Shooter Help

[Bongle]

Hey folks

We have a shooter problem. Basically, we don't have enough friction on the balls as they go through the mechanism. Since F_f = u_k*F_n and we've tried everything we can to increase u_k (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)