How Spin Affects Fuel Trajectory

[JohnFogarty]

In designing a flywheel shooter with my students I've come across something I'm sure many of you have or will discover. Spin causes some pretty weird things to happen to the fuel as they are in flight to their destination.

What I'm looking to do is increase consistency in my shots and I've already got pretty tight control of the RPM of the flywheel.

This suggestion was mentioned by another mentor that works with my team and I wanted to pass it along for thought and clarification as I work today.

Apparently when you use a flywheel shooter with just a backplate as the arc/curve you lose some of the energy and get less consistent flight paths with the balls because some of the energy you are trying to impart on the ball as kinectic energy is lost as rotational energy....ie spin on the ball. So the idea is instead of having a curve of plastic you instead have a arc made up of a bunch of small wheels, rollers, something of that sort so that you balance out the rotational energy and the ball simply flys up with no backspin....which could be a good thing especially with the fuel balls. The only reference design where I noticed a team had thought of this and were succesfully able to counteract the spin from their flywheel was team 1717 in 2014.

https://www.chiefdelphi.com/media/im...fe76bdff_l.jpg

I'm not an ME so I hope I'm not explaining things too incorrectly, but I thought this was interesting.

[Mark Westwig]

Team 639 is prototyping a very similar type of shooter. Our left to right consistency is within a half of a foot every shot, but our front to back is all over the place. We were using an 8" rubber treaded wheel for ours, can I ask what type and size wheel you were attempting it with?

[Mike Schreiber]

Originally Posted by JohnFogarty

In designing a flywheel shooter with my students I've come across something I'm sure many of you have or will discover. Spin causes some pretty weird things to happen to the fuel as they are in flight to their destination.

What I'm looking to do is increase consistency in my shots and I've already got pretty tight control of the RPM of the flywheel.

This suggestion was mentioned by another mentor that works with my team and I wanted to pass it along for thought and clarification as I work today.

Apparently when you use a flywheel shooter with just the the a backplate as the arc/curve you lose some of the energy and get less consistent flight paths with the balls because some of the energy you are trying to impart on the ball as kinectic energy is lost as rotational energy....ie spin on the ball. So the idea is instead of having a curve of plastic you instead have a arc made up of a bunch of small wheels, rollers, something of that sort so that you balance out the rotational energy and the ball simply flys up with no backspin....which could be a good thing especially with the fuel balls. The only reference design where I noticed a team had thought of this and were succesfully able to counteract the spin from their flywheel was team 1717 in 2014.

https://www.chiefdelphi.com/media/im...fe76bdff_l.jpg

I'm not an ME so I hope I'm not explaining things too incorrectly, but I thought this was interesting.

Traditionally teams will intentionally put backspin on a ball to get more air time without the ball dropping into the goal. The spin energy you're putting into the ball helps create lift on the ball due to the magnus effect. This can help to increase shooter accuracy when aiming in a vertical hole in the wall because you have a flatter trajectory. Shooting into a horizontal hole with a ball that has holes means your mileage may vary.

[matthewdenny]

I believe that normally backspin will cause the object to take a flatter flight path (which would make scoring more difficult). Perhaps forespin would cause it to drop.

[ThaddeusMaximus]

1717's shooter is powered on the backspin. If the rollers spin freely, ball will just simply spin freely without going anywhere.

The hood imparts a force and must do that in order to get the ball out, otherwise you're just exerting a torque on the ball.

[JohnFogarty]

Originally Posted by ThaddeusMaximus

1717's shooter is powered on the backspin. If the rollers spin freely, ball will just simply spin freely without going anywhere.

The hood imparts a force and must do that in order to get the ball out, otherwise you're just exerting a torque on the ball.

Check out a video of their robot shooting the ball. It flies with no spin at all.

[Chris is me]

Originally Posted by JohnFogarty

Check out a video of their robot shooting the ball. It flies with no spin at all.

That is evidence in favor of his claim, not against. The ball not spinning is a consequence of it being shot from two wheels both moving at the same speed.

For everyone else in this thread: Almost all answers here in this thread are going to be based on prior experience with balls, which have usually been foam balls or inflatable balls. These do not necessarily apply to these balls! Do your own testing to see what spin does to these balls, as it is definitely not exactly the same as 2016 for example.

[JohnFogarty]

Originally Posted by Chris is me

That is evidence in favor of his claim, not against. The ball not spinning is a consequence of it being shot from two wheels both moving at the same speed.

For everyone else in this thread: Almost all answers here in this thread are going to be based on prior experience with balls, which have usually been foam balls or inflatable balls. These do not necessarily apply to these balls! Do your own testing to see what spin does to these balls, as it is definitely not exactly the same as 2016 for example.

That makes it clearer as to what he meant. I understand now.

[Lennie]

I can confirm as ex-mentor of the now defunct Team 1717 that both the front and back wheels were velocity controlled (so we could control the spin on the ball). As the post below states this years game uses much smaller "whiffle" balls so there are likely major differences.

I am now mentoring team 5818 and we are looking at a "wheel" shooter as well.