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Unread 22-04-2012, 16:49
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Re: paper: Shooter Wheel Speed Control

We've settled on PID because we simply can't get the bang-bang method to give us better results. The real issue that I think I've hit is mechanical - we're at the limits of what our system can provide. No matter how we play with gains, filtering, etc, we're struggling to get the shooter more than +/- 40 to 60 rpm (actual RPM, not filtered much at all other than to remove big spikes that are obvious errors).

Filtering the speed before our 'enable shooting' vi really doesn't help shooter run any more consistently - it just makes it easier for us to check the limits.

I did put a 4 sample moving average in to filter the pid input. That helped with some of the oscillation. We also turned down our proportional gain (we wrote a velocity PID, we're not using the position PID) to help some of the oscillation. The shooter still spins up in around 2 seconds, but that helped the oscillation as well.

I had hoped to manage a major improvement before nationals. We've improved our velocity control probably 50%, but other folks are reporting numbers that are still close to 100% better than ours. That means that in real time ball shooting, we're seeing something like +/- 1 foot in height when hitting the backboard.
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Unread 22-04-2012, 17:10
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Re: paper: Shooter Wheel Speed Control

Hey, I didn't read the whole thread but just wanted to mention that this will not work with a Spike. I haven't tested, but a while ago I read into how the Spike works and it cannot coast, it either powers the motor or breaks.
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Unread 22-04-2012, 17:16
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Re: paper: Shooter Wheel Speed Control

Quote:
Originally Posted by NeatNit View Post
Hey, I didn't read the whole thread but just wanted to mention that this will not work with a Spike. I haven't tested, but a while ago I read into how the Spike works and it cannot coast, it either powers the motor or breaks.
Not true for this application, since motor is being driven in one direction only.

Connect one lead of the motor to the PDB(-), and run the other lead through one relay in the Spike to the PDB(+).

anyone: Is this FRC legal?


See ensuing posts. Doh!



Last edited by Ether : 22-04-2012 at 18:11.
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Unread 22-04-2012, 17:29
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Re: paper: Shooter Wheel Speed Control

Quote:
Originally Posted by Ether View Post
Not true for this application, since motor is being driven in one direction only.

Connect one lead of the motor to the PDB(-), and run the other lead through one relay in the Spike to the PDB(+).

anyone: Is this FRC legal?

Either way, the SPIKE can connect that side of the motor to either + or -, so wouldn't it still break when both sides are connected to -? (regardless of one passing through a SPIKE and whatnot)

I could of course be very wrong
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Unread 22-04-2012, 18:06
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Re: paper: Shooter Wheel Speed Control

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Originally Posted by NeatNit View Post
Either way, the SPIKE can connect that side of the motor to either + or -, so wouldn't it still break when both sides are connected to -? (regardless of one passing through a SPIKE and whatnot)

I could of course be very wrong
No, you're right.
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Unread 22-04-2012, 17:32
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Re: paper: Shooter Wheel Speed Control

Quote:
Originally Posted by Ether View Post
Not true for this application, since motor is being driven in one direction only.

Connect one lead of the motor to the PDB(-), and run the other lead through one relay in the Spike to the PDB(+).

anyone: Is this FRC legal?


It wouldn't be FRC legal.

Also, because a Spike is a mechanical relay, don't they have a limit as to how quickly they can switch to ON/OFF?
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Unread 22-04-2012, 18:02
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Re: paper: Shooter Wheel Speed Control

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Originally Posted by nighterfighter View Post
It wouldn't be FRC legal.
When you make such a statement, you should reference the rule you have in mind.


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Unread 22-04-2012, 18:04
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Re: paper: Shooter Wheel Speed Control

Quote:
Originally Posted by nighterfighter View Post
Spike is a mechanical relay
I'm not saying you're wrong, but what is your source for this information?


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Unread 22-04-2012, 18:10
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Re: paper: Shooter Wheel Speed Control

I think the rule violation would either be:

Quote:
[R47]

Custom circuits shall not directly alter the power pathways between the battery, PD Board, speed controllers, relays, motors, or other elements of the Robot control system (including the power pathways to other sensors or circuits). Custom high impedance voltage monitoring or low impedance current monitoring circuitry connected to the Robot’s electrical system is acceptable, if the effect on the Robot outputs is inconsequential.
Or, more likely this one:

Quote:
[R50]

All electrical loads (motors, actuators, compressors, electric solenoids) must be supplied by an approved power regulating device (speed controller, relay module, or Digital Sidecar PWM port) that is controlled by the cRIO on the Robot.

Each CIM motor and Fisher-Price motor must be connected to one and only one approved speed controller. These motors must not be connected to relay modules.
Servos must be directly connected to the PWM ports on the Digital Sidecar. They must not be connected to speed controllers or relay modules.
If used, the compressor must be connected to one and only one approved relay module.
Each other electrical load (motor or actuator) must be supplied by one and only one approved speed controller, or one and only one relay module.
Electric solenoids may alternatively be supplied by a Solenoid Breakout Board connected to the NI 9472 cRIO module, which is powered by 12V.
As for the Spike, I'm not sure.

I remember hearing/reading about it being one, and it seems to behave like any electro-mechanical relay I've used also. (Mainly, the clicking sound when it switches)
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Unread 22-04-2012, 18:16
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Re: paper: Shooter Wheel Speed Control

Quote:
Originally Posted by nighterfighter View Post
I think the rule violation would either be... Or, more likely this one...
Neither of those rules seem to apply unambiguously in this case. The first rule you cited arguably doesn't apply ("custom circuit") and the second rule explicitly allows a Spike to be used to control certain motors.


Quote:
(Mainly, the clicking sound when it switches)
Well that seems like a dead giveaway. I've never listened to one. (And if I had, I probably couldn't hear it anyway).



Last edited by Ether : 22-04-2012 at 18:36.
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Unread 22-04-2012, 18:21
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Re: paper: Shooter Wheel Speed Control

Quote:
Originally Posted by nighterfighter View Post
because a Spike is a mechanical relay, don't they have a limit as to how quickly they can switch to ON/OFF?
Yes, I would think so. See footnote2 on Page1 of Rev C of the paper.


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