Problems with tuning shooters using AM basketballs on Practice Field?
 

I heard about 20 minutes in to this podcast that teams that tuned their shooters using their own AndyMark basketballs on the practice field encountered tuning issues when they used competition basketballs on the real field.

A speaker in the podcast states that, while their shooter worked perfectly with the balls they used on the practice field, it consistently overshot the hoop when they played on the actual field with the competition balls. The other commentators confirmed this phenomenon as being real.

Have any other teams encountered this issue at any of the past few regionals?

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

I can confirm that we had balls in our shop of varying densities and wear and tear. A new ball would shoot a good 5 feet higher than an old worn out one. Regardless of this, our plan is to re-calibrate our shooter when we get to the event, with whatever kind of ball they have there.

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

You might also note that the practice field tends to be the graveyard for balls that are killed on the competition field.

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

We were having this problem as well at GKC. In practice we would tune our PID setpoints until the ball would make it into the hoop every time, and then when we went on the competition field our balls would overshoot.

We were also using one of our first balls that has suffered some wear and tear. I'll have to remember to bring a newer ball with us to our next regional.

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

We noticed our shooter accuracy getting worse as the regional progressed...one of the possible reasons is the condition of the balls becoming more different as they are used longer. But we have other things to worry about too, like our shooter getting wonked when the robot falls off the bridge (which only happened about 4 or 5 times)

This game has some good challenges, excellent job GDC! :)

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

The balls on the field were definitely much denser than any of the balls we had been practicing with. We even reserved some brand new balls for practice on the final days of build season, and the balls at the event still flew much further. I do not have a great explanation as for why, since all balls with the FIRST logo are apparently from the same batch. I will say that if you bought balls directly from Gopher Sports, the FIRST balls have both a different density and a different surface finish.

As the event went on, balls were worn/damaged but still (in my opinion) seemed to shoot further than our shop balls.

It's all part of the challenge. Some types of shooters are more susceptible to amplifying ball variation than others. At least one team - 1218 - rigged up a sensor to measure ball squishiness and fed the result to their shooter speed control system.

The most straightforward thing you can probably do about it is make it easy to adjust your shooter to the variation. Use a configuration file to read in new speed setpoints without requiring recompiling code. Or give your drivers a trim wheel to add or subtract from a nominal motor/wheel speed. You will probably get between 1 and 5 practice matches at your event. You want to be able to dial it in in that time!

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

We have a trim control for ours. But I still think our shooter speed control algorithm is flaky, on top of everything else....

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

we ran into the same thing

we are using single wheel shooter with a stationary pinch bar to compress the ball into the spinning wheel makes for lots of backspin. The video link is what we found with the worn balls vs. new balls. the issue seams to be the compression reaction more than the surface wear. the new balls will take effort to move the air out of while used balls have lots of little nicks and cracks for the air to escape out of thus the force to compress is much less.

Our solution was to reduce the amount of pinch on the ball this limited our distance but greatly increased our consistency from one ball to the next.

http://www.youtube.com/watch?v=4EueP...eature=channel

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

That sounds like a good explanation of what's happening.

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

This.

We had a consistent shooter in our shop, then decided to try to increase our range by increasing the compression. This greatly reduced our accuracy. We bought a new ball and tried to shoot it; it sailed a couple feet higher than all the old balls we were using. We concluded that the added compression was hurting us.

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

We've been using an open-ended voltage control (same as 2006) for our 5-roller shooter and were very consistent throughout GSR. Even when fresh balls were put out on the field during eliminations our hybrid was as consistent as before. FWIW I think we're ranked 20-something in Hybrid OPR.

Our program essentially does this:

shooter_speed = 11/system_voltage

We tried a PID loop but couldn't ever get it to behave the way we wanted it to. The issues being that there are huge changes in friction and system inertia when a ball is engaged with the shooter, and our shooter system is slow low-inertia that the PID loop is unstable when under no load no matter how much we tuned it.

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

I'm thinking that this is a good solution to part of our problem. I wonder what the odds of us being able to implement new code on Thursday (AZ regional) are?

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

So a gain that made it stable with no load did not compensate for the change in load when compressing a ball? Then raising the gain to help made it oscillate under no load? We might have the same problem... what motors do you use?

For teams incorporating a compensation factor - was the factor a simple constant or a constant multiplied by V or maybe V squared?

TIA

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

Very high I'd bet. Our student programmed disabled the PID loop and added the voltage control in 10 minutes. I'm no expert, but it seemed very simple.

I believe that's what was happening to us. We're using two RS550s for our shooter. PIDs might work better for other teams with higher-inertia shooters. Our shooter consists of five 4" long rollers made from 0.065" walled aluminum tube, there is hardly any mass/inertia there. We couldn't even get a stable no-load PID loop, it was causing some seriously scary motor arcing.

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

Our shooter uses 2 AM 8" FIRST wheels driven by 2 FP 0673 motors and 2 AM 9015 motors. I was hoping having a lot of torque to spare (the motors barely get warm to the touch) might make it more reliable/tunable - we'll see I reckon.