FRC Team 7694 is looking for a weighted flywheel for shooter. Thinking of 2 lb., 4 in. diameter, hex opening preferred.
Found sites that have the wheels we would need but no flywheels yet.
Considering an exercise weight but wanted to see what other options there were.
Thanks.
Vendors like McMaster will sell discs of aluminum, steel, etc that can be purposes as flywheels. It would be up to the team to bore and broach them.
Alternatively, you can select shooting wheels with more mass so that your launcher itself serves as a flywheel. Or mount additional wheels in non-launching positions to add more rotational intertia to the system.
Yeah, we’ve used chunks of steel (turned down 3.5” dia x ~1 in 12L14 Steel disk works well). We didn’t even broach. We matched the OD of the hex we used (either thunderheads or regular) and matched the bolt pattern of the vex hex wheel hub. You get a better trade off of weight vs inertia if you pocket out the disk (that is have more mass on the outside).
you can buy a 3" iron caster wheel at Home Depot, or a larger one from an industrial supply place such as McMaster. The 4" caster with round 1/2" bore is under $20. And if you want to just add a sprocket or pulley to the wheel, you can buy iron caster wheels with bearings, up to 16" diameter, from McM.
Can you explain bore and broach? thanks.
So the bore is the shape and size of the center hole i.e. 1/2" round 1/2" Hex etc.
Broaching is a machining process to create those bores. You make a hole that’s very close to 1/2" in size and then you push the broach through the hole to create a pattern. It requires a press and lots of travel. Broaches are also very expensive. https://www.andymark.com/products/1-2-in-hex-broach?via=Z2lkOi8vYW5keW1hcmsvV29ya2FyZWE6Ok5hdmlnYXRpb246OlNlYXJjaFJlc3VsdHMvJTdCJTIyYnV0dG9uJTIyJTNBJTIyc2VhcmNoJTIyJTJDJTIycSUyMiUzQSUyMmJyb2FjaCUyMiUyQyUyMnV0ZjglMjIlM0ElMjIlRTIlOUMlOTMlMjIlN0Q
This is a 1/2" Hex broach AM sells
@Ryan_Dognaux Thrifty Flywheel?
Maybe not thrifty. A bronze flywheel made using 4" o.d. x 1.75" i.d. stock would weigh 12 lb and have 0.025 kg-m^2 moment of inertia. With a large enough lathe you could bore it out to 1.875" i.d., then fit the ends with 1/2" hex hubs like the ones that Vexpro and Andymark sell. You’d want to coat it with urethane or something similar, for good grip on the gamepiece during the few milliseconds they’d be in contact.
At 5500 RPM, the flywheel would store about 4500 Joules kinetic energy, and each gamepiece would exit the shooter at about 65 ft/sec, taking about 28 Joules with it. So flywheel energy would be momentarily depleted about 0.7% by each gamepiece shot, requiring your shooter motor to replace that by accelerating (torquing) the wheel back up to speed.
Alternatively, you could save the 12 pounds and about $170 in material (plus your fabrication time) that the flywheel costs by using a more powerful shooter motor, which would replace the kinetic energy lost in your shooter wheel by accelerating it between shots. The more torque your motor can deliver, the faster the lost energy gets replaced.
As an example, we prototyped a shooter using a MiniCIM and flywheel, then replaced the MiniCIM with a Falcon 500 and removed the flywheel. Result: better shot repeatability and less time required between shots, because the Falcon 500 delivers considerably more torque than the MiniCIM.
Your milage may vary. We’re ditching the flywheel.
Oh…was I supposed to ask why the OP wanted a flywheel? Sorry…
Thanks, that’s a great answer! 
Cheap option:. Andymark sells 1/2 inch hex steel gears that are pretty heavy.
Also, note that you don’t have to have the flywheel on the same shaft as your shooter wheels. You can have it on an axle that is connected to the shooter shaft by chain or belt, for example.
We prototyped our shooter with a 6" VexPro Traction Wheel and two CIMs (which will be Falcons in the real design). No flywheel necessary beyond the mass of the wheel itself.
Yeah. Two 6" colsons on one old minicim did good. A falcon or neo would do much better. Flywheels were awesome in 2017. Are they necessary now? Mmm
Depends on how fast you want to shoot and from what distance. Shooting fast from up close is pretty easy, from a distance gets hard quick.
What kind of range were you getting with both setups?
Range depended a great deal on getting the compression right, but the answer to your question* is that we were maintaining a sweet spot from about ten to about forty feet.
*we only had the one setup
Well that narrows it down, I thought you were shooting from somewhere that wasn’t the field.
Full Disclosure: I have no experience with this product.
McMaster sells a steel wheel that is 4" diameter with a 1/2" round bore. I have no idea what it weighs, but because most of the material is at the rim, you will get the most inertia for the mass. You could broach the bore to 1/2" hex (although with steel, broaching will be less fun that it would be with aluminum) or there may be enough material in the hub to be able to bore it out to a larger diameter and then press in a hex hub or adapter of some sort.
With any modification to a wheel that you are going to spin at a high speed, you need to be capable to do this with a good level of control over the concentricity of the bore so that you can avoid vibration. I would recommend a lathe.
Thanks for posting this. It is very likely to be a better-cost flywheel alternative than the example I gave earlier. However, either one requires some accurate machining capability to avoid excessive unbalanced loading. A vibrating shooter will not give repeatable results, and will wear out components quickly. That is the main challenge inherent in the “thrifty flywheel” request.
I agree. Unbalance at high RPM is actually quite scary.And it is not just the rotational axis being offset, but also if the rotational axis is not perpendicular to the principle inertial axis. Wobble is just as scary as runout.
I actually hesitated posting that link as I am worried that a team without good machining capability might take this idea and try to modify this wheel using inadequate tools and tolerance control. Hopefully everyone observes these cautions if they are thinking of alter these wheels or any wheels that will be spinning at high RPM.