Jaguar Speed Control Only Reaches 50% of Setpoint

[techhelpbb]

Originally Posted by AustinSchuh

I'm going to take the position that if someone is using just a P controller to try to get the robot to drive at a velocity, they are doing it wrong. They should first start with the I term, and leave the rest of them 0. Would you every try just using the D term in a PID loop when trying to go to position? You'd say that the person was doing it wrong if they did that.

Not really stating that the P loop alone should drive the robot. Merely looking for an optimal tuning procedure based on the Jaguar's implementation of PID.

If you read the available information, without wandering into this topic, I suspect you'd try tuning the P loop alone first as a student as well (I can prove that easily because that's exactly what 2 students on our team did independently after trying to work out the presented information within the limits of their math skills).

Hence the reason I seek clarification and the others seek to compare notes. I recognize you feel that this is burdensome math to some extent, but the issue is not whether or not I understand it (or believe you as you put it), it's how anyone expects teams to tune these PID loops with the available information unless they have someone much more familiar with the subject to refer to. To put it bluntly, show me where the section with suggestions on tuning the parameters for the Jaguar PID loop is in their documentation.

I'll confirm with the students tonight, but I'm fairly sure they didn't use a P gain higher than 7 before instability occurred.
I'm pretty sure that we didn't have 50% error at that point. I could be wrong, but we'll surely find out.

UPDATED: They were never able to exceed 6 with one or 6.3 with another for the P gain before instability. Around those values the error was 10%-15% for us.

Of course the point of this discussion about the Jaguars and how they work was to wring out issues like this:

Originally Posted by AustinSchuh

Assuming velocity is measured in meters/sec, and the jaguar takes volts as it's input, which is probably not the case for the supplied control loop.

Obviously the discussion itself hinges on finer details like you wrote above. As tuning into the marginal is effected by the actual feedback and the inconsistencies that it may create.