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# Patterns ofbuildinglegos

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And now for something completely different. This is something I wrote back in 2007 for my FLL team when teaching them basic concepts for robot design.

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### Patterns ofbuildinglegos

1. 1. Patterns of Building Legos Kyle Brown
2. 2. Acknowledgements Fred G. Martin, The Art of Lego Design, The Robotics Practitioner: The Journal for Robot Builders, v1, #2, Spring 1995 Dean Hystad, Building Lego Robots for FIRST Lego League, v1.3, available from www.hightechkids.org
3. 3. Glossary Rotary motion – motion in a circle; like a wheel spinning or an axle turning Linear motion – motion in a straight line; like your hand pushing forward Reciprocal motion – linear motion that switches direction, like a car piston Torque – the amount of force on a rotating axle (different from the speed of rotation)
4. 4. Angles 90° angle (also known as a right angle) 90°
5. 5. What’s a pattern? A solution to a commonly recurring problem If you come across the problem again, you can apply the solution again!
6. 6. Frame Building
7. 7. 2 hole plate frame Problem: How do you build a sturdy rectangular frame with holes for axles? Solution: Connect technic beams with 2- hole plates on the end. For even stronger frames use 2-hole plates on top and bottom
8. 8. Cross-bracing Problem: How do you join technic beams together so they won’t slip apart? Solution: Use cross-bracing
9. 9. EXERCISE Each team build two rectangular bases that: • Are at least two technic beams high • Won’t slip when the corners are pushed to the right or left • Are at least 1 ½ times longer than an NXT motor and at least 3 times as wide
10. 10. Basic Rotary Motion
11. 11. Stop Bushing Problem: How do you keep gears from sliding around on an axle or keep axles from sliding out of a frame? Solution: Use stop bushings
12. 12. When do you need more torque? If you need to move a heavy load or move something with a long swing distance, you need more torque Technically it’s defined as force (weight) times a distance (a moment arm). Point of rotatio force n distance
13. 13. Gear Ratios Problem: How do you make an axle move either faster (with less torque) or slower (with more torque) than a motor? Solution: Use gear ratios to gear up or *the gear ratio is the number of gear down teeth on each gear expressed as a fully reduced fraction
14. 14. Ganging Problem: How do you create gear ratios that go beyond the ratio of a single pair of gears? Solution: Gang the gears together by placing large and small gears together on the same axle See: gear ratios
15. 15. Gear Train Problem: How do you change the torque or speed of rotation between two axles? Solution: Mesh two or more gears together into a gear train See: frame building patterns
16. 16. Idler Gear Problem: How do you make two axles separated over a small distance turn in the same direction? Solution: Use an idler gear Note: Idler Gears do NOT change the gear ratios between Input and output axles!
17. 17. Exercise Using the rectangular bases from the last exercise: • Attach two wheels (one on each side) to an axle so that the wheels turn at 3/5 the speed of the drive axle For every five turns of this drive axle The wheel should turn three times
18. 18. Robot Basics
19. 19. Drive Base Problem: How do you allow your robot to have a stable base that allows both navigation and manipulation of objects? Solution: Use a separate drive base that moves the robot and attachments that manipulate objects.
20. 20. Example Drive Bases Drive bases can have 3 wheels, 4 wheels, tank treads, skids, or any combination of the above! A drive base consists of a sturdy frame with motors, controller brick , skids, casters or wheels attached to the frame
21. 21. Drive base combinations Differential Drive Tank treads Two Wheel Drive Synchro drive
22. 22. Differential Drive  Has two powered wheels plus casters or skidsSkids or casters (front, back or both) Independently powered wheels
23. 23. Building a simple caster The key is that both the wheel axle and the center axle need to swivel freely
24. 24. Differential Drive Advantages • Simple • Turns on the spot Disadvantages • May not drive straight accurately • Friction may lead to varying accuracy in turns
26. 26. Two-wheel Drive Front Wheel steering with powered back wheels Just like on a car
27. 27. Two Wheel Drive When you turn all the wheels move at different speeds • Use a differential on the back wheels You need a mechanism to turn the front wheels • Usually a rack and pinion
