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Unread 14-01-2014, 04:20
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mikets mikets is offline
Software Engineer
FRC #0492 (Titan Robotics)
Team Role: Mentor
 
Join Date: Jan 2010
Rookie Year: 2008
Location: Bellevue, WA
Posts: 675
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Re: [FTC]: Tetrix motor controller weirdness with 4 motors

Our team has very similar problems. This actually started last year where the motor controllers would freeze when the robot ran into things hard and we would be dead in the water until we power cycled the main battery. We tried everything from swapping motor controllers to tracing through wiring, swapping and bypassing ports. Nothing worked then the season ended. Then this year with a new game and new robot design (but reusing old controllers), we started okay but then the problem started to appear again. Eventually, we swapped the NXT brick with my personal brick and the problem has disappeared so far. But not knowing why and the real root cause, it may be a time bomb. We took apart one of the Tetrix controllers and ohm check the two RJ12-like connectors and found that 5 out of 6 pins are tied from one port to the other. My understanding is that the port contains an analog pin. So the 1 pin that's not tied to the adjacent port must be the analog pin. But this means the I2C bus is a passive pass-through. If that's the case, the theory on one controller froze causing all the down stream controllers to malfunction is now questionable. Don't know if it's related but our robot suffered serious electro-static discharge issue this season. Every time there is a discharge, our brick would hang causing us to lose half of our matches. That was a terrible day apparently because the weather was too good and too dry. It might explain why when we swapped the brick to use my personal brick, our motor controller problem also went away (at least for now). My personal brick was never used in competition so it never suffered any electro-static discharge as the team bricks have suffered for so many years. I would really like to get to the bottom of this issue so I don't have to worry about the time bomb blowing up on us (especially during competition).
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