Team 100’s 2020 FRC shooter uses 60A durometer 4" Fairlane neoprene (chloroprene) rubber wheels, McMaster-Carr part number 2476K37. There is a question whether the wheels can be spun at the speeds necessary to launch power cells (foam balls) in the Infinite Recharge game without over-stressing the wheels. Accordingly, we have performed a axisymmetric stress analysis to calculate the radial and hoop stresses and the radial displacements in the rubber and steel.
The analysis shows that radial stresses in the rubber are highest at the interface with the steel core, and are maximum 300 psi at 9,500 RPM as compared to a tensile strength at break of >1723 psi for the chloroprene referenced in the paper. At 9,500 RPM, radial strains in the rubber at the interface are 27% as compared to an elongation at break of >287%. Hoop stresses in the steel are maximum 4,000 psi at 9,500 RPM as compared to 36,000 psi for garden-variety ASTM A36 steel. The wheel is expected to expand <0.25" at 9,500 RPM.
This analysis does not at all support the wrapping the specific 60A-Durometer Fairlane rollers with stainless steel “safety” wire. The analysis indicates that stresses, strains, and displacements would not exceed values that the rubber would be expected to withstand, with considerable margin, provided the mechanism providing the rotation itself was robust and maximum speed was controlled.
This analysis carries certain limitations. It assumes that Seals Eastern neoprene parameters are applicable to Fairlance 60A rollers. We would not expect significant differences if we had the actual Fairlane neoprene properties. This analysis also assumes that the rollers are free of defects, including manufacturing defects or holes drilled for “safety” wires. This analysis is only applicable to the specific geometry, materials, and use conditions modeled. Any use of this analysis is at the user’s sole risk.