Torque this!

What is torque?By the end of today you should be able to:

•Define Torque•Make a basic Torque calculation

Lance needs to climb the Pyrenees. His only options are fixed gear bikes. Which one should he choose for the mountain climb? Why?

A B

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•lb SI = N•m

How is it calculated?

As you apply a force to any point on a lever arm it gives you a Torque value, which is a twisting value measured at the point of rotation. (T=FxL

In order to feel, use or re-apply that torque, a lever arm or any length must be attached and the torque is the distributed along the lever length, thus producing a force (F=T/L).

The shorter the Lever or smaller the sprocket, the greater the Force that is applied from Torque.

In each case, the same torque gets “loaded” into the drive

hub at the front sprocket. But the torque then gets re-

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 the smaller front sprocket distributes the torque less, so more force is “conserved” and is applied to the chain.

A B

Force: Since the two pulleys are connected by a common belt the Force In = Force Out 

Lever 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 pulley would only make ½ revolution for every revolution of the input pulley. 

Torque: Torque in = Fin x Lin Torque out = Fout x Lout 

Mechanical Advantage = Torque out / Torque in

Mechanical Advantage: Since the Forces of the two pulleys are equal, then the lever arm (radius) of the pulleys must determine mechanical advantage.

Drive Driven

Force Transformers – Belt Drive

Torque Transformer -Gear DriveDrive =18 Teeth Driven =24 Teeth

1. 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 Out

2. Gear Ratio: Drive (input) gear = 18 teeth: Driven (Output gear) = 24 teeth

Gear Ratio = (Driven Gear / Drive Gear)

= 24 / 18 or = 1.33 to 1

3. 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 rpm 

5. Torque: Torque in = Fin x Lin Torque out = Fout x Lout

6. Mechanical Advantage: Determined by the Gear Ratio ( or ratio of the radii)

A bicycle is a combination of a gear drive and belt (chain) drive system

10 cm

200 N

20 cm

200 N

20 cm 10 cm

Pedal Length = 30 cm

Calculate for both: 1) Torque at hub of drive gear2) Force transferred from drive to driven gear3) Torque at hub of driven gear

Note: 200 N = about 45 lbs of force

6000 N•cmof Torque ineach case:(200N•30cm)

6000N•cm/5cm=1200N(force transferred)

1200N•10cm=12,000N•cm of torque at driven hub

Greater TorqueLess Speed

Less TorqueGreater Speed

Torque vs. Speed

http://auto.howstuffworks.com/gears.htm

http://www.howstuffworks.com/transmission.htm

http://www-education.rec.ri.cmu.edu/multimedia/cgr.shtml

Basso’s Challenge

If the input (drive gear) is spinningClockwise at 20 rpm how fast and what direction is the output gear spinning?

N-is the number of teeth