Drive Train Calcs - Not trusting my results

[Nemo]

Originally Posted by Gregor

At about what speeds are these according to your calculations?

It is highly dependent on several factors. Let's say I assume the following:
CoF = 1.2
Drive efficiency = 0.80
Carpet-wheel efficiency = 0.93
Enough resistance to cause voltage to drop to 7.8 V / 6.7 V for 4/6 CIM drive
Charged battery voltage = 12.8 V

4 CIM is traction limited at about 11 ft/s
6 CIM is traction limited at about 14 ft/s

Change any of the conditions I listed, and you get an appreciable change. I encourage you to download the spreadsheet and start messing with the numbers along the left side.

In practice, we had to gear our drive closer to 9 ft/sec to get the tires to spin from a stop using 4 CIM's, Versawheels, and 1 stage Vex gearboxes plus a chain stage (we have since gone to ballshifters). I can play with numbers to make the spreadsheet report that 9 ft/s result, but I don't know which of the factors listed above is off by the most. That's why I'd like to put together some testing in the fall.