A grouser spacing equation for determining appropriate geometry of planetary rover wheels

Grousers, sometimes called lugs, are recognized as a way to improve wheel performance and traction, but there have been, to date, no comprehensive guidelines for choosing grouser patterns. This work presents a quantitative expression for determining appropriate grouser spacing for rigid wheels. Past empirical studies have shown that increasing grouser height and number can improve performance, to a point. The newly proposed grouser spacing equation is based on observations that wheels with an inadequate number of grousers induce forward soil flow ahead of the wheel, and thus rolling resistance. The equation relates geometric wheel parameters (wheel radius, grouser height and spacing) and operating parameters (slip and sinkage), and predicts a maximum allowable grouser spacing (or, equivalently, a minimum number of grousers). Experiments with various grouser heights and numbers demonstrate good correspondence to the proposed equation, as increases in number of grousers beyond the predicted minimum number stop improving performance. A grouser spacing equation is particularly useful for designing efficient wheels. The proposed relation includes slip and sinkage, parameters that cannot be assumed constant or known a priori, but this work shows that wheels designed using the proposed equation are robust to changing operating scenarios even if they degrade beyond estimated nominal conditions.