Our robot is twitching and our coms randomly disconnects

Hi! Our robot currently uses Spark Max’s and NEO motors. Sometimes when driving, we lose the connection to the robot for a very brief amount of time (like 0.5s) and then our robot and motors start twitching. Currently, we are hypothesizing some CAN issues or ethernet cable disconnecting. Do you guys have any ideas as to why this is happening?

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Please share some driver station log files covering a period where this occurred. We need both the .dslog and .dsevents files.

Log Files.zip (294.9 KB)

This is our first time inspecting log files so we’re not sure how to upload them so I decided to zip them up and send them over. The problem occurred most clearly at about 4:46 PM. When the robots start to jitter, the Spark MAXs start to flash blue. We thought it was a CAN issue and rewired most of our robot. Then, we tried changing the current limit in our Spark MAXs. Perhaps it could be a software issue in our code but we don’t know how to figure that out (we used the example code from REV robotics). Please help us. Thank you!

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I haven’t looked at the log files yet, but wanted to key into something you stated. You mentioned the SparkMax’s started “blinking blue”. Can you provide a better description? Have you referenced the blink patterns in the documentation?

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All the Spark Maxs starts blinking light blue (“no signal” on the brushless motorrs) at random times.

We had that issue at one of our competitions, I would check the CAN JST-PH connector (the white one) going into your SPARK MAX. We found that a motor that exhibited similar issues to you guys had the green wire slightly out of the connector.

We’re looking into that right now. Thank you!

Do you get CAN errors showing in the driver station logs? That would be further evidence of a wiring fault (as mentioned by @superpenguin612). If its just the one device (and your connector is one of the newer ones that has passthrough loops), then the break is almost certainly at that connector or internal to that SparkMax. If you see multiple IDs listed in the error, then the break may or may not be at that connector.

No, we did not. The only thing we saw was “FRC: the Driver Station has lost communication with the robot” on our dashboard.

We finally caught a video of it twitching here: https://imgur.com/a/1vI7V0c. Any help in identifying the issue would be greatly appreciated.

Seeing the status light turn solid for a short bit is a bit concerning. It seems to me that the robot is disconnecting from the driver station. Is the radio mounted securely and nothing bumping against it? Same with the power to it? What is your battery voltage while this happens?

Do you have redundant power to the radio? (ie Power over internet AND the barrel connector)

Yes, our radio is mounted securely and nothing is bumping against it and the power to it. Our battery voltage dips when it happens to around 9V but not consistently.

No, there is only power over ethernet.

Looks like your radio is mounted pretty close to a brushless motor. In theory that could cause interference which would cause the packet losses described in your teammate’s post. Maybe try moving it higher up on the elevator and see if that helps

I believe the culprit is here somewhere. Your battery volts should never get that low. Even with swerves and compressor running at once, we don’t go below the 11s. Does it do it with different batteries?

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It does seem to do it with other batteries as well. We can’t seem to replicate the problem however by moving the robot around and making it go below the 11s.

Sure, I’ll try that.

Then you must have magic batteries, because getting down to ~9 is incredibly common in high-load situations. There’s a reason the roborio brownout protection mode doesnt kick in until ~7V


This seems like it might be a current spiking issue. In the driver station logs you can see which PDH port is drawing what amount of amps, the. You can see what is drawing that much and current limit that.

You also might need to look at the peak current time (i forgot the exact parameater name) but at least CTRE products (mayeb REV) have a configurable amount of time thst it will allow it to go above the ser peak current limit.