Dynamic tests in sysid causing robot to “stutter”

We have a problem with the dynamic test of sysid. When we run the test the robot goes back and forth really fast. I have attached a video below. If you slow the video down you can see the spark max is switching from green to cyan really fast for some reason. However the quasiatic tests work perfectly displaying the right encoder readings when run. What is the problem?

I don’t know how helpful this will be, but my team’s robot did the same thing, and we just kinda ignored it

Did that not end up messing up the pid values it spit out? For our robot it give us a negative kA value which is not supposed to happen. Also the robot doesn’t stutter like this in the video in the documentation for sysid.

Oops never mind. I just checked the documentation it said the dynamic test is supposed to apply constant step voltage. I also rewatched the video and I could hear the stuttering so you are right. Sorry about that.

did you check the motors to see if they have any chipped gears or faulty wiring?

It’s hard to tell from the video, but my first guess is that your robot is browning out. Does the same issue happen if you do a dynamic test using a lower voltage? e.g. 4V instead of 12V.

If you use the data as-is you’ll probably get a bad kA value - try comparing against recalc’s predicted kA. Since kA isn’t usually all that important, you can probably get away with just using the recalc estimate if you can’t get the test working.

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Yes it was browning out if I remember correctly. I don’t have access to the robot right now so I can’t test by limiting the voltage. What could be the reason this happened?

Yes everything was wired correctly and the gears were ok.

If it’s browning out, this would most likely be caused by using a non-charged battery.

To put it briefly, your motors draw a lot of current when they’re at low speeds and you apply a large voltage. This current draw causes your battery voltage to drop, which causes the rio to enter brownout protection mode by shutting off the motor outputs so your rio itself doesn’t lose power and shut down. If you apply less voltage, the motors will draw less current and so your battery voltage will drop less. This is part of why current limits are important to implement on your robot.

For a more detailed explanation, look here:

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