[Richard Wallace]

Originally Posted by LH Machinist

Thanks for the information. However, it doesn't make sense in my mechanical mind...using a 2 to 1 gear reduction with 4" wheels. ... Am I missing something?

Sorry, I should have expressed that a little more clearly.

I meant a 2:1 speed INCREASE from motor shaft to wheel. Effectively making a 4" wheel behave like an 8" wheel mounted directly on the motor shaft.

Here's how I did the math:

Climb height = 110 inch (2.79 meter)

Energy = height X weight = height X mass X g

Energy (Joule) = height (meter) X mass (kg) X 9.8 m/sec^2

Example: if mass is 5 lb (2.27 kg) then energy = 62.2 Joule

Maximum motor output power (assuming a full Tetrix battery) is about 15 Watt at 90 RPM -- operating at different RPM will REDUCE the power.

Time to climb = Energy / Climbing Power

Climbing Power = Motor Power X drivetrain efficiency

If drivetrain efficiency is 75% and two motors are used, then Climbing Power is 30 X .75 = 22.5 Watt. So, Time to Climb is 62.2 / 22.5 = 2.8 seconds, and climbing speed is 110 inch / 2.8 sec = 39.8 inch/sec. If 4 inch diameter wheels are used, then wheel speed is 39.8 / 4*pi = 3.2 rev/sec = 190 RPM. To match this wheel speed to the 90 RPM motor speed, the gear ratio is 190/90 or ~2.