Hey guys, I’m currently designing a flywheel shooter, and was wondering if there were any guidelines to how much compression to aim for. Increasing compression increases both the normal force of the ball, and the deformation, which leads to more contact area, however it also relies more on the inconsistent compression of the balls, so I would like to not have excessive amounts.

At the moment I am aiming for about 1.5" to 2" of compression on the ball, do you think this would be acceptable?

The ball will be in contact with the rollers for about 12.5" of travel. (Approximate Center of Mass travel)

Honestly, I would only recommend as much compression as you need to get the width of contact patch your shooter requires, and no more. If you have high speed AND high normal forces, you might repeatedly leave marks or scuffs on the ball. This is illegal per [G12]. Additionally, the force required to compress the ball will cause the flywheel to slow.

We’re getting repeatable results with much, much less compression.

Why would you compress it any more than what you need? What advantage do you gain in power or precision by compressing the ball? Ergo, compress it only as needed. There’s no specific amount; it will take prototyping. My recommendation is to measure the ball uncompressed, push it in with your palm to compress it just until the contact patch firms up a bit, then measure again. Start with that, then adjust in small amounts for your specific shooter.

Prototype a design that has an adjustable compression (example: http://www.youtube.com/watch?v=DO0XzkthMUs), and find what works best for you. A pitching machine design I built achieved accuracy up to about 20’ with roughly 2.5-3" of compression. That being said, most shooters are different so it will take prototyping to find your ideal compression rate.

I will be doing some tests on the ball today to find out how much force it takes to compress the ball X amount, and how that relates to the torque required on the motors running the shooter. I will try to post the results on this thread later. Maybe as a formula. Stay tuned!

I did some testing yesterday. it appeared the ball had about 7 lbs/inch of compression, this was pretty linear up to 3 inches where I stopped measuring. This was between two flat surfaces though, so i’d expect a different (lower) value if you had a single wheel or were riding on rails with the ball.

I wonder how this compares to other teams measurements?

As promised, here are the results of the tests on ball compression. And how to use them. I took a pressure plate and placed the ball on top, and rigged a system where i could lower a surface in half inch increments and measure the force on the ball. Here is what i got. I would encourage other teams to try it out for themselves.

0.0in 0.0 N
0.5in 22.3 N
1.0in 45.8 N
1.5in 66.5 N
2.0in 90.4 N
2.5in 112.6 N
3.0in 127.6 N

If you want to know the torque needed on the motor, use this formula:

Torque = Force of compression X Radius of the shooter wheel X The compressed coefficient of friction between the ball and the shooter.

we have a 1.5"-2" compression for our shooter prototype and we found no real difference between that range.
1" didnt have as much distance/power as it left our shooter through repeated tests.

Different designs will have different optimal compression requirements.
Best to test it out and see for yourself what will work best.

We determined experimentally that 1.5" of compression with nominally 1.5" diameter rollers worked pretty well. It is encouraging to see other teams getting the same numbers!