This year we went with a fixed angle double flywheel shooter optimized for fender shots into the high goal. Our compression is 1.5" and our shooter angle is about 13 degrees. We’re using 4" Coulson wheels as our shooter wheels. During practices and at the NY Tech Valley regional we had very good accuracy. At the regional, I’d estimate we were in the top 5 or so for accuracy into the upper goal. (Just a gut feel, I haven’t looked at our own scouting data).
When we got the SPBLI #2, our accuracy fell off somewhat. Still reasonable, but not as good as we had come to expect. We even had an occasional jam in our indexer which wasn’t something we’d experienced since our very earliest testing. What we noticed is that many of the balls were noticeably egg shaped. It was apparent visually but also when watching the field get set up. You could see balls rolling oddly away from where they were placed. I suspect (but don’t know for certain) that many of the game pieces had some miles on them from the previously completed SPBLI #1 and were just showing their age. We made some minor changes to where the ball handed off to the shooter, which eliminated the occasional jamming but accuracy really didn’t improve much.
I’m not here to complain about the game pieces. Nothing in the rules promised any sort of required degree of roundness and designing for less than perfect game pieces is part of the challenge. What I am wondering is what measures did other teams take when designing their shooters to help make them more consistent even when faced with less than optimal game pieces?
If you find egg shaped cargo let the Field Supervisor or FTA know. We’ll replace ones that are noticeably out of round.
Game manual: "RAPID REACT is played with oversized tennis balls called CARGO, custom modified for FIRST by Flaghouse. "
I would expect a very spherical shape in the common interpretation of “tennis ball” I would say that anything visually egg shaped or a cargo that doesn’t roll straight doesn’t meet that definition. And as @BBaltrusch said, mis-shapen cargo should get requested to be replaced (before the match)
Also in the manual: “The oversized tennis balls used as CARGO are not manufactured with any
tight tolerance. Wall thickness, surface pilling, and shedding may vary.”
Deformation of shape is much more drastic than “Wall thickness, surface pilling, and shedding”. I would expect teams to design around “Wall thickness, surface pilling, and shedding” but not egg and sphere shaped cargo.
One of our initial (KoP) cargo (the blue one) was definitely egg-shaped. So we started from the premise that we’d end up having to deal with that sooner or later during the season. As a result, we designed our intake to use long poly-belt flappers to do the main job of pulling the cargo in, which is very adaptable to whatever shape they have. Then our indexer/tower has stacked compliant wheels that get larger towards the outside of the cargo path and have about an inch of compression. Finally, we went with 1 1/2" of compression between our shooter wheels to make sure we’d get consistent shots no matter the cargo shape. It’s all worked out pretty well.
Aside from the milk crates in 2018 and the hatches in 2019, these are the most consistent game pieces we’ve had in years. The 2019 balls were very prone to over-inflation by several inches, and 2020/21 balls were drastically different depending on how used they were. By comparison, these have been easy. But obviously toss the eggs out.
That being said, we largely deal with them by not going for the long shot. Fender shots mean your target is has the largest margin for error. I know several other teams that fully intended on shooting while far from the fender, or even shooting while moving, and they’ve converted to fender shots because it’s that much more accurate.
We used catapults, so ball condition really has no impact on launches. That design decision was driven by fear of varying ball behavior throughout an event (2020 memories) and concerns with bounce-outs due to spin.
We built a prototype with several adjustment capabilities in it and tested with cargo at inflation levels from below min to above max and made adjustments to our design so we we could accommodate the most variation possible within that window of pressures.
We did this because we have a history of seeing field crews be wildly inconsistent with inflatable scoring objects, the worst issues being tube inflation in 2007 when the field crew was intentionally overinflating the tubes at our first event and it wasn’t until we talked with other teams that were also having issues that we figured out what was going on. That taught us the important lesson to not design assuming the field crew will do things correctly.
Not totally true when we complained that one of the preload balls was flat they just gave us another ball from the field. It really didn’t make sense as we had a 2 ball auto and the ball they swapped was our 2nd auto ball.
We handled this with lower compression and a lot of contact time in the shooter to create a gentler acceleration. Specifically we broke the shooter into separately driven stages and tried to pack most of the acceleration into the early stages and let the later stages “trim” the velocity to a more precise value.
The low compression accomplishes two things directly: minimizing ball rebound and minimizing mechanical loads on the shooter. The latter is pretty simple, the balls are hard and deflection in the shooter is generally bad for accuracy (both because of wear and just everything wobbling around when a ball goes through). The former is based more on an intuition for which I have no experimental evidence. With higher compression the ball rebounds to its original shape immediately after leaving the shooter, this causes the ball to react off of the shooter hood and shooter wheel in weird ways. As far as I can tell this is the cause of a lot of the inaccuracy in many shooters so reducing compression helps. Obviously reducing compression reduces acceleration which in turn means you have to increase contact time and thus shooter size.
This topic was automatically closed 365 days after the last reply. New replies are no longer allowed.