approximate length of full straight section). Mismatch of the guide rail of 1mm
horizontally and 3mm vertically would be the maximum expected.
Another important but seldom considered aspect of the track is its surfaces frictional
characteristics. Who cares you say, everyone should. Wheel slip due to lack of surface
grip will significantly slow your car down. (See section on wheels where tyres are
discussed) Here in Victoria where the track is painted with a flat acrylic paint, the friction
is fair. However the New South Wales track has a smooth plastic surface with the
frictional characteristics of a sheet of glass. This track is sometimes used for the National
event so you may encounter it. I have no information on other tracks but do not expect
any to be worse than the NSW track.
See Appendix P for track friction test results.
15 Construction (Build accuracy)
For the best possible performance it is critical to construct your car accurately, with
sufficient strength and rigidity to maintain alignments and clearances particularly in the
critical areas of drive train, wheels and guides. A poorly constructed car WILL perform
poorly.
For example, we have data from 2 similar cars, both about the same size, used the same
motors, gears, panel, electronics, wheels and guide system. Both had similar layouts i.e.
rear wheel steering and the same aerodynamic drag coefficient. The only difference was
weight, about 100 gm which should only give a difference of about 0.4 second in full sun.
The actual difference in full sun was 5.3 seconds. The slower car was slightly out of
alignment and could be observed “crabbing down the track”.
To help quantify the importance of accuracy consider the following. Two similar cars
being track tested at the same time. Both cars using similar motors, panels, electronics,
running gear and with similar aerodynamic drag characteristics and no steering, but one
car was running without ballast and was consequently 800 gm lighter. The lighter car was
noticeably slower. Subsequent examination revealed its axles were 5mm out of parallel.
The lesson here is that build accuracy is critical.
In the construction process, do not neglect the electrical systems. Many problems are due
to wiring, it should be colour coded, neatly laid out and secured to prevent damage due to
vibration and handling. This will make fault finding significantly easier if it is required.
All joints should be soldered then insulated if there is any possibility of shorting out.
16 Testing
You cannot do too much testing. You can however do too little as shown by the high
numbers of cars that will not complete the course or will not even run at all.