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Unread 12-12-2011, 15:41
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Jared Russell Jared Russell is offline
Taking a year (mostly) off
FRC #0254 (The Cheesy Poofs), FRC #0341 (Miss Daisy)
Team Role: Engineer
 
Join Date: Nov 2002
Rookie Year: 2001
Location: San Francisco, CA
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Re: Team 254 2011 FRC Code

Quote:
Originally Posted by AustinSchuh View Post
I feel the need to quote this to emphasize it. Someone on 254 this year had a huge lookup table to do just this, but, as far as I could tell, didn't filter the data. The result was a bit inconsistent, and we went back to the polynomial.

To do it really right, I want to take a victor, battery, CIM, and a dynamometer, and generate data points for various different operating points. (Use 16 speeds and 16 PWM values.) Not sure where I can get access to a dynamometer though. I have noticed that in practice, for example, if you are going forwards, and apply a tiny bit of backwards power, the entire drivetrain locks up.
If you have a CAN Jaguar and a spare motor lying around, I'd imagine you could use the Jag's current sensor as a makeshift dyno.

The drive locking up when you apply a bit of reverse power makes perfect sense given that the motor controller has an internal H bridge. When you switch directions, it's as if you are in "brake mode". This can be very useful for stopping on a dime in auto mode.