PDP Lights

The lights on our PDP are green when the robot is enabled and driving forward or backward, but when we change the direction we drive in the color flashes red momentarily and goes back to green. I can’t find anything on this and don’t know if it is a CAN network error or not.

This seems like a CAN Error double check all CAN connections, we have had issues like this before.

@ozrien FYI

That’s a little bit of an odd flash code, but I don’t know for sure how to read it. Could be a high-power-draw thing too.

Red LED means a CAN issue (table below from users guide). Since it is momentary, that suggests the root-cause is intermittent.
I also suspect you will see red blips on other CTRE CAN devices on the bus (Talon SRX, Victor SPX, Pigeon IMU, etc.)

>> forward to backwards and backwards to forwards

This can suggest:

  • Battery voltage is dipping to a point where CAN-bus devices can’t reliably communicate (<5V)
  • There is an issue with a particular CAN-bus device causing this
  • improper termination

Next Steps

  1. The debugging steps are essentially the same as an intermittent red blips on any CTRE CAN device…
    Particularly in isolating devices to determine the root cause.

  2. A good sanity check is to measure the resistance between CANH/CANL while robot is not powered, confirm it is 60Ω

  3. Another good sanity check is to measure the resistance between CANH/CANL and robot-chassis, PDP-red, PDP-black while the robot is not powered.
    Resistance should be excessively high (>1MΩ or “OL” on your meter)

  4. Confirm that any CAN-bus stubs are within 1ft of the primary bus.

  5. Confirm termination (PDP and roboRIO) are at the CAN-bus cable ends.

  6. List the total number and types of CAN devices on your bus.

  7. Scrutinize your power paths and battery health (battery leads can’t be loose, PDP contacts can’t be lose).

Test with different batteries.

Battery beak your battery to ensure internal resistance is adequate (<0.025Ω) and charge -state is “good”.

It fixed itself so that’s good

No, it is not good.

Intermittent faults have a very annoying habit: they show up when you don’t want them to, and disappear when you are trying to root-cause them. The fact it went away on it’s own tells me that it’s likely either a low battery issue affecting CAN, or possibly an intermittent short in the CAN wiring itself. You really don’t want the latter option because if it comes back enough times, or worse, whatever is causing it migrates, you could be out a PDP.

Keep after it, observing carefully, until you’ve figured out the root cause.


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