[FTC]: External Battery Not Connected??? HELP?

[FTC6389]

Just a quick follow-up for future teams that may have this problem...

It turned out to be a bad MC (motor controller). We figured this out by switching the around the connection order between the MCs and the NXT.

Our original config had 3 MCs and 1 SC daisy-chained together and connected to NXT port S1. Remember that the NXT only polls the first MC on port S1 to determine the state of the external battery. So, if that MC reports "No External Battery", back to RobotC, nothing will work, and no commands will get to your motors, even though the red MC light is on (visually telling you that there is actually power getting to that MC. This is the really frustrating part!)

While trying to diagnose the issue, we disconnected the first MC in the chain and then connected it to NXT port S2 by itself. We then hooked the remaining chain of 2 MCs and 1 SC back up to NXT port S1 and ran our Teleop program again in the RobotC debugger. Using the "External Controllers" debug window, we were able to watch as the voltage of the MC on S2 went from 12.8V to "Not Avail" while the chain of controllers on S1 continued to work and report appropriate voltage. Again, the red led on that MC was on all the time, even when it was reporting that it had no power.

Bottom line... When you have an issue in a complex system that seems to make no sense, breaking the problem down into the most atomic pieces you can, and scrutinizing each piece individually can help identify the issue.

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FTC6389