Hello, recently we have been experiencing 12V across our robot frame. I test this by putting the positive lead of a multimeter onto the positive 4AWG of our main breaker and then the negative lead onto the frame. We unplugged everything and from the PDP and the issue went away but as soon as we plug in any motor controller or CAN bus it comes back. It doesn’t matter what motor controller we plug in the issue comes back. Any help would be great. I’m thinking it may be a dumb mistake in my testing.
It doesn’t matter which motor you plug back in? It always comes back?
I don’t know if there is a proper way but I usually test frame Isolation from the negative 4AWG lead of the main power.
have you tried disconnecting the RIO and VRM power cables as well?
The next thing to also try is putting the multimeter to the frame and to the negative lead of each motor power wire.
Hopefully only 1 will fail and you can keep going from there
Also: You’re checking voltage, yes? The inspection checklist calls for resistance if I’m not mistaken.
I usually test for connection. (The one that beeps when there is a connection, idk the exact name of the mode) But I’ll be honest I have no idea if thats the same as what your mentioning
It doesn’t matter which controller. As soon as we connect a controller to any slot it goes back to 12v. Sometimes it goes to 7v. We disconnected the vrm, pcm, and Rio and nothing has changed.
You’re testing for continuity, which checks for zero (or very little) resistance, indicating a short. Checking voltage will be similarly effective though, you should measure 0v across the frame and ground, not 12. Neither the positive or negative terminal of the battery should have continuity to the chassis.
Although the inspection calls for resistance wouldn’t 12v on the frame cause issues as well?
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I dont think it will change anything, but what controllers/motors are you using?
Edit: Oh and any custom circuits?
We measure 7-12v when we connect the positive lead to the main breaker and the negative lead to the frame
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Talon SRX, victor, SPX, spark max’s and falcons. No custom circuits.
Isolate one item at a time back to the PDP. Slowly remove each device on the line - starting with the roboRIO, then each motor controller, etc. Check for resistance each time you remove a device. If during this process you find the problem, then great!
If you still haven’t found it, or need help looking:
pro-tip: Signal sized wire can easily get pinched in a mechanism or by a staple etc. Remove these wires also.
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Can you try measuring continuity/resistance? You might be able to measure voltage even with sufficient (per resistance) isolation since your meter might be 100k or 1M ohm input impedance.
Think about it. You’re measuring 12V from +12V to frame (should be isolated).
Given that you’re looking for HIGH RESISTANCE (or should be), I’d expect a relatively high voltage differential given high resistance.
R42. All wiring and electrical devices, including all Control System COMPONENTS, shall be electrically isolated from the ROBOT frame. The ROBOT frame must not be used to carry electrical current.
R42 is checked by observing a >3kΩ resistance between either the (+) or (-) post within the APP connector that is attached to the PDP and any point on the ROBOT.
All legal motor controllers with metal cases are electrically isolated. They may be mounted directly to ROBOT frame COMPONENTS.
Note that some cameras, decorative lights and sensors (e.g. some encoders, some IR sensors, etc.) have grounded enclosures or are manufactured with conductive plastics. These devices must be electrically isolated from the ROBOT frame to ensure compliance with R42.
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Do you disconnect the CAN from each controller while doing this? or is it all still connected?
If its all still connected I suspect thats where the problem is
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We finally disconnected the CAN BUS that was in the pcm (the pcm wasn’t even powered) and the 7v went away. How can that be happening if the pcm is not plugged into the pdp?
What else is connected to the PCM?
How could I test this?
Might help to first understand the difference between “resistance” and “voltage”. And how to test for each, using a multimeter.
CAN bus is the only thing besides solenoids. The power is not even connected to the pcm.
Did you carefully inspect the CAN bus wire to make sure it’s not pinched against the chassis anywhere?