Hello, when my team runs our System identification for our drivetrain the dynamic tests don’t really follow what the example video on the docs shows. Our drivetrain setup is 4 spark maxes connected through CAN to 4 NEO motors with a NavX gyro. The back two spark maxes have REV through bore encoders connected to their data ports and the encoders connected to our gearbox’s output shaft.
During the quasistatic tests, it follows the example video, however when we try the dynamic tests the robot goes a bit jittery where the motors sound like they’re going back and forth. A different time we did the dynamic tests the robot would start turning to the left. Sadly I don’t have a video and don’t have the outputs of our tests to show and won’t be able to for a bit, but I can show what our config looks like.
If the turning to the left is only gradual that is supposed to happen, otherwise I am un aware of a solution to this issue, only thing I would know is make sure your wpilib stuff is up to date. Also though, if you are using Spark Maxes and neo’s, you can select built in for the encoder.
I have no idea what your issue is, it is the weirdest SysID issue I have ever heard of. The built in encoder really would only change your results that you get back. The only other things I could think of would be physical issues like wiring or maybe you have some motor inverted incorrectly. If you want to calculate these constants there are other ways to do it.
You can slowly increase the voltage until the robot moves for kS, and you can set a voltage for kV and measure the speed. The. You take the (voltage applied - kS)/speed. Not sure about kA though. kA is the voltage required to accelerate at a rate of 1 meter per second squared. I would guess that if you moved at a constant voltage and then upped it one volt you could do (newSpeed - oldSpeed)/timeToFinishAccerating to get the acceleration, then kA would be equal to 1/acceleration.
If you had perfect measurements and no noise, yes. In practice, acceleration is extremely hard to measure due to vibrations, discretization, and timing constraints; and you either need to collect enough data for a regression (what SysId does) or else estimate kA theoretically.
Good idea from @vargoose84 try lowering the voltage for the dynamic test to see if that works. If it does that means your motors are drawing to much current and you need to change the gearing.
