Topspin and bounce out

Can anyone with access to the official high goal comment on the effectiveness of shooting with topspin in order to decrease bounce out? I have been reading about this (thread 1 and thread 2) but I haven’t been able to find anyone that actually tested with topspin.

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Unfortunately not, will likely have more data on that soon. I can say backspin caused a lot of issues with balls bouncing out. I’d say 125 probably had the most dialed in shooter at the event which was beautiful to see. They had a flywheel as well as another top roller to help with shooting. For some data, we shot 163 balls at week 0 total, and 17.9% bounced out. It doesn’t seem like a lot, but it defo made a difference. Teams with access to a real hub are gonna be at a huge advantage imo.


If backspin had such a bad effect, then I am optimistic that topspin will be at least decent.

Do you know if they had any spin at all on their shots? How far away did they typically shoot from? How many of their balls bounced out?

Definitely. Teams that can’t shell out $800 for an exact replica of the goal definitely shouldn’t be at such a big disadvantage like this

I believe backspin hurts if you hit the near side of the hub, and topspin will hurt if you hit the far side of the hub. I may have that backwards though. The spin just forces the ball to go down or up depending on which side of the hub it hits.

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You do have it backwards. Hitting the far side of the hub with backspin causes the ball to shoot downwards - the rotational energy is converted into translational energy, making the ball move faster towards the bottom, which can cause it to then bounce out. That’s what makes backspin on a basketball so effective - you hit the backboard and instead of bouncing out, it bounces down towards the basket!

Hitting the far side with top spin has the opposite effect - the angle changes upwards, but now that rotational energy is acting in the opposite (ish) direction the ball was traveling, which means the ball ultimately slows down when it hits that far side of the hub. Of course, if you hit the near side al of this is reversed!

Given the size of the goal and the arcs imposed by the dimensions of the field and the height of the goal relative to the robot, I imagine most shots are going to hit the far side. Naturally, all of this assumes you land the shot inside the goal. Rim shots are a whole different story!


I wonder if a bit of sidespin would help balls stay in. Would maybe direct them to roll around inside a bit as the energy dissipates


Yeah, in general, it seems spin is bad. Which is why there was a lot of talk on top-rollers around late-week-1/week 2 of the build season.

In previous years, you wanted as much power as you could get, which also usually translated to reducing backspin. This year, seems like you want just enough power, still with minimal spin.


Who needs a turret if you can just throw accurate curveballs? Now THIS is an approach I’d like to see.


It does IMO from testing, it’s just more irritating to package


Sidespin should be roughly analogous to just hitting off-center. By deflecting some velocity outside that XZ plane you reduce the energy available on the secondary bounce to eject the ball outright.

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This is what we found as well from tuning our shooter on our (far from official) hub. If you aim for the middle of one of the sloping sides of the hub rather than the center, the ball bounces sideways into the goal rather than directly up and out.

Our vision system right now recognizes the center of the target. We’re still working on how to get it to aim slightly to the side, but not too much that we end up missing the goal altogether.

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Maybe it will shoot to the side of the goal if you do a drive-by shooting?

Bumping this thread since we are few weeks into the season now. Has anyone tried topspin at an event?

We did. It worked well when we would hit the back side of the goal, but poorly if we hit the front side or wheel. We’ve already made a change to remove all spin for our second event.

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Were you shooting with a ton of arc or why were you hitting the near side? How far were you usually shooting from?

We used a topspin shooter at our first event and it worked great, the only bounce-outs we encountered were due to hitting the center wheel, though we’ve been working to resolve this as well. Here’s a video of one of our matches Triple Helix week 1 high scoring match, 116 points - YouTube.

With our bumpers crossing the back line of the tarmac, so a fairly close shot but not right up against the hub. We also had too much power in our shot at the time (too high of an arc, but not ridiculously so). You can see 3 bounce-outs in this match:

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