We have a shooter problem. Basically, we don’t have enough friction on the balls as they go through the mechanism. Since F[sub]f[/sub] = u[sub]k[/sub]*F[sub]n[/sub] and we’ve tried everything we can to increase u[sub]k[/sub] (even double-sided tape won’t get us enough grip on the balls), we need to increase the normal force by squeezing the balls more. However, this is a large problem because we built the spinning wheels of our shooter too far apart. We can’t move the actual spinning wheels closer together, since they are driven by a single motor, and the power transfer from one side to another is done by a horizontal shaft. We cannot easily shorten the shaft at the competition, as it would mean basically re-sizing the entire shooter assembly.
We have decided we need to somehow legally increase the radius of the skyway wheels so that they crush the balls more as the balls pass through. However, simply wrapping things like entire rolls of duct tape around the wheels is out, as duct tape is adhesive and therefore against the rules. I thought of saran wrap, but it would be difficult to apply and keep on. The current competition plan is to just put weather stripping around the wheels to again try and increase the coefficient of friction, but we don’t have high hopes. Can anyone think of a clever, legal way to make our shooter better?
Replacing the wheels with slightly larger wheels is a distant possibility (taking the wheel axles out is nearly as difficult as shortening the shaft)
Replace the wheel on one side with a fixed post. Your balls will have an interesting side spin, but they will shoot. Try for about one inch of compression. I’m guessing that you won’t find anything that will make your Skyways bigger. I guess that you could replace one of the Skyways with a wheel that is one inch larger, but that could be really complicated.
Come visit our pits on Thursday of the GTR. I’ve got some ideas that could alleviate your problems. We’re always willing to help a team, especially one that we won a regional with.
If you go with attaching conveyor material on wheels spinning 2500 rpm you want to make sure it is attached REALLY well, and that it is evenly spaced around the perimeter. You run a real risk of hurling conveyor material around the arena at 25 MPH, or having your mechanism shake itself apart from vibration. I would think long and hard before attempting this – it’s not like riveting conveyor material onto wheels spinning at a few hundred RPM.
The belting is your best bet. I would go with rough top, or a smoother finish, rather than wedge. Bring really good contact glue and small screws and a belt sander. Run the shooter at a reasonable speed use the belt sander (80 grit or so) to get the wheels closer to flat, glue and screw the belting on and you should get both, better grip and a larger wheel. Normal procedure to make the wheels flat is a metal lathe, we have done it that way I’ve never been present. I did try a router once…Not a good idea. The carpet on the skyway wheels last year did a nice job on our non belted wheels that’s why the sanding suggestion. BTW your wheels should be spinning about 1200 give or take a little 2400 would be the case if you were only driving one side and a had a non moving side.
These are all good ideas guys, thank you very much.
I thought of another one while talking to a teammate: a thick car timing belt as a rigid backing to weather stripping. The timing belt would increase the radius, while the weather stripping would increase the coefficient of friction. A long-enough timing belt would be wrappable around the wheel multiple times, and any little bumps would be smoothed over by the weather stripping layer. Any thoughts?
you could also move the pairs of wheels closer to the centerline of the ball, or replace each pair with a single wheel. since the ball is wider in the center the wheels would contact it at its widest point, without having to increase the wheel size, or bring them closer together horizontally.
