Sidecar Brownout causing motors to move

[Thad House]

We were testing our drive today with a dead battery accidentally, and whenever we would reverse the drive we could see the sidecar was browning out. We know not to do this, but when it happened all the Talons would turn on backwards for a split second. It this the expected behavior for a sidecar brownout, or do we have a bad sidecar?

[Al Skierkiewicz]

Thad,
If the DSC was browning out so was everything else on the robot. All bets are off when that occurs. Most often the DSC power supplies start to fail at about 5.5 volts, the PD power fails at about 4.5 volts. If there is a sudden surges, a lot of noise is generated in all of the control systems. I have not heard of a brownout fault with the Talons, but you might want to check with Mike at Cross The Road.

[RufflesRidge]

Originally Posted by sst.thad

We know not to do this, but when it happened all the Talons would turn on backwards for a split second. It this the expected behavior for a sidecar brownout, or do we have a bad sidecar?

Yes, this seems like an expected behavior:

The robot is enabled and you're driving it around. This means that the cRIO is sending PWM signals to the motor controllers via the Digital Sidecar with nominal high pulse width of 1.5ms (neutral) +/- .5ms (forward and reverse respectively). So you're in the middle of sending one of these pulses, and the Digital Sidecar browns out and stops sending the high signal so you have a pulse that is much shorter than what the controller was trying to send.

Some tests we've done with some of our Talons and a pulse-width generator show that they will respond to a signal much shorter than 1.0 ms with full reverse. So your truncated signal is interpreted as full reverse. The Talon then looks for another pulse for a little bit, but doesn't get one so it disables the output.

[Thad House]

Originally Posted by RufflesRidge

Yes, this seems like an expected behavior:

The robot is enabled and you're driving it around. This means that the cRIO is sending PWM signals to the motor controllers via the Digital Sidecar with nominal high pulse width of 1.5ms (neutral) +/- .5ms (forward and reverse respectively). So you're in the middle of sending one of these pulses, and the Digital Sidecar browns out and stops sending the high signal so you have a pulse that is much shorter than what the controller was trying to send.

Some tests we've done with some of our Talons and a pulse-width generator show that they will respond to a signal much shorter than 1.0 ms with full reverse. So your truncated signal is interpreted as full reverse. The Talon then looks for another pulse for a little bit, but doesn't get one so it disables the output.

That was exactly our thought too. We just wanted to double check and see if there was something else wrong with something else on the control system. We know to not brown out, and will make sure to have a charged battery to control it.