tyre. Tests indicate that a single 1/16”section O ring used as a tyre on a wheel of 70 mm
diameter increased rolling resistance by 0.07 Newton. To keep rolling resistance to a
minimum never use tyres on any wheel except the drive wheel. And only then if wheel
slip is a problem.
Observation has shown that an aluminium or plastic drive wheel has sufficient friction to
drive without a tyre once the car is up at speed. However at high Sun levels with an
electronics system wheel slip will almost certainly occur during starting. (NOTE: The
plastic drive wheel has about 15% less friction than the aluminium wheel so will require
a tyre at a lower Sun level if slip is to be avoided or minimised.)
Track testing has shown that the high torque output of the 2232 motor when driven
through an electronics unit results in appreciable wheel slip on initial take off in high sun
conditions.
At 90% Sun actual track testing of Photon Cruncher MK IV has shown this wheel slip
resulted in a single lap time 0.6 seconds slower than that obtained when a tyre was fitted.
(to the drive wheel only) Obviously as the Sun level drops there is a break even point
where a tyre begins to slow you down again this is because of the increased rolling
resistance a tyre causes.
2 Drive train
The car should have its gear ratio very carefully chosen to operate the motor and solar
panel combination at their most effective point for the prevailing conditions. (See section
8 ELECTRONICS for operating point description.)
You need to reduce motor speed which can be in the order of 20000 RPM down to the
wheel speed required typically in the area of 1000 to 3000 RPM depending on wheel
diameter.
Gears are the most common speed reduction system in use. Remember the power loss in
the drive train can be high if it is not accurately made and adjusted.
On a conventional axle set up i.e. a transverse axle with a wheel each end, normally only
one wheel is driven and the other allowed to run free to give differential action. If you
have both wheels locked to the axle, large power losses will be experienced during
cornering.
Refer to Appendix B, Transmissions for Solar Cars, for more details on reduction
systems.
3 Solar panel
A: General
NOTE: All data and references to Solar Panels or cells in this document are to SILICON
CELLS, as these are the only type of cell approved for use in this event. (See regulations)
Maximum dimensions and power output of your panel must conform to the requirements
detailed in the Regulations.