Using PID with Talon SRX and Mag Encoder

[Trinitrotoluene]

Hi all,

We are still trying to control an arm with Talon SRXs and CTRE's magnetic encoders. We would like to be able to move the y-axis on a joystick, have the arm move up to a set position (currently in rotations because I can't find a way to change it), and hold there until the joystick is moved again. I have a bunch of questions concerning how to go about this. I have read both Talon SRX manuals several times (Software Ref and Motion Profile).

1. Right now, I am using the Talon SRX configured with Percent VBus in Begin. In TeleOp, I have logic that causes the arm to move up to a certain point and then stop. However, when the joystick is moved, it moves rapidly and doesn't hold it's position, although the brake is enabled in the RoboRIO web dashboard.

I feel like I am going about this wrong, and that I should have the Talon set to Position in Begin, but whenever I do this I can't get a response.

2. There is also a block for the Talon SRX called "Set PID". I've been watching a lot of videos and reading a lot of posts about this, but I still don't understand the first thing about PID. It can be configured in the Web Dashboard and through the block, but how would I activate it with the joystick if I used the Web Dashboard? Also, I think it would control the movement of the arm, but are there units to the values of P, I, and D so that I can figure out how to set them?

From watching a video, I believe P is the desired position, and I and D adjust around the position to get closer to the desired position. If I wired the joystick's y-axis to the P value and somehow converted the joystick value to rotations or degrees, would this work? If so, how would I set I and D?


As you can tell, I am really confused trying to figure out how to implement this. Any examples or explanations would be greatly appreciated. Thank you.