28. 28. Two Wheel Drive Advantages • Can carry very heavy payloads Disadvantages • Very, very complicated to build • Comparatively large turning radius
29. 29. Synchro Drive Have all the wheels simultaneously powered and turned • One motor powers the wheels • One motor turns the wheels • Use a Lego turntable to independently turn the wheels Advantage: EXTREMELY accurate Disadvantage: VERY complicated
30. 30. EXERCISE Build a robot with the following attributes: • It has a stable rectangular base that does NOT use the NXT brick as a structural member • It uses differential drive with a front caster or skid • The drive wheels turn at only 3/5 of the speed of the drive wheel motors
32. 32. Bevel Gears Problem: How do you convert rotary motion into rotary motion at a 90° angle with a 1:1 gear ratio? Solution: Use two bevel gears
33. 33. Crown gear How do you convert rotary motion to rotary motion at a 90° angle with a differing gear ratio? Use a regular gear and a crown gear
34. 34. Worm Gears Problem: How do you convert rotary motion to rotary motion at a 90° angle that is self locking? Solution: Use a worm gear with a crown gear*self locking means that the follower axle can’t move the drive axle
35. 35. Clutch Gear Problem: How do you limit the torque in a gear train? Solution: Use a clutch gear *you often want to limit torque to prevent lego pieces from breaking under strain.
36. 36. Ratchet Problem: How do you limit rotary motion to a single direction only? Solution: Use a ratchet
37. 37. Pulleys and Belts Problem: How do you connect two widely separated axles turning in the same direction? Solution: Use pulleys and belts *pulleys and belts can also be used to limit torque since the belt will slip when the torque is too high
38. 38. Belts at an Angle Problem: How do you connect two widely separated axles that are at an odd angle? Solution: Use pulleys and belts
39. 39. Linear Motion
40. 40. Rack and Pinion Problem: How do you convert rotary motion to linear motion 90° away from the rotating axle over a short distance? Solution: Use a Rack and Pinion *notice that the rack has to be able to slide on a smooth track.
41. 41. Piston Rod Problem: How do you convert rotary motion to reciprocal linear motion 90° away from the rotating axle over a very short distance? Solution: Use a piston rod Note: a Piston like this has a bit of side- to-side motion to it…
42. 42. Lead Screw Problem: How do you convert rotary motion into continuous linear motion in the same direction as the rotating axle over a short distance? Solution: Use a Lead Screw
43. 43. Scissor Arm Problem: How do you convert a small linear motion into a larger linear motion at a 90° angle? Solution: Use a scissor arm
44. 44. Exercise Build a crank-powered Lego construction to: • (1) Move a lego minifigure 1 ½ inches forward • or • (2) Move a lego minifigure 6 inches forward
45. 45. Object manipulation
46. 46. Pusher Piston Problem: How do you move an object a short linear distance? Solution: Use a pusher piston Picture shows a piston connected to a crankshaft
47. 47. Dumper How do you release one or more objects all at once? Solution: Use a gravity-fed dumper You can either rotate the dumper into position or lift it up on one end with a piston or lead screw
48. 48. Water wheel Problem: How do you release several objects from a hopper over a period of time? Solution: Use a gravity-fed water wheel
49. 49. Pincer Problem: How do you grasp an object when you have clearance on two sides? Solution: Use a pincer
50. 50. Pincer types Parallel Gripper Pinch Gripper
51. 51. Simple fork tines Problem: How do you grab an object at a fixed height and deposit it in base? e.g. how do you pick a loop up? Solution: Use a simple fork tine attachment, either powered or unpowered The simplest one is a fork directly attached to a forward-facing motor Multiple tines allow for variation in accuracy in getting to the loop. Single tines give more control but require precise navigation
52. 52. Forklifts Problem: How do you grab an object at a variable height and deposit it later at a different height? e.g. how do you pick a loop up and put it back down? Solution: Use a forklift attachment Can use either belt drive (simple) or gear drive (more robust)
53. 53. Scoops Problem: How do you relocate an object freely sliding on the board? Solution: Use a scoop or plow attachment
54. 54. Exercise Each team build either a pinch gripper or a parallel gripper • Capable of grabbing a minifigure How would you power these from an NXT motor?
55. 55. Wedge Problem: How do you separate two objects? Solution: Use a wedge to force the two apart