Interaction Mechanics Model for Rigid Driving Wheels of Planetary Rovers Moving on Sandy Terrain with Consideration of Multiple Physical Effects

Abstract

Predicting wheel‐terrain interaction with semiempirical models is of substantial importance for developing planetary wheeled mobile robots (rovers). Primarily geared toward the design of manned terrestrial vehicles, conventional terramechanics models do not provide the sufficient fidelity required for application on autonomous planetary rovers. To develop a high‐fidelity interaction mechanics model, in this study the physical effects of wheel lug, slip sinkage, wheel dimension, and load are analyzed based on experimental results, including wheel sinkage, drawbar pull, normal force, and moment, which are measured on a single‐wheel test bed. The mechanism of lug‐terrain interaction is investigated systematically to clarify the principle of increasing shear stress, conditions of forming successive shearing among adjacent lugs, and the influence on shear displacement of soil. A mathematical model for predicting the concentrated forces and torque of rigid wheels with lugs for planetary rovers moving on sandy terrain is derived by integrating the improved models of normal and shearing stress distributions. In addition to the wheel parameters, terrain parameters, and motion state variables, wheel‐terrain interaction parameters, such as the linear varying sinkage exponent, the soil displacement radius, and load effect parameters, were proposed and explicitly included in the model. In the single‐wheel experiments, the slip ratio was increased approximately from 0.05 to 0.6, and the relative errors of the predicted results using the proposed model are less than 10% for all the wheels when compared with the experimental data. The proposed model has been used in the simulation of a four‐wheeled rover, and its effectiveness is evaluated by comparing the simulation results with experimental results.

Improved explicit-form equations for estimating dynamic wheel sinkage and compaction resistance on deformable terrain

“…In order to reflect the wheel lug effect on the shear stress, the shearing deformation is improved [5]: where…”

“…The wheel sinkage was measured directly by the displacement sensors. The compaction resistance cannot be measured directly, but it was estimated by a high-accuracy integral terramechanics model that considers the effect of wheel lugs, slip sinkage, and load effect with errors of less than 10% [5], using the parameters (as shown in Table 5) identified according to the experimental results of different wheels moving on soil HIT-LSS1. Notice that the parameters in Table 5 were identified based on wheel-terrain interaction mechanics model, so that they are not the same as those in Table 2.…”

“…Estimate the normal and shear stress distributions based on the integral-form model considering multiple effects [5]. Calculate the integral compaction resistance and λ FNτ as a function of the slip ratio s. (2) Modulate n 0 and n 1 to estimate the wheel sinkage z by trial and error using Eq.…”

“…Irani et al observed the fluctuation of wheel-terrain interaction due to lugs and deduced a dynamic model for light-weight vehicles' wheel moving on sandy terrain [25]. Ding et al deduced a comprehensive model [5] that reflects the slip sinkage [26], lug effect, load effect, and dimension effect for planetary exploration WMRs. Ishigami et al deduced lateral force equations for steering maneuver of planetary rovers on the basis of the Wong-Reece model [21].…”

“…However, the wheel sinkage is in turn influenced by the shearing stress that determines the driving torque. Therefore, an iterative process [5] is required while calculating the wheel sinkage, slip ratio and driving torque given the normal load and drawbar pull. Wheel sinkage (m) e z…”