SPARK MAX "Output Current" abnormally high

[0x54796C6572]

Hey everyone, so our team just got some new NEOs and SPARKs for the first time and I was playing around with them looking at the sensor readings. However, when I tried to plot “Output Current” in the Run tab, I would get a reading of about 72A constantly no matter what percentage output or load my motor is running at. Sometimes there would also be a sudden jump to a lower reading, but mostly it just stays constant at ~72A. Now obviously there’s no way the motor is actually pulling 72A, so what is the “Output Current” actually measuring? Is this number normal?

[OroArmor]

We also had this happen once, but it was about 85 amps.

[bsimmons]

We got 125A, made me freak out, the realise that there was no way it was correct.

[0x54796C6572]

It seems to be pretty consistent for us. The current measured about 72A every time I tried plotting it, and it also seems to be the same across multiple MCs (although I’m not sure if the other one I tested on was different). I’ve never gotten a current measurement that makes sense. Was it also consistent for your teams, or was it just an occasional anomaly?

[dyanoshak]

That does sound high. Do you get the same current value when reading that number through code rather than on the run tab? Are you plotting any other signals besides Output Current?

[0x54796C6572]

I have not tried reading the output current value through code yet, but I’ll try that once we get the electrical set up. I think I also plotted velocity and sometimes bus voltage and motor temperature along with output current at the same time.

[0x54796C6572]

I just tried measuring it again today and the problem seemed to have magically gone away. However, I have some other problems:

Here’s what got when plotting the output current today:

This seems to make much more sense, but I’m not sure if it’s accurate, as I believed the motor would pull much more current when running at full speed.

---

Also, it seems like reading the output current value in code results in values that make much more sense, but they also have some big fluctuations:

The motor was running in open loop mode at 100% output, with no load. I don’t know much about motors, but I’m pretty sure that it did not pull nearly 7.5 amps and drop back down to 0 instantly. those numbers are also wildly different from the ones measured from the same motor shown above.

Finally, while testing the drivetrain code today, I found that the motors would suddenly completely stop. The motor is in coast mode and has a 1 second ramping rate, so I was really surprised to see this happen. It also seems to be completely random. Any idea what’s wrong?

[Will_Toth]

Any idea what’s wrong?

Are there any faults reported? Can you output some telemetry from the device? Can you check that you code is commanding output correctly? Is the stopping behavior different compared to if you disable the robot?

[0x54796C6572]

Here’s what it looks like when the stopping happens:

The first drop in velocity is when it suddenly stopped, versus the second drop, which was when the robot was disabled (the motor is in coast mode). As you can see there’s a very big difference.

This graph shows more information:

Each one of those sudden drops in velocity is the motor suddenly stopping completely, and then accelerating again (since the joystick was held down). And weirdly enough no faults or sticky faults were reported this entire time. The “Applied Output”, which seems to be the percentage output given to the motor (even though it’s measured in volts???), dropped to 0 immediately. In comparison, here’s what it looks like normally:

.
Here’s the code that was used to do this:

double y = -controller.getRawAxis(Y_AXIS);

if(y > 0.9) {
	drivetrain.setMotors(0, 1);
}
else {
	drivetrain.setMotors(0, 0);
}

As you can see, even though the code just sets it to either 1 or 0, the ramping and coast mode still make the velocity change relatively smooth. In contrast, that weird bump in the middle is from the motor trying to accelerate, but suddenly stopping.

[0x54796C6572]

Also, the Output Current went back to 72A again, and would sometimes randomly drop to 24A and stop there. No idea what it’s actually even measuring.

[0x54796C6572]

Nevermind, it seems like the problems have magically gone away. it might be just a comms issue after all.