no voltage across PWM pins on roboRIO

[Fritz_Haber]

After testing on bag day, we went over the moat and attempted to move an arm with an encoder when it became apparent the encoder had stopped functioning. After debugging the problem (same encoder, alternate RIO, etc), we tested the voltage across the PWM pins on the roboRIO and found 0V between power and ground (the two outside pins) while the RIO was plugged in.

First of all, is this a problem internal to the RIO? Secondly, could someone point me towards how the RIO handles physical shock? on the current robot, it is mounted on polycarbonate which is mounted rigidly to the frame, so there is no vibrational damping. Such a system could be implemented, but I am curious if other teams have also encountered problems with their RIOs and vibration given the rough nature of the game.

[The Lucas]

Most likely the shock has caused some metal shavings to short power pins in your rRIO. Is the power LED red?
https://wpilib.screenstepslive.com/s...uick-reference
It is a common problem. I sometimes don't even notice it because I use the VRM to power all sensors.

[Ether]

Originally Posted by Fritz_Haber

...the encoder had stopped functioning... we tested the voltage across the PWM pins on the roboRIO and found 0V between power and ground (the two outside pins)

1) The two outside pins of PWM are signal and ground, not power and ground.

2) Encoder plugs into DIO, not PWM.

[Fritz_Haber]

Thanks Ether, I'll be sure to double check the measurement tomorrow.
Lukas, I believe the power LED was on (I think it was red) and we did find some metal shavings inside it. A simple short doesn't (usually) result in permanent damage right?

When we were testing an alternate encoder, we ran a separate motor from a separate power supply while plugging the encoder wires into the roboRIO on the robot (running on a different power supply). Someone mentioned a potential issue with the two being grounded differently (my understanding is if everything is run off the same power supply, the grounded wire from the encoder connected to the roboRIO eventually connects back with the grounded wire from the motor and goes to the battery ground). Is this two power supply setup an issue?

[matthewdenny]

We had a similar problem trying to run a servo. (no voltage between power and ground). We opened it up, but couldn't locate the problem. We called NI and they sent us a new RoboRio via Andymark in ~ 2 days. Sent the old one back.

[Greg McKaskle]

If there is an issue with the voltage rails providing power to the robot, the roboRIO should be reporting it via the power LED and on the DS power tab. Look of the short within the robot wiring, look at the base of the roboRIO pins, and if it persists when nothing is plugged in, the short may be within the case.

The power tab should go red whenever something interesting related to power has happened. Clicking on it will tell you some info about which type of power issue you have.

Since we are most likely talking about some debris inside of the roboRIO causing a short. Let me throw in a friendly reminder not to sprinkle your electronics with metal shavings or small pieces of wire. Get in the habit of covering electronics and or using a vacuum whoever you are drilling/filing/sawing or otherwise turning large pieces of aluminum into smaller ones.

If you believe that your roboRIO may have this issue, let the mentor/coach know, or if at an event, get a CSA to assist. NI support is there for issues like this, so get in contact with them.

Greg McKaskle