" [1200 mm]"INCH AND ONE QUARTER" NOMINAL BORE STEEL WATERPIPETAIL HINGEOUTERPIPENOTCH INOUTERPIPETAIL BOOM4"[100]6"[150]WELDEDFABRICATION110 DEGREESFIND POSITIONS OFNOTCH CUT LINES BYFITTING TOCOMPLETED MACHINE20DEGREES1 1/4" [30 mm]END OF TAIL BOOM2 3/16"[56 mm]4"[100]3/4"[20]1 3/8"[60.3]TAIL HINGE SIDE VIEWYAW PIPETAILHINGEINNERPIPE3/8"[10mm]STEEL20 DEGREES8"[200 mm]55 DEGREESWORKBENCH35DEGREESVERTICALTHE SET UPFORWELDINGPROP UP THEALTERNATORBRACKET AT 55DEGREES TO THEWORKBENCH LEVEL10 1/4"[260 mm]

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