6 CIM robo-rio brown out

[GeeTwo]

Originally Posted by Chak

It would be interesting to see whether a 3 CIM drivetrain would work under certain situations, or if 3 CIM drivetrains are just not possible.

Originally Posted by Ari423

I can't speak to the battery resistance part. I can say, however, that there's more to it than just 3 CIM motors. It also has to do with robot weight, track CoF, gear ratios in the drive gearboxes, lengths and size of wire between the battery and motors, and a bunch of other stuff.

That's pretty much the high-level story. 3-CIM-per-side drive trains are not, if managed properly, the kiss of death. With proper current and voltage monitoring, it is certainly possible for software to truly "brown" out the motors (by reducing the supply percentage or cutting off a motor) rather than "black" them all out at the same time as the RoboRIO shall do. This is a "black" out in that all of the PWM and CAN motor controllers are disabled at the same time; a brown out is when voltage is limited to prevent a black out. The "black out" prevented by the built-in "RoboRIO brown out" is only enough to prevent a RoboRIO shutdown and reboot. While I cannot tell you that it hs never happened, I do not know of this happening to a cRIO starting with a fresh, healthy battery in a 3-minute match.

The real question is whether, after writing "true brown out software" there is enough of an advantage to justify the weight, expense, and gears of 3-CIMs vs 2-CIMs per side.

Edit (ninja'd):

Originally Posted by Joe Ross

In most cases, a brownout condition will turn off your motors for a fraction of a second, and then everything will recover. You may not even notice most brownouts.

In our experience, you will definitely notice. This is what happens:

1. The current draw causes the RIO to "brown out" the motors.
2. The voltage recovers.
3. The system restores the motors.
4. The motors draw inrush current.
5. Return to step 1.

This results in a very distinctive "stutter" at about 15-20 jitters per second that gets the robot nowhere fast.

Please don't construe this as disagreeing with any of Joe's mitigation strategies! (Well, in #7, I'd say tanks rather than cylinders. Are you reading, IndySam, Lil Lavery, and BBray_T1296?)