Quote:
Originally Posted by Roboshant
What would be a safe fps for a 120 pound robot with a 6 CIM drive train?
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It depends on your driving conditions and what you mean by safe. If safe means that the chassis is traction limited so that it is all but impossible to draw more than 150A, total, you can use
JVN's latest calculator to get the answer. I leave that as an exercise, but the answer will surely be "too slow to be competitive for most FRC games and strategies."
The real question with a 6 CIM vs a 4 CIM drivetrain is "How much more torque/power can I get when running current limited?" For sake of calculation, let's assume you have a 180A current budget for your CIMs in a relatively short battle. During this time period, each CIM in a 6 CIM drivetrain will draw 30A, and each in a 4 CIM dirivetrain will draw 45A.
Checking
the CIM power curve, at 12V and 45A each CIM generates about .79 Nm of torque, and at 30A it's about .51 Nm, meaning that the 4 CIM drive train can actually generate about 0.1Nm more torque. The advantage is in power: the 2160W of electrical power consumed by each drive train is converted to mechanical energy about 7% better by 6 CIMs than 4, yielding another 160W of mechanical power.
If your mechanisms are fast enough and reliable enough and your driver good enough to make use of that power, go for it. If not, 6 CIMs just makes it a bit easier to draw too much current. The bottom line is that a 6 CIM drive train is inherently more dangerous than a 4 CIM drive train. You need to evaluate whether the danger you're causing is worth the danger you're accepting.