Thread: PCM Brownout
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Unread 24-02-2016, 12:24
gpetilli gpetilli is offline
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Re: PCM Brownout

It may be that your battery voltage is dropping low enough that the PCM can not generate the correct voltage to drive the solenoids. It is probably real. This year in particular with many teams not correctly adjusting gear ratios for 8" wheels, there have been lots of brown outs.

Keep in mind that the short circuit current of the CIMs is 133A per CIM (practically limited to about 90A). If you have 4 CIMs, thats roughly 400A. The battery internal resistance is about 0.022ohms so it drops 8.8V leaving only 12-8.8V or 3.2V at the input to the PDB. This is an extreme example, but you get the picture. I believe the driver station software allows you to plot the battery voltage even during a match.

One effective solution for the exact problem you mention where you brown out when changing direction quickly is to add a voltage ramp to drive code. If you are using the SRX (or older Jaguars), this can be configured directly - otherwise you need to add a ramp to the commands to the speed controllers. I think we targeted 48V/sec or 0-12V in 1/4 sec.