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

Abstract

Abstract-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.

Visualizing and Analyzing Machine‐soil Interactions using Computer Vision

“…Studying grousers has identified the strongly periodic effects they induce in soil. SOFT has engendered the discovery of periodic resistive forward flow (Moreland et al., ), leading to the development of a quantitative equation for predicting appropriate grouser spacing (Skonieczny et al., ). Other ongoing experimental campaigns include studying the effects of varying slip in different soil types, of varying wheel diameter, and of varying normal load on the wheel.…”

“…It has been used to study how soil failure under wheels is modified when implementing a novel inching locomotion mode (Moreland et al., ). It has also been used to study the effects of grousers on wheel traction (Moreland et al., ; Skonieczny et al., ). This work develops SOFT in detail and characterizes its performance quantitatively.…”

High‐speed mobility on planetary surfaces: A technical review

“…The increased contact area of these wheels improves traction and increases the level of compliance when overcoming obstacles and jagged surfaces. Even though the benefits of grousers have been extensively analyzed (Inotsume, Skonieczny, & Wettergreen, ; Moreland, Skonieczny, Inotsume, & Wettergreen, ; Skonieczny, Moreland, & Wettergreen, ; Sutoh, Nagaoka, Nagatani, & Yoshida, ) and their influence in the augmentation of traction levels has been modeled (Jia, Peng, & Smith, ), this extension to the classical equations is also frequently ignored for simplification. The same applies to the modeling of flexible metallic wheels (Favaedi, Pechev, Scharringhausen, & Richter, ).…”

Design optimization of a lightweight rocker–bogie rover for ocean worlds applications

“…Varying the geometry of grousers has a substantial effect on the contact mechanics when interacting with granular and hardened terrains. Prior research 52 developed a grouser spacing equation through experimental studies in loose granular soil. Here, it was identified that a small number of grousers could introduce resistive flows of loose soil, reducing tractive efficiency.…”