Shooter Problem

[Ian Curtis]

Originally Posted by DonRotolo

The Plexiglas arc may be too slippery, and the frisbee is slipping instead of rolling along. You may want to add something soft and squishy there, like foam tape.

Having played with a similar setup this is almost certainly the problem. Gaffer's tape on the arc worked really well, if you don't have any of that masking tape would probably work about as well. We're going to try hockey tape tomorrow.

[MrForbes]

We have plans to try several of the tricks mentioned here, and we'll try to report back with our findings.

[roystur44]

Check and make sure the wheel is tighten to the axle and is not slipping

[Jeffy]

We found tread material to give us the most difference in performance. We use wedgetop wheel tread and it works well on a 6 inch wheel.

[DonRotolo]

Originally Posted by ThePlagueDoctor

The frisbee rolls and moves in the shooter just fine, its just that it doesn't launch that far, barely at all...

OK, let's say it is slipping 90% - you would never be able to see this with your 'bare eyes'.

As Ian Curtis mentioned, try some tape on the plexi. Then come back and tell me it didn't work, But not before you try it, all right?

[MrForbes]

Originally Posted by Jeffy

We found tread material to give us the most difference in performance. We use wedgetop wheel tread and it works well on a 6 inch wheel.

This is what we're planning to try tomorrow. And we'll set it up so we can play with the speeds, by using chain drive and computer speed control, eventually with a PID loop of some type.

[ThePlagueDoctor]

Originally Posted by Ether

That gives you a lot of headroom to do closed-loop speed control. A bang-bang controller probably will work very well.

Also, interested in your answer to Aroki's questions about the gearing and the wheel.

We are using a 8 inch high grip wheel directly driven with a cim

[Ether]

Originally Posted by MrForbes

This is what we're planning to try tomorrow. And we'll set it up so we can play with the speeds, by using chain drive and computer speed control, eventually with a PID loop of some type.

Try P-only and crank the gain up to the sky*. If you've got enough inertia in the wheel, and you run the loop at 10ms, that's all the tuning you should need.


* this will mimic a bang-bang controller.

[Dinoyan]

We know how we're going to shoot but how we're going to put the frisbees in to the robot or how will the robot going to pick it up????.

[Woolly]

Originally Posted by Ether

Try P-only and crank the gain up to the sky*. If you've got enough inertia in the wheel, and you run the loop at 10ms, that's all the tuning you should need.


* this will mimic a bang-bang controller.

Yeah, I'd say that you might want to go with a bang-bang controller.

If you get flack from your mechanical/fabricators for "slamming" the motor, do what I did, add a linear cushion within ~3% of your target speed.
Ex. For a shooter wheel capable of 10,000RPM when you're over 300 RPM lower than your setpoint, you go 100% power, when you're 150 RPM Lower, 75%, Dead on 50%, 150RPM Higher 25%, 300RPM Higher 0%.

This will mimic the PID you're trying to use, and unless you really know what you're doing when PID tuning, will be half the headache.

[Ether]

Originally Posted by Woolly

If you get flack from your mechanical/fabricators for "slamming" the motor...

Seriously? Are you saying there was some visible or audible manifestation?

If so, check the following and fix if necessary:

- make sure the motor controller jumper is in the "coast" position (not "brake").

- make sure you are running the control loop fast enough (10 ms is good)

- make sure your sensor is capable of giving an up-to-date speed reading faster than your control loop iteration rate

[Woolly]

Originally Posted by Ether

Seriously? Are you saying there was some visible or audible manifestation?

If so, check the following and fix if necessary:

- make sure the motor controller jumper is in the "coast" position (not "brake").

- make sure you are running the control loop fast enough (10 ms is good)

- make sure your sensor is capable of giving an up-to-date speed reading faster than your control loop iteration rate

I didn't know what I know now when I made that control loop last year, and I just dropped it in autonomous and teleop. Obviously a case of it not running fast enough. Still, even our poor bang-bang controller was better than a PID for this application.