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Unread 06-04-2011, 10:07
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Al Skierkiewicz Al Skierkiewicz is offline
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Re: Robot Power Issues

Nemo,
It is possible that some of the rollers in the drive are sticking or dragging which gives the same effect. Did you ever try to crab (left or right) and also reset? I have had more than one team report their hardware on their mecanum wheels suddenly came loose.
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Unread 06-04-2011, 10:17
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Jared Russell Jared Russell is offline
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Re: Robot Power Issues

How many motors (and what kind) are on your bot? In Florida, we were running 4 CIMs, 1 FP, 3 RS-775s (that developed case shorts, providing low resistance paths between the battery leads), and the compressor, and at times we browned out the cRIO when everything was running at/near stall at once. The heavy current draw is even worse when you have poor or loose connections in the current path and/or BaneBots motor case shorts (adding to the resistance and therefore voltage drop).

Perhaps try watching your battery voltage if/when you can reproduce the problem. Plotting the battery voltage (with LabView or a Dashboard program) is even better. If you see it dropping (even momentarily) south of 5 volts, you risk causing a cRIO power cycle (the PD board requires ~4.5 volts to maintain nominal voltage to the cRIO).
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Unread 06-04-2011, 10:20
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Re: Robot Power Issues

A few other things to check:
- Make sure nothing inadvertently shorted to your robot frame. You said this started happening after a hard hit... it's possible that hit knocked something loose and short to the frame. After that, all it takes is one loose thing to cause a second short to the frame and momentarily cause a huge power drop.

- Check your main circuit breaker. There was a bad batch of them last year, and some may still be floating around. Turn on the robot and, while watching the LED's on the power distribution board, tap the red button on top of the main breaker. Not hard enough to turn it off, but don't go very soft either. If the lights on the PDB flicker, you probably have a bad main breaker and should try replacing it.

- Finally, try driving it around and recreating the issue during practice. Have someone watch the battery voltage readout on the driver station to see if it suddenly drops while performing any specific maneuvers. As Al has already said... issues in the drive train (loose chains, problems with the mecanum rollers, etc) can cause momentary binding that leads to a huge amount of stall current going to the CIM's, momentarily dropping your voltage below what's needed to keep the cRio powered.
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