How do I pick a fly wheel?
 

My team wants to use a fly wheel, but we can't decide on what weight and size it should be, and where to get it. We have a possible machinist, but it is not definite. Please help, we really need to figure this out.

Ryan, Team 435

ps. We also debated using two fly wheels below the ball, vs one below. Thoughts?

Re: How do I pick a fly wheel?
 

The best way to decide is to prototype.
Try different combinations of wheels and motors, different gear ratios, etc.

Prototype.

Re: How do I pick a fly wheel?
 

We would love to prototype. Unfortunately, you need parts to prototype. We have little left in our budget, and our vast array of wheels are mainly misfits that aren't much use for anything. Even if we had money, It's getting a little late in season to make orders for test parts

Re: How do I pick a fly wheel?
 

Have you tried adding weight to any of the wheels you have and tried ways to make those work?

Re: How do I pick a fly wheel?
 

A wheel is a wheel is a wheel.
Prototype.

You telling me that nobody on the team has access to ANY wheels at all? Borrow from a lawnmower, hand truck, your little sister's bicycle, whatever.

Even a circle cut from wood is a wheel.

Re: How do I pick a fly wheel?
 

Team 975 once made an effective ball shooter wheel out of plywood disks glued tgether. It was about 10" in diameter, 3" or so thick and grooved somewhat like a pulley. It had enough weight and could easily be drilled out to adjust weight.

Re: How do I pick a fly wheel?
 

Team 868 did something similar in 2010. Not shown, we used rings in the center part instead of disks to save weight.

Re: How do I pick a fly wheel?
 

We had a saying, "Wood is Good". Mostly because we had no budget our first year and no machining facilities. I still have the promotional sign. It was painted on a scrap of Cedar wood siding: "Team 975 - Featuring W-Fiber."

It's available, "green" and is a remarkable material. Earlier this year, I went to see a local flying circus. They are still flying airplanes with wooden frames dating from the late 1920's and early 30's. Not just flying, but doing loops and stalls. :ahh:

Re: How do I pick a fly wheel?
 

Wood is also easier on the tooling side of things too. Wood tools are less expensive, more common, and (usually) aren't so easily worn down like Aluminum.

For a flywheel, you don't have to attach the weight to the shooter wheel itself. So long as the flywheel is attached coaxial to the same live axle as the shooter wheel, you can use whatever material you want. Just be sure it's balanced or else it's rip itself apart at high RPM's. A good hardwood, 1/2-3/4" thick, and some 3/8" bolts might do the trick.

Re: How do I pick a fly wheel?
 

Below is a PDF created by our lead design engineer detailing how we have made a first cut at determining the size of our wheel.
We like to do the math first and then build a prototype.
Let me know if you have any questions.

It is a relatively simple angular problem... we have made a few assumptions.

thanks
and good luck!!

Re: How do I pick a fly wheel?
 

Bob – great work by your lead design engineer figuring out the relationship between the loss of wheel inertia and the transfer of energy to the ball. It puzzled me though, the idea that we could choose the rpm loss of the wheel to be 250 – that didn’t seem like an appropriate input to the problem. What if I chose 300 – how would the answer be different?

After some thought, I realized that the kinematic relationship between the velocity of the ball (300 ips) and the final rpm of the wheel was not captured. The wheel inertia formula assumes that just the right amount of energy is transferred to the ball to achieve the target velocity, but how that is controlled is not presented.

In our team’s shooter design, and probably like many others, we are accelerating the ball by a drive wheel on one side so that the surface of the wheel and the surface of ball are traveling in unison at the time of release. So that creates a kinematic relationship – the center of the ball is traveling at 1/2 the velocity of the surface of the wheel. For a 6 inch pitching wheel, that would require the rotation to be around 1900 rpm to achieve 300 ips in ball velocity.

I think the input values can be tweaked to accommodate matching the ball speed to a corresponding wheel2 rotation. That would tell us the initial wheel1 rotation speed needed to achieve the target ball velocity for a given wheel inertia. That seems like something we can control.