I’m working on designing a dual flywheel shooter that will shoot ball game pieces from a previous game (don’t remember the year).
While working on the gearboxes, I was curious as to how much speed (rpm) and torque the flywheel would need. The game piece is light and would be mildly compressed, probably by Andymark’s Compliant Wheels.
Does anyone with experience with this know just an estimate or way to determine these numbers?
One of the best things you can do design wise is to match the peak power output of your shooter motor to the output flywheel speed. If you are using a CIM motor that means you want your motor output speed to be 2670 RPM when your shooter is at the speed you want. This is generally done so that the flywheel recovers from each shot the fastest and is ready to shoot again.
Was just going over how to do this with some students. I wrote up some notes here: https://mrmctavish.wordpress.com/2023/05/11/how-to-determine-belts-and-mechanisms-for-a-mechanism/
We did a two wheel shooter to shoot mini footballs using two 775 pro motors with 12:24 belt ratio and could shoot the balls the length of the gym.
Unfortunately, the only good way to get those values is through lots of prototyping. There are just too many variables in a wheeled shooter to be able to accurately calculate it.
For finding the flywheel speed, you can start with my projectile calculator to get the ball’s exit velocity from the shooter. Then you can figure that the surface speed of the flywheel will need to be some factor larger than that (because it’s likely that the wheel will still be slipping on the ball when it leaves the shooter). What that factor is depends on the particulars of your shooter setup; you’ll need to prototype to find it out.
As far as torque and how much power you need, the biggest thing that will change is your recovery time (i.e. how long it will take from the time you shoot one ball to the flywheel being at speed ready to shoot another). But again, this depends on a lot of other factors as well: system inertia, closed-loop tuning, viscous friction, etc. If you’re only shooting one ball at a time, recovery speed isn’t as important and you can probably get away with less power; if you’re shooting continuously, you need a lot of torque and power to keep up.
You do not want compliant wheels on a semi high speed shooter. They are not made for the forces involved,and change shape substantially.
Enough speed to to reach the reach the furthest shoot point with about like 30% headroom but no further. Shooters can be geared down if their free speed is excessive to have more torque to accelerate the flywheel, recover faster, and be easier to control.
In 2022, my team calculated that a 1:1 motors on a 4" main wheel and a 3/4 surface speed top wheel would be excessive so we put a 21:15 belt reduction on the shooter motors for even faster recovery time. We ended up only needed 4500 motor rpm even with the reduction to shoot from the very corner of the field. Whereas in games like 2020, very high surface speed was desired to shoot flat arcs from the trench, upductions around the 1:1.5 range were common.
What wheels do you recommend?
Most of the single piece molded wheels like stealth wheels work well. Higher cost options like WCPs urethane shooter wheels are out there but are overkill for most projects. Andymark highgrip have worked well for us too.
Compliant wheels also deform in inconsistent ways when they make contact with the ball, leading to undesirable variations in shots. Great for intakes, but not for shooters
I’ll second AM Stealth wheels, we’ve used the green (35A) ones for the past two shooter games and they work great. Note that the “best” wheel for any given game will vary depending on the type of game piece though, so Stealth wheels may not be the best option for every game.
To your original question, speeds and torque, it depends on the game piece and the distance you’re launching it. For example, in 2020 we had a game piece that was relatively light and could be legally launched from pretty far away on the field, so we opted to go with two Falcon 500s on a 1:2.5 gearing (increasing the flywheel top speed from 6000 to 15000rpm), we never used the max speed, but we designed it to basically shoot the balls in as close to a straight line as possible (no need to calculate trajectory if you can point and shoot) from as far back on the field as possible. Conversely, in 2022 we basically just scaled up out 2020 shooter but because the ball was heavier and didn’t have to shoot as far, we ran the dual Falcon 500 motors on a 1:1 ratio.
100% Concur. Use math to get close and then test. We put our shooters in front of this board with a 6" grid and then filmed them in slow-mo at various motor velocities to get precise measurements of exit angle and velocity (and if you put a stripe on the ball, a decent look at the amount of backspin).
How is the combine used in the testing/data collection?
Sorry John, i just realized you’re in Iowa.
We used andymark green compliants for our 2022 shooter abd had great results that felt really consistent. We were making a solid 85% of shots from even like 25 feet away and we believe most inconsistencies were caused by the intake and cargo feeding mechanisms.
Regardless of teams having seen good success from compliant wheels in the past, I would definitely recommend against putting them in high RPM applications. Andymark lists their RPM limit as 9000 RPM, but I would guess you will have non-trivial deformation of the wheel at that RPM and that would cause some inconsistencies in the shots. Definitely recommend checking the deformation with a slow motion camera if considering usage in the future, it might be acceptable at the RPM you need.
Generally speaking, a hard wheel(ex stealth wheels) is used when the game piece is compliant, and a compliant wheel(Pneumatic wheels were popular in 2013) is used when the game piece is firm.
Surprisingly quite importantly. 
During the pandemic years we were kicked out of our normal work space and a friend of the team lent us space in his barn so we could continue to exist. And the barn cats hid in the combine when robot go brrrrr.
The big caveat there is that compliant wheels can work spectacularly well on rigid gamepieces (2013 frisbees).
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