Rolling friction of a rugby wheelchair

The rolling friction coefficient is treated either as a constant, or a constant plus a parabolic velocity-dependent component. According to mathematical models, the rolling friction coefficient of visco-elastic objects increases first and drops at higher speeds. The aim of this paper was to analyse the non-linear rolling friction of a rugby wheelchair as a function of speed. Nonlinear velocity-dependent drag and lift coefficients were determined in the wind tunnel. In order to obtain the friction coefficient, we applied the coast down method on three different floors (wood, linoleum, and short-pile carpet) by instrumenting the wheelchair with an accelerometer. The rolling friction coefficient was calculated from the ratio of the difference between inertial force and drag force to the difference between weight and upward lift force (where all forces are absolute values). The friction coefficient µ of the carpet floor was the highest (µ=0.0143; mean weighted to velocity), followed by the linoleum floor (µ=0.0061) and the wooden one (µ=0.0042). µ of carpet and linoleum showed no clear trend in the velocity range of 0¿4 m s-1 and can be treated as a constant. µ of the wooden gym floor increased, then dropped and increased again with speed. A fit function based on a combined Bateman and parabolic function was applied to the wood data in order to separate the initial peak from the velocity dependency at higher speeds.