Modifications to FIRST Gray Wheels for Better Consistency

[Cal578]

Originally Posted by HumblePie

...We later replaced the spacers with a 6 inch diameter flywheel to increase the inertial mass, which seemed to yield some additional consistency. ...

Did you test anything before and after adding the flywheel, to determine how much improvement it provided?

I'm very interested in flywheels and how much benefit they provide. I started a thread on it:
Flywheels and Shooter Wheels

To answer the OP's question, the only special thing we do is clean our shooter wheels with alcohol pads between matches.

[beiju]

We have a surprisingly precise shooting system, even at high power, and I think our secret is our conduit guides. Most teams I've seen have either two sets of rotating wheels, which is inherently inaccurate because of the difficulty of syncing two motors, or a flat hood to guide the ball on the top. Rather than one hood, we have two pieces of conduit that roughly follow the curve of the wheels spaced between 3 and 4 inches apart. We have two shooting wheels on the same axle, between 2 and 3 inches apart, and the combination of those keeps the ball exiting the shooter very consistently.

Another thing we were careful about is avoiding any interference on the ball near the top of the shooter. The conduit is attached securely at the bottom so we don't need any attachments at the top that might contact the ball inconsistently and so throw off its trajectory.

Other specs:
-$@#2" squish factor
- 6" traction wheels, covered with duct tape because we were shredding balls
- 5000 rpm and ~150 oz-in of torque on the shooter (the torque is on the low side of what we would like)
- consistent feeding from a belt

[thefro526]

A few tricks that I've picked up with the help of some friends:

1) Turn the 'Crowns' off of the wheels. If you look at a fresh FIRST wheel, the tread isn't flat but actually 'U' Shaped. I turned the crown down by putting the wheel in a lathe and taking a file to it.

2) Make sure the balls are entering the shooter consistently. Some systems I've seen have allowed the ball to move around left to right before hitting the shooter wheels. In a perfect world, the ball enters on the same center as your shooter wheels 100% of the time.

As far as compression goes, it's really dependent on your style of shooter.

[CalTran]

Our team, in between competitions, simply fabircated our own custom 9" wheels out of 1" thick aluminum stock. All the weight is now on the edge, and they have a custom chamfer now. Those turned out really nice We love them now.
However, before we did this, we were using the 8" rubber tread wheels from the KOP a few years ago. What we did to somewhat improve consistancy was chamfering them, albeit rather crudely. The quickest way to chamfer them would probably be just spin them up and hold a file to them. (And cover anything below them! )

[philso]

Originally Posted by thefro526

2) Make sure the balls are entering the shooter consistently. Some systems I've seen have allowed the ball to move around left to right before hitting the shooter wheels. In a perfect world, the ball enters on the same center as your shooter wheels 100% of the time.

We padded the side walls on either side of the ball from before it gets fed into the shooter all the way out. We originally had about 3/8 inch on either side.

Our original "hood" was a 1 1/2 inch wide piece of hardwood cut on a bandsaw to get the required curve. At Alamo, we discovered that the cut was not perpendicular to the wood, causing a tilt to one side when the ball was launched. We were able to straighten it out with several layers of duct tape on one side. Our new hood is adjustable for tilt, compression and curvature.

We may have had some inconsistency when the wheels were not rigidly attached to the shaft. We are using two of the 8 inch gray wheels on AndyMark hubs and a 1/2 inch smooth (no keyway) shaft. We drilled and tapped the hubs for two set screws each. We also drilled into the shaft, through the set screw holes, so that the sets screws have more "bite". Sometimes the set screws loosen and the wheels will wobble on the shaft even though they do not spin.

Using an encoder to enforce a constant speed on the wheel will help, if you are not already doing so. Also, allow time for the wheel to come back up to speed. I have seen several instances where one of the top teams fires off several shots in rapid succession and the later ones all fall short, by more and more.

Probably the most important thing is to make sure your test method is consistent. We were able to see variations in the trajectory of the ball as it left the shooter by holding up a yardstick and comparing the trajectories of a series of shots.