# 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 â€śpushesâ€ť a ball upwards, making for a shallower arc, while top spin â€śpushesâ€ť 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 â€śeither sideâ€ť, do you mean top and bottom, or left and right?

While not always transferrable between games, thereâ€™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 â€śtossâ€ť 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. Itâ€™s kind of neat.

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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 30â€™ distance. We didnâ€™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 donâ€™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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