Double roller prototypes?

Anyone have any videos of launching balls with a roller on either side and what happens if one is significantly faster than the other?

We only have two students working on prototypes this year so we have to do a lot more research before committing time to builds.

No videos, but we had a shooter like that in 2012 (which was not the right choice for that year!). Our wheels were top/bottom, not side to side, though. We could change the spin by changing the speeds of the wheels, which would noticeably change the arc of the shot (backspin “pushes” a ball upwards, making for a shallower arc, while top spin “pushes” it downward).

If your wheels are on the sides of the ball, I would expect a difference of speed would essentially create a curveball, sending it to the side that is slower.

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When you say “either side”, do you mean top and bottom, or left and right?

While not always transferrable between games, there’s been a lot of usage of wheels or rollers in both those configurations for various game pieces, and knowledge is somewhat transferable. With top-bottom rollers, you get a “toss” of the ball that has basically no spin on it - if energy is transferred perfectly (it never is!) then for a given roller diameter and RPM, two rollers would shoot the ball twice as fast as 1 roller + a stationary piece. As you vary the speed, the exit velocity of the ball theoretically decreases, and the spin placed on the ball changes. A faster bottom roller will give you backspin, which tends to help the ball rise up and stabilize / smooth the trajectory. It can also make the ball bounce less forward after landing. Topspin tends to make a ball cut downwards / fall, and bouncing is more energetic / forward.

The tradeoff with almost any double-roller shooter solution is that you get limited contact with the ball - usually only at the moment the ball is in contact with both rollers. A one-wheel or one-roller shooter can contact the ball for longer as it rolls along a shooter hood. In recent years, teams have experimented with combining a top roller with a shooter hood, so that the ball contacts the bottom roller for most of its travel and then the top roller jumps in at the end. It’s kind of neat.


We did a prototype of a double wheeled shooter (side/side) in 2020 and I might find some video somewhere. It basically knuckle balled everything, but the shot variation was no more than a couple of feet over a 30’ distance. We didn’t use it in the end because we wanted to hit the small target.

We used a double wheeled shooter (left and right orientation) on our 2020 robot. (Team 2358 Bearbotics) I don’t remember which of our two competitions happened and which was cancelled. But there should be video available on blue alliance. We go to Central IL and Midwest.

Inconsistent speeds produce a curve-ball effect.

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