Originally Posted by rich2202 (Post 1573691)

In theory, PID is great. In practice, not so much.

In this exercise, you are trying to turn a robot to a set angle. PID will increase the speed until you get there, and then oscillate back and forth trying to hit the mark. The easier way to do it is to turn at a controlled speed until you get there.

In the original code, I'm guessing that the robot is rotating too fast, and overshoots the error range (self.desired to self.desired+10) that one time in 10. The solution is to turn slower, check the angle more frequently, wider error range. Maybe when you get close, you slow down the turn.

Originally Posted by DanielHa (Post 1573655)

at certain absolute angles, if you simply add or subtract 180 (or in your case the slightly altered values), then you might get a value which is outside the range of the navX.

Originally Posted by Ether (Post 1573836)

Let S be your sensor angle reading (in degrees, can be any range, even outside the range +/-360)

Let T be your desired angle position (in degrees, can be any range, even outside the range +/-360)

the angle between them (let's call it ERR) is found by the equation:

ERR = (T-S) - 360*floor(0.5+(T-S)/360);

the above returns a value for ERR between -180 and +180 degrees,
the shortest angle path to the target. Don't believe me? Try it.

So it tells you which direction to rotate as well as how much to rotate.

To use this with a PID, use processVariable = setpoint-ERR

Originally Posted by Oblarg (Post 1573892)

This is unnecessary with the NavX and WPILib, as one can simply call AHRS pidGet() (which always ranges from -180 to 180) and ensure that the PIDController object is set to have a continuous range and not have to ever explicitly do any of the math.

Originally Posted by Ether (Post 1573894)

Yes.

I was responding to DanielHa's post, to show a simple way to compute shortest angle... which would be useful to know for situations where the library functions or the hardware don't do the math for you.

Originally Posted by Jared Russell

I would argue that PID is much more elegant in practice than in theory.

Originally Posted by Foster (Post 1573947)

Exactly! Always good to go "Umm I need to do this, looks like that library does that, oh wait it won't work in all cases".

Originally Posted by Oblarg (Post 1573956)

reinventing the wheel is not generally good coding practice and if you have a library that does what you want (in this case, you do) it is good to use it.

Originally Posted by Ether (Post 1573965)

In case you have inferred otherwise, nothing I posted in this thread should be construed as antithetical to the above.