[Greg Needel]

While many people in this thread are on the right idea, the real trick to this is to design a gearbox based on the current draw. Assuming that you are looking to get maximum torque you should design your gearbox to pull just under 40 amps at maximum torque. This requires you to know the approximate coe of friction with the playing field surface, determining motor torque based on amperage, the approximate gearbox Efficiency, and your normal force.

Assuming a flat surface:

Max Force= Force friction = (Coe of Friction) * (total Weight)

Force = (Torque at the wheel) /

Torque at the wheel = (Torque at 40Amps)*(Gear Ratio)*(Gearbox Efficiency)

So substituting Forces you get:

(Gear Ratio)/ (Wheel radius) = ((Coe of Friction) * (total Weight))/ ((Torque at 40Amps)*(Gearbox Efficiency))


Standard Efficiencies for drives:
Chain drive 95-98%
Spur Gears 95-98%
Bevel Gears 90-95%
Worm Drive 40-70%
Planetary 80-90%

This will give you the optimization of pushing force and gear ratio for a drive train which you can then use to find your maximum speed. If you want to have a greater maximum speed you can decrease the ratio at the cost of torque. Design is all about tradeoffs but this is a good place to start.