NEO/SparkMax: Not functioning above a certain voltage output?

We have a bizarre problem with our SparkMax and NEO combination on our arm that just manifested between routine arm tests.

Whenever the output voltage to our NEO is set above 4.5 to 4.6 volts (+ or -) either from robot code or the REV GUI, the motor begins to behave as though it’s passing a current limit-- the REV Hardware Client shows us having this fault. However, even when having no current limit applied or using 80 amps, this manifests even while all data we have indicate no more than 4.5 amps of draw. We’re not browning out the SparkMax either.

The motor makes a loud whine as it stops moving and quickly turns on and off, and the status LED blinks rapidly between off and either red or green (depending on direction).

The odd thing is that this seems to depend based on load upon the motor, as for threshold voltage values the whole thing triggers when the arm reaches closer to horizontal, (highest load due to gravity).

This thing has persisted through multiple SparkMaxes. The motor works completely fine if you remove load from it. We’ve even popped open one of the SparkMaxes to make sure nothing has melted, no dice.

Some things that might be pertinent:

  • Motor lifting a 1.9 kg arm (~75 cm to COM)
  • NEO 1.1
  • CIM Sport w/ 100:1 reduction + 2:1 sprocket reduction between output and drive
  • Motor not heating up at all

Looking for any help we can get, thanks (we’re tearing our hair out).

It sounds like a current limit to me. 4.5V at the stated 406W sounds right for a current limit. Check that there isn’t excess resistance in the mechanism itself. It stalling at horizontal is what you would expect to be worst case.

One important thing to note is we were able to run just fine at scrimmage and week one. This has only been an issue today. As far as we could tell, there were no current limits or other obvious causes for the issue. The only thing changed hardware-wise was switching from the original Neo to a Neo V1.1 and swapping out the gearbox for a new one.

That would indicate to me that it is indeed something wrong past the motor, either in the gearbox or arm pivot. What gearbox are you using?

We are using a 100:1 CIM Sport gearbox. We had issues with our old gearbox locking up, and swapped it to a new one that has been tested (both manually and with controls) and verified to not be the issue.
After swapping motor controllers, we were able to successfully operate the arm without issue for a limited amount of time. The problem then returned

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Was it tested post stall issue, or just prior to competing?

The gearbox? It was put on within the past few days and tested before the issue and after.

We were experiencing extremely similar issues with our arm (powered by a NEO and Spark MAX) after stalling it for a significant amount of time at essentially full power (45 seconds +).

We finally tried swapping in a new spark and motor, and the issues vanished. We suspect that we damaged the spark or NEO (not sure which or both specifically at this time) with the excessive current draw experienced during the stall.

This was my next thought. Kinda dumb troubleshooting step could be swapping the neo for a CIM and try to get it to burn out.

Okay, we have been looking at swapping out the Neo, but have been trying to avoid that. We will probably end up doing that next week to see if it fixes the problem.

Although the conversation had moved on from here, it should be noted that both the PDH and SparkMAX report no more than 4.5 A of current.

From my limited understanding of motors, I think this would also indicate a motor issue.

It’s definitely not ideal (we held out on swapping ours too), but in hindsight I wish we’d have tried it sooner. We spent several hours at our last event and at our last couple meetings diagnosing things and trying to find a “cheaper” issue causing the symptoms.

If you have a spare motor and/or spark, I’d say it’s worth trying to swap them and see whether that solves things for you. If it doesn’t, just swap back and continue trying to diagnose things.

Yeah, we do have enough spares to swap. We thought about doing that but didn’t as the motor started working immediately after swapping the motor controllers (though it started experiencing the issue again not long after). In hindsight, we probably should have swapped the motor today rather than spending 5 hours debugging.

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To give an update, swapping in one of our old Neos eliminated the problem. However, when we later attempted to use a different Neo V1.1 than the one we initially experienced the issue with, the same problem began occurring after about 15 minutes. For right now, we plan to avoid running Neo V1.1 on our arm.

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