Octocanum 101

[Paul Copioli]

All,

Just to stop the speculating on this one, we know exactly what is happening because of all the great feedback we have received from our customers via our support e-mail channel.

This failure mode has almost nothing to do with the transmitted torque to the wheel. The way these wheels are designed to eliminate the "mecanum bounce" flexes each individual roller from tip to opposite tip. This deflection causes cyclical stress across the roller hub. We have a stress concentration at the base of the roller boss (where the shaft bushing is located) that sees a fatigue stress at around 4 hours of driving time for the 4" mecanum.

This failure is caused by two things:

1. Our resin manufacturer did not use the specified brand of resin for the injection molding pellets. They used the correct material, but a brand that had a lower fatigue strength.

2. Our hub design had a stress concentration at the exact wrong location on the rib. This stress concentration was due to too small of a fillet on the roller boss.


We have redesigned the roller hub and put in process checks in place to guarantee the correct material in production. We are currently modifying the injection mold for the roller hubs (the 6", 8" and 4" all use the same hubs, just different rollers).

With all of that said, this problem should only show itself on your extended hour practice robots. Competition robots will need to participate in approximately 96 matches (including practice matches) to equal 4 hours of run time. We have reduced the price of the replacement roller kits to below our cost in order to temporarily assist teams while we await the improved roller assemblies.

My plan is to send the new roller kits to all customers of the 4" mecanum wheels free of charge once they are in stock.

I hope this was helpful in understanding the problem.

Paul