GEARS:
Gears too are extensively used in industry, automobiles and domestic applications.
Efficiencies can be similar to belts, in the order of 97% for a single reduction provided
alignment, bearings, gear tooth form and lubrication are good. To keep losses low and
efficiency high the teeth of mating gears MUST be parallel, clean and the backlash
(clearance between engaged teeth) correctly adjusted. If not accurately set up, gear losses
can be very high. The correct backlash for the precision gears commonly used in model
solar cars is in the order of 0.08 mm. Operating with less backlash than this will increase
losses. Operating with slightly more has very little effect, but too much more will
increase losses. To maintain high efficiency your design must ensure accuracy is
maintained when gear changes are made. Do not forget that during competition, gear
changes must be made in the field quickly while the team is under pressure.
To reasonably match panel output power to motor power requirements as the sun level
changes, several ratios will be required. If you want a close match at every operating
point as many as 8 or more ratios may be required which can be expensive if precision
gears are used. If cheaper, non-precision gears are used, take care the power losses are
not too high and the gears have sufficient strength. Many cars have stripped gears during
racing.
NOTE: The use of an electronics system probably removes the need for gear changing.
DIRECT DRIVE:
Direct drive whilst always a great method has not been included in previous design hints
due to the lack of appropriate hardware. It now appears to be a viable option and has been
added.
Direct drive ie. a wheel mounted directly onto the motor shaft has always been worthy of
consideration, but difficult to execute. I first saw a car using this system on a car at the
2008 Hobart National event.
With a small diameter wheel, a good electronics system, a motor capable of supplying the
high torque required and a solar panel with characteristics that suit the electronics and
motor, (See Solar Panel) direct drive is now a real possibility.
After seeing this car run in Hobart I entered appropriate data into the Mathematical
Simulation which predicted very competitive times from a car using that set up.
The gains from using a direct drive include, an approximate power increase of 6% due to
elimination of gear losses, reduction in weight and complexity by eliminating gears and
simplified construction of chassis. There may be a weight penalty involved in using a
suitable motor. You as designer must consider