Torque

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Torque

  1. 1. Torque this! What is torque?
  2. 2. A BLance needs to climb the Pyrenees. His only options are fixed gearbikes. Which one should he choose for the mountain climb? Why?
  3. 3. Torque (Rotational Force) Torque is the effect of a force applied on a body at some distance from the axis of rotation of that body (c.w. or c.c.w.). Ex: Torque wrench or large pipe wrenches.Torque = Force * Lever arm (length)Unit of measurement: English = Ft lbs SI = Newton meters
  4. 4. How is it calculated? As you apply a force to any point on a lever arm (FxL) it gives you a Torque value that is “in waiting” at the point of rotation. If you try to “feel” or re-apply that torque at any other lever distance from the axis of rotation, the torque is the distributed along the lever length (L). The shorter the Lever or smaller the sprocket, the greater the Force that is applied from Torque.
  5. 5. In each case, the same torque gets “loaded” into the drive hub at the front sprocket. But A the torque then gets re- B applied through the length of lever arm. Depending on the length you’ll get some kind of Force (T/L=F)Because Lance loads the same amount of torque into the drive hub thesmaller front sprocket distributes the torque less, so more force is“conserved” and is applied to the chain.
  6. 6. Force Transformers – Belt Drive Drive DrivenForce: Since the two pulleys are connected by a common belt the Force In = Force OutLever Arm: The distance from the center of the pulley to the outside rim (radius).Angular Speed: If the output pulley is twice as big as the input pulley, then the output pulleywould only make ½ revolution for every revolution of the input pulley.Torque: Torque in = Fin x Lin Torque out = Fout x LoutMechanical Advantage = Torque out / Torque inMechanical Advantage: Since the Forces of the two pulleys are equal, then the lever arm(radius) of the pulleys must determine mechanical advantage.
  7. 7. Torque Transformer -Gear Drive Drive =18 Teeth Driven =24 Teeth1. Force: Since the gears are directly connected the force from the drive gear is directly transferred to the driven gear. In other words Force In=Force Out2. Gear Ratio: Drive (input) gear = 18 teeth: Driven (Output gear) = 24 teeth Gear Ratio = (Driven Gear / Drive Gear) = 24 / 18 or = 1.33 to 13. Lever Arm: The distance from the center of the gear to the gear tooth (radius).4. Angular Speed: If the drive gear makes one revolution, the output gear would make ¾ (.75) revolution). If the input gear was spinning at 1000 rpm the output gear would be spinning at 750 rpm5. Torque: Torque in = Fin x Lin Torque out = Fout x Lout6. Mechanical Advantage: Determined by the Gear Ratio ( or ratio of the radii)
  8. 8. A bicycle is a combination of a gear drive and belt (chain) drive system 200 N 1200N•10cm=12,000N•cm of torque at driven hubCalculate for both: 6000N•cm/5cm=1200N1) Torque at hub of 10 cm (force transferred) 20 cmdrive gear2) Force transferredfrom drive to driven Pedal Length = 30 cmgear 200 N3) Torque at hub ofdriven gear 6000 N•cm of Torque in 20 cm 10 cm each case: (200N•30cm) Note: 200 N = about 45 lbs of force
  9. 9. Torque vs. Speed Greater Torque Less Speed Less Torque Greater Speed
  10. 10. Basso’s Challenge If the input (drive gear) is spinning Clockwise at 20 rpm how fast and what direction is the output gear spinning? N-is the number of teeth http://auto.howstuffworks.com/gears.htm http://www.howstuffworks.com/transmission.htm http://www-education.rec.ri.cmu.edu/multimedia/cgr.shtml

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