FlyWheel Prototype Help

[broluwo]

Hi guys! 449 here, we have been prototyping a flywheel design and we have come across a small problem that we don't quite understand. We first used a handdrill to power our flywheel and the ball went about 7 feet. Next we changed the motor to a 16:1 Geared BaneBot motor; we expected the ball to go farther since the motor was faster but the distance covered didn't change. We don't know why this is the case. Any idea or advice is greatly appreciated. Do you think it's a problem between the ramp and the ball or it is just a ramp angle problem (or anything else)? Thanks very much.

[MrForbes]

I would really help to see some pictures of your setup, video too if you have it.

[pilum40]

I'm keeping tabs on this thread as I'm prototyping our "shooter" today.

Thanks!

[maddoctor90]

One possible situation is that your wheels are not gripping the ball very well. Thus speeding it up may just equate to the wheels slipping more and thus less force being applied to the ball.

[broluwo]

http://www.youtube.com/watch?v=hmgRfT4Kvxg&context=C3f259d3ADOEgsToPDskJH VJsffJdoRbm6llz3BmsI&safety_mode=true&persist_safe ty_mode=1&safe=active

Here is a video of our testing. It's not a close up, so we will follow up with a closer photo shot. The white back used is the back of regolith (used in 2009 Lunacy)

Thank you again!

[sdcantrell56]

Try more compression

[KrazyCarl92]

To understand how to prototype a flywheel design you should first understand the physics behind them. The fly wheel is intended to convert the angular momentum of the wheel to linear momentum in the ball. Ideally, the change in angular momentum of the fly wheel (decrease) is equal to the increase in linear momentum of the ball.

The formula for angular momentum is L = Iw, where L is the angular momentum, I is the moment of inertia (of the wheel in this case) and the w (actually omega) is the angular velocity of the wheel. The formula for linear momentum is P = mv, where P is momentum, m is the mass of the ball, and v is the velocity of the ball. Since the moment of inertia of the wheels and the mass of the ball don't change, we are simply concerned with the angular and linear velocities. Increasing the change in angular velocity of the wheels will in turn increase the change in linear velocity of the ball. One way to do this would be increasing compression between the backing and the wheels. This will transfer more of the energy stored in the angular momentum of the wheels to the balls, which is what you are looking for. The wheels should slow down significantly when the balls go through the shoot.

The more the wheels decrease in velocity, the farther the ball will go. More torque applied to the wheels via the motor will help with reload time (getting the wheels back up to speed after firing), but may not do much for increasing the distance or speed.

(My explanation above ignores the effects of angular momentum increase in the ball due to spin, but it still holds mostly true I believe.)

[broluwo]

https://mail.google.com/mail/?ui=2&ik=0c7da1b6d2&view=att&th=134d8e67d0e48399&a ttid=0.1&disp=thd&realattid=1390924362618503168-1&zwhttps://mail.google.com/mail/?ui=2&ik=0c7da1b6d2&view=att&th=134d8e67d0e48399&a ttid=0.2&disp=thd&realattid=1390924362618503168-2&zw These are the photos of our prototype. We'll try compressing it next, and then we'll try using less compression to see how well it works, and we will get back to you.

[jreuter]

As maddoctor said, it sounds like the wheels are already slipping through the entire contact with the ball. If I recall correctly, the force on the ball is the normal force x the dynamic coefficient of friction. Spinning the wheels faster doesn't change either of these. As someone else implied, increasing ball compression will change the normal force, and you should throw farther, with more transfer of kinetic energy from the wheels.

[WileyB-J]

Here's a picture of our current prototype. Check your compression and try not to alter the velocity/trajectory too much after it is past your wheel launcher, it tends to slow it down a great deal.

And this is it in action: http://www.flickr.com/photos/wileyb-...n/photostream/

[gbalcita]

Consider the distance the ball "rolls" along the guide while in contact with the wheel. The longer the distance the more energy lost to "rolling drag". Try reducing the contact time/distance. Also, you are pulling the ball up. Is there a way to feed the ball such that it is pushed/pulled from left to right vs. from bottom to rightalmost level to the wheel

During this rolling stage the ball looses a lots of energy/momentum. I think the drill's power rating compensated for the lost momentum and the banebot motors lost a lot of the momentum to the "rolling effect".

If the wheel was slipping against the ball then more compression should transfer more power. If you increase compression I recommend reducing contact time (noted above) to minimize energy loss. If the ball was not slipping, then more compression will result in no benefit or increased "rolling drag" along the guide.

Hope this helps.

[dellagd]

Try switching out the wheels to ones with more friction.

Are there skid marks on the ball? You arn't getting any spped increase because the increased speed is just reducing the amount the wheel can grip the ball. These factors just cancel so the ball kind of hits a point where it wont go any faster and go a greater distance.

I mean, just think about it. If the wheel is going faster, then it would have to grab more the pull the ball with it (Since the ball has inertia and resists the acceleration) All the wheels force is being imparted via friction, and you have reached the max amount of force the wheel can impart with the amount of friction you currently have.

Compression would help. Try those wheels that have that orange rubber blunt-spikey stuff on it. Lets see what those do to the ball before you even add more compression

[TEAMROCK2000]

try cutting a little bit of the end of the board part its hitting the board last u dont want that u want it touching the wheel last.

[EricH]

Originally Posted by TEAMROCK2000

try cutting a little bit of the end of the board part its hitting the board last u dont want that u want it touching the wheel last.

Speaking from experience, that isn't entirely the case. You probably actually want them to break contact at almost exactly the same time. But, I have seen at least a couple of long-range shooters that used a low wheel and a high release point to shoot--the ball went up a somewhat parabolic ramp.

Having the ball release off a backplate isn't a bad thing if you do it right--you just change the speed and angle and spin by having it go off the plate last as opposed to releasing off the wheel last. Oh, and releasing off the wheel last may have its own problems, like reducing spin.

It's all in the setup.