paper: 4 CIM versus 6 CIM theoretical calculations

[AdamHeard]

Originally Posted by GeeTwo

I agree that there would not be a problem while driving the robot, but there might be an issue when on blocks. I figure (using Vex's numbers and a bit of linear extrapolation) that putting a CIM and mini-CIM nose to nose at 12V would reach a free speed of 5507 rpm, at which point the mini-CIM would be drawing 7.9A, 46W of mechanical power would be transferred, and the CIM would be generating 1.6A. The CIM would switch from consuming to generating current at about 5442 rpm, so probably even a gearbox on blocks would provide enough drag. Of course, both the CIM and mini CIM free speeds have a +/- 10% variation, so if you put a fast mini and a slow CIM together, you might have some issues when running the motors with the robot on blocks.

This wouldn't cause any issues, you'd just be pumping some current back to the DC bus and everything would be fine.

[GeeTwo]

Originally Posted by AdamHeard

This wouldn't cause any issues, you'd just be pumping some current back to the DC bus and everything would be fine.

If you didn't have motor controllers, or (illegally) put both motors on the same controller, this would certainly be the case. Are motor controllers designed to handle the reverse bias? - Oh, right. If you decide to change from 100% speed to 50% speed in a short period of time, you'll create the same situation, so they have to be designed that way. Never mind.