Holonomic + gyro/PID

[Jogo]

Wow you guys are all really helpful! I think two separate issues are coming up here, mostly due to my ignorance.


1) Driver-centric vs. Robot-centric: It seems that this issue is not related to the type of drive train. For example, by turning the joystick into a polar coordinate, if I push the joystick to (0.5,pi/4), then I could see using a gyro to constantly PID to the angle even without holonomic wheels. Error in this case could be caused by the gyro, which if it mounts up might require the driver to zero the gyro midway through the match.

2) Holonomic vs….well, non-holonomic: Having never tried a holonomic drivetrain, I was wondering if error could mount up naturally. For example, pushing the joystick to (0.5, pi/4) might for some reason not move the robot at precisely this amount due to environmental factors. I was wondering if teams use a gyro or other sensors to deal with this, but maybe this isn’t a significant problem.

I'd appreciate any attempts to help clarify this stuff for me. Thanks

[Ether]

Originally Posted by Jogo

2) Holonomic vs….well, non-holonomic: Having never tried a holonomic drivetrain, I was wondering if error could mount up naturally. For example, pushing the joystick to (0.5, pi/4) might for some reason not move the robot at precisely this amount due to environmental factors. I was wondering if teams use a gyro or other sensors to deal with this, but maybe this isn’t a significant problem.

This isn't a holonomic vs non-holonomic question. You could ask the same question (or a similar question) about a simple tank drive: "If I push both joysticks forward by the same amount, will the robot go precisely straight ahead?". The answer is no, and it doesn't matter because the driver adjusts (within reason) the joystick position(s) to get the response he seeks.

The only reason holonomic is different is because it has three degrees of freedom, and it's annoying for the driver if, for example, he's got a Halo-style interface and he has to continuously hold a rotation command in order to keep the robot from rotating while he's busy working the fwd/rev and strafe joystick. That's when gyro feedback or a "calibrate" button on the joystick is nice to have.

[Jogo]

Alright, I'm starting to understand. In the case of holonomic, there is usually joystick 1 (fow/rev and strafe), and joystick 2 (rotation). Would it be advisable to use a P/PID function that controls the rate of rotation of the robot? For example, if joystick 2 is at (0,0) but the gyro senses 5deg/sec, make some corrections. No reason to use P/ID on fow/rev and strafe?

[Ether]

Originally Posted by Jogo

Alright, I'm starting to understand. In the case of holonomic, there is usually joystick 1 (fow/rev and strafe), and joystick 2 (rotation).

That is one of four popular ways to do it. It's called Halo-style. See this link for 2 other ways. A fourth way is to use a 3-axis joystick: X, Y, and Z (twist).

Would it be advisable to use a P/PID function that controls the rate of rotation of the robot? For example, if joystick 2 is at (0,0) but the gyro senses 5deg/sec, make some corrections.

If your drivetrain is well-designed and balanced, and your wheels are carefully aligned and the mec rollers spin freely, and you use PID to control the 4 wheel speeds, it shouldn't be necessary.

But you can if you want. Here's one way.

No reason to use P/ID on fow/rev and strafe?

Right. Besides, how are you going to sense fwd/rev and strafe speeds for the PID process variable input? With a couple of idler wheels?

[Jogo]

Cool, even if it isn't necessary during driver control, it would likely be for autonomous mode.

Thank you so much!