APPENDIX B: TRANSMISSIONS FOR SOLAR CARS
The following is a simplified resume of transmissions typically used in model solar cars.
It had previously been limited to gear and belt drives, as they were and still are the most
commonly used systems in model cars, but has now been expanded to include direct
drive.
Please refer to standard Engineering texts for more detailed information.
BELTS:
Belts are used extensively for various drives in industry, automobile and domestic
applications. Power transmitted can be high with the use of multiple belts.
SOME ADVANTAGES OF BELTS:
- High efficiency up to 97% possible (Marks Handbook for Engineers)
though may be difficult to obtain when scaled down to model solar car
sizes and powers. - Large centre distance between shafts possible.
- Will tolerate misalignment much better than gears. (Consequently ratio
changes are easier than gears). - Pulleys much easier and cheaper to make than gears (meaning that many
ratio changes can be available at lower cost).
SOME DISADVANTAGES OF BELTS:
- Always run with some slip or creep so will not guarantee constant angular
velocity or angular velocity ratio equal to the pulley diameter ratio. - Can slip significantly if overloaded.
- Can break.
BE CAREFUL: Belts on model solar cars present some special problems. When scaling
down to the very small sizes and powers in the model car we cannot use ordinary belts.
Our tests have shown that belt material is critical to success.
· We tested ‘O' rings and found they are very poor belts. The strength is great but
efficiency is low, probably because of their stiffness, they waste a lot of energy
in flexing the ‘O’ ring.
· Tape recorder drive belts were better but preliminary tests show they are only
about 82% efficient.
· Rubber bands when tested gave poor efficiency apparently because of creep they
stretch easily and this stretch represents lost energy.Remember, belts drive by friction, so tension is important. Our tests showed very little
difference in losses as belt tension was increased. Keep belts tight. Pulley material and
contamination with oil, water, etc. will change frictional coefficients and consequently
degrade power transmission.
We have not tested toothed belts but expect them to be similar to “O” rings because of
their stiffness.