To further assist understanding the photograph below shows testing set up on the car
Photon Cruncher MK IV.
PHOTON CRUNCHER MK IV BEING PUSHED ON STRAIGHT TRACK
SECTION NOTE ADDITIONAL WEIGHT ON SOLAR PANEL.
Determining the force to roll can be done with a spring balance , but take care that the
balance you use maintains accuracy when horizontal. Otherwise a cord around a pulley to
keep the spring balance vertical will be required. An option is tilting the surface the car is
on, measuring the height it is lifted to just roll and calculating the force acting down the
ramp due to gravity.
You should note that for this model we have assumed the wheel load to be constant as
the car runs around the track. This is not exactly true. The wheel load is determined by
the component of the gravity force which is normal to the track surface. This changes
depending on position on the track – when the car is on a slope it is reduced slightly (see
FIG 2). Since the hills are short compared to the track length and the slope fairly gentle
we did not go to the trouble of including this change in the model.
There is also weight transfer to the outside wheels when cornering this too has been
ignored.