Re: Problems with tuning shooters using AM basketballs on Practice Field?
 

They might be, that's considerably more torque/inertia than our shooter.

What I like best about the voltage control is that there is no tuning involved, set it once and don't worry about it after that.

Re: Problems with tuning shooters using AM basketballs on Practice Field?
 

We have a single 8" kit wheel driven by a single powerful FP motor. We seem to spend a lot of time waiting for the thing to settle down, we could probably shoot a few more baskets with the simple voltage algorithm. I posted a link to this thread on our team fb page, our programmer should see it.

Ironically today he's doing his science fair project report on the feedback speed control system :rolleyes:

Re: Problems with tuning shooters using AM basketballs on Practice Field?
 

We're using 2x two 8" wheels on 1/2" shafts with AM hubs driven by AndyMark motors and Andymark 3.67:1 planetary gearboxes, and our PID is quite stable -- we fed both old and brand new balls through it and it was consistent except for once in a while... The compressibility of the ball didn't seem to influence the throw much.

...I hope that pans out!

Re: Problems with tuning shooters using AM basketballs on Practice Field?
 

Could you explain to someone ignorant why controlling with voltage is so much better than PID? I would think that you want constant rpms on the shooter wheels for maximum consistency. More success with a less sophisticated control system seems a little counter-intuitive to me...

Re: Problems with tuning shooters using AM basketballs on Practice Field?
 

You're right...except that some of us seem to have built systems that are very difficult to get reliable speed control with. In that case, a consistent open loop system could work better.

Re: Problems with tuning shooters using AM basketballs on Practice Field?
 

PID is a good solution but it is not magic. The software is only one part of the servo system. In this case one can tune the wheel to free rotate at a selected speed but not have enough gain to recover quickly when a ball slows it down. So one might try to raise the gain. But then the higher gain might create an under-damped or oscillating condition when there is no load.

One approach is too build mechanical gain into the system by using stronger motors or storing energy in a flywheel etc. This gain would have much less phase delay and be more stable (I hope).

HTH

Re: Problems with tuning shooters using AM basketballs on Practice Field?
 

In a perfect world, a perfectly tuned super-fast PID control would be better than just about anything else. However, an open-loop voltage control scheme works well enough for what we need to do in FRC without requiring any tuning at all. This control has gotten 95 in the top 5% Hybrid OPR.

I think this is definitely a case of "the best is the enemy of good enough." At least for my team this year.

Re: Problems with tuning shooters using AM basketballs on Practice Field?
 

interesting...we're a couple above you with closed loop! But I still think we should give open loop a try.

Re: Problems with tuning shooters using AM basketballs on Practice Field?
 

Based on this thread, we are definitely gonna have both approaches ready to go!

Re: Problems with tuning shooters using AM basketballs on Practice Field?
 

Hrm, quite interesting. I don't understand the OPR completely, but it seems like it can be skewed by alliance partner performance, either up or down.

For what it's worth I'd call our autonomous 70-80% reliable, with a large amount of our misses coming from shots spaced too close together where the second ball bounces off of the first. A delay between hybrid shots will be implemented for the Hartford regional.

Re: Problems with tuning shooters using AM basketballs on Practice Field?
 

We have a really long delay between shots, waiting for the shooter speed to adjust. Open loop could really speed up our shooting process, hopefully enough to get a few more shots off in teleop

Re: Problems with tuning shooters using AM basketballs on Practice Field?
 

We also have a driver enabled adjustment button. Each click of the button decreases (or increases) the voltage applied to the shooter by 1/10th of a volt. This results in a decreased (increased) RPM of ~100. So if we find we are overshooting by 5 feet, the human shooter knows to decrease 3 clicks based on data collected during practices.

The problems that are often outside of our control (like ball squishy-ness) are the most valuable learning tools! Thanks, GDC!:)

Re: Problems with tuning shooters using AM basketballs on Practice Field?
 

This was a HUGE problem for Team 20 this past weekend at GSR; we went from a 60% shooter in practice to a 3% shooter. Our targetting was working, but we were over shooting the hoop by 4 to 5 feet every time. Come to competition with a plan in place to account for the difference, or you will be sorry.

Re: Problems with tuning shooters using AM basketballs on Practice Field?
 

Is that a written report? If so, could you ask him if he'd be willing to post it?

Re: Problems with tuning shooters using AM basketballs on Practice Field?
 

Are there any teams who attended a week 1 event who didn't have an issue with this?