Shooter wheel balancing

So we noticed (but pretended not to) that our shooter wheel had a little vibration in it during testing right before shipping. Does anyone have any clever ideas on how to balance it? Obviously we would want to remove a little material from the heavy side (it’s an 8" plastic wheel with rubber tread). I was thinking of spinning it a few times by hand and waiting to see which side ends up at the bottom. The problem with this is that the axel bearings are a little stiff, so this method may not be too reliable. Any cool ideas out there? I’m hoping to have time to fix it during our Lonestar Regional, you know how much free time there is! Or maybe we should just call it our ball agitator/shooter :smiley:

One way to do it would be set up to beams about 4" apart parallel to each other. Then put an axel through your wheel and set the two sides of the axel on the beams with the wheel in the middle. Look for the side that falls to bottom, and START FILING :smiley:

Mike C.

It only has to last about three minutes. I wouldn’t worry about it, unless the vibation threatens your structure.

I agree, but it all depends on the amount of vibration. If you feel that it’s excessive then go ahead and try to fix it. But I wouldn’t worry too much about it. There could be any number of things that are throwing it out of balance as so it might not just be the wheels (of coarse I’m thinking of a shooter with a drive train, but who would do that :rolleyes: ).

Again, it all depends on where you mounted your vibration sensitive parts. Our wheel shook like there was no tomorrow. (maybe not as bad a s yours, but still pretty strongly) We fixed it, sort of. For us it was more of a aesthetics issue than a functionality problem. So, anyway, we got rid of the turreting action (for other reasons) and tightened some bolts. Now, instead of only having to shake itself, some 80/20, and sheet metal while mounted on a single turntable bearing, it had to shake the whole robot. It really couldn’t overcome the inertia of the bot to produce meaningful shaking. Even if it did, it wouldn’t have mattered much since all our electricals were mounted to Plexiglas which would absorb vibrations.

Our vibration isn’t all that bad. As an ex-Navy mechanic, though, it sort of offends me :slight_smile: I’m pretty sure the vibration is coming from the wheel, the shaft is good-n-straight with nice sturdy block bearings on either side of the wheel coupled via spider coupling to the motor. It really is sort of a low priorty fix right now, we need to complete some more important things first (like our ball feed). Just in case I have a kid standing around, though, I can have him work on it.

One way to do it would be set up to beams about 4" apart parallel to each other. Then put an axel through your wheel and set the two sides of the axel on the beams with the wheel in the middle. Look for the side that falls to bottom, and START FILING

I think this idea should work :slight_smile: I was hoping for something to do in place though.

Be sure to not completely ignore off balance wheels. Our wheel had part of the tread come off; the then massively off balance wheel rotating at 4000 rpm broke our rotator (this was during build).

If you’re not going that fast, you shouldn’t have to worry much though.

Static and dynamic balance will be different. You may be better off with trial & error. Try a light weight in different spots around the wheel and see if it gets better. If it gets better, try more or less weight.

Excellent idea, at least we can try it in situ and see if it works. How to attach small weights, though? Perhaps small screws in the side of the wheel?

I’m sure the wheels are held at the manufacturing plant for them to some sort of trueness, but the higher RPM they spin the more you notice imperfections.

The wheels you are talking about were probably designed to go way slower than you are spinning them. How many wheelchairs do you know that have the front wheels spinning 20+mph? lol

Anyways, keeping that in mind, check your pillow block or whatever you are affixing it to your frame to. Make sure they are aligned right. One .050" difference in center lines of the block from the X axis will make your wheel wobble a heck of a lot at these high speeds.

Yes as you said the wheel we are using is normally a drive wheel (from NPC robotics), but they aren’t made for the speeds we are using them at! I used a dial indicator to check alignment on the wheel and motor shaft and it was pretty good. But, it is quite possible that it has gone out of true since then. We use VERY high tolerance engineering (i.e. 1" ± .25") :smiley: Maybe we should harness the vibration as a battery charging mechanism!

That’s exactly what we did, except we sent it out to be balanced in a shop with specific equipment. They balance car and truck tires so a request to dynamic balance a small tire at 1500 RPM sounded a bit weird to them. Only cost $20 dollars, though. With guarantee (one of the tires was out of balance after a while so they redid it)!!
I think the machine uses lasers to detect the tire wobble, but I’m not sure. Anyway, it’s a fancy machine.

That’s probably not a solution now that your robot is gone, but you can try the low tech method described above. It won’t be perfect, though, since you probably won’t be able to balance it up to the high rotation speed we normally use in FIRST shooters.

Ours were balanced professionaly. They are high speed gocart wheels.

I wanted to add some observation here. After two weeks of inspections, the teams that had problems with vibration were using small wheels designed for a much slower speed. As they brought them up to get near to the 12M/s speed rule, they would vibrate. Typically this was the 4" diameter vs. 6" diameter wheel chair type wheels.

Sounds about right. Our’s is 8" so at least we don’t have to spin it TOO fast, although we are estimating 1200 rpm. Still faster than it was really designed for. Maybe the magical crate fairy will fix it for us! We will find out tomorrow!

Isn’t that the fairy that turns the crate upside down and drops it off the truck?