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?
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.
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.
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!
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!
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.
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.
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.
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?
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?
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.
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.
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:
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.
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…
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.
