paper: Take-Back-Half Shooter Wheel Speed Control

[tr6scott]

The Bisect Ctl code shows a while loop, and you have that in the teleop code. Isn't having a while loop in the Teleop code a bad thing? Or am I missing something...

Also, does the controller need a fixed time base between iterations? It would seem that if the delta t's are not consistent, there would be issues similar to if they are not consistent in a PID loop?

We actually have the code running on our bot, but I am doing a software review, and had some questions. Not 100% FRC and Labview savvy.

[John Sabath]

Originally Posted by tr6scott

The Bisect Ctl code shows a while loop, and you have that in the teleop code. Isn't having a while loop in the Teleop code a bad thing? Or am I missing something...

They're using a while loop for glorified feedback nodes. The loop never executes more than once in a single iteration due to the True constant being wired to the Stop if True terminal.

That being said, I like the use of a while loop in this case since it makes the logic flow easier to follow.

[tr6scott]

Thanks John, I see the stop button now, not used to seeing that done. I did just take out the while loop, and rewired it all with the "normal" feed back loops, and even after the "broom of death" the code was pretty much un-readable. I see the reason for the one iteration loop, it made the code pretty.

As to the other question, what happens to the control if there isn't a consistent time between teleop iterations.

Scott.

[Hjelstrom]

Wow this is a cool algorithm. I think we'll try it next chance we get. Thanks for sharing!

[z_beeblebrox]

For shooter speed control, what are the advantages of PID or take-back-half control over bang-bang control? It seems like bang-bang control provides the shortest spin-up time, as the motor is run at full power, and, if run with a fast enough update time, accurately holds shooter speed in a small tolerance.

[Ether]

Originally Posted by z_beeblebrox

For shooter speed control, what are the advantages of PID or take-back-half control over bang-bang control? It seems like bang-bang control provides the shortest spin-up time, as the motor is run at full power, and, if run with a fast enough update time, accurately holds shooter speed in a small tolerance.

If:

1) your motor is directly connected to the shooter wheel (so there is no gearbox free play and minimal "drivetrain" friction), and

2) your wheel is reasonably balanced (so excessive vibration does not cause rapid deceleration of the wheel when power is removed), and

3) your speed feedback has good resolution and minimal phase lag (as would a properly coded counter object using the getPeriod() method), and

4) your shooter has sufficient moment of inertia (most do), and

5) you run the algorithm fast enough (20ms or faster)

... then it's hard to beat bang-bang control.

Even if some of the above criteria are not met, bang-bang can be the best method, on a case-by-case basis depending on your design.

[z_beeblebrox]

"You must spread some reputation around before giving it to Ether again"