Materials Needed:
- Motor
- 3V power source (battery)
- 1 small pulley (motor axle)
- 3 larger pulleys (output axle see setup)
- Cardboard or foamboard (chassis)
- Axle shaft (output axle)
- Rubber band or belt (pulley)
- Axle bearings (see setup)
- Hot glue or tape
Procedure: (see Figure 16)
- Build the test transmission as shown in the setup figure
(mount the motor to a piece of material so it
can be moved to align with the different pulleys
and stretch the belt drive).
- Move the beld to different pulleys and see the results
of the different ratios.
- Which ratios give the highest speed?
- Which ratios make the output axel easiest to stop with
your finger?
- Try different bearings on the output axle.
- Does the bearing material affect the speed or ease of
stopping the output axle?
- Try adding or removing weight from the output shaft to
see the efect on the system.
Notice how flat rubber bands tend to crawl up the edges of a pulley -
try a "crowned" pulley (convex profile) as shown in Figure 16. It is
counter-intuitive, but does work, and is used often in machines.
Figure 16: Transmission investigation setup
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Observations:
Building a car without any knowledge of the best transmission ratio is
risky because the car will not perform to its full potential (if it moves
at all). This investigation uses a belt and pulley system, but the ratio
of the pulley diameters applies to all the other types of transmissions
as well (gears, friction drive). You can use this type of investigation
in your final car as well to arrive at the best transmission for your
design.
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