Abstract
Robust mechanisms for slip resistance are an open challenge in legged locomotion. Animals such as goats show impressive ability to resist slippage on cliffs. It is not fully known what attributes in their body determine this ability. Studying the slip resistance dynamics of the goat may offer insight toward the biologically inspired design of robotic hooves. This article tests how the embodiment of the hoof contributes to solving the problem of slip resistance. We ran numerical simulations and experiments using a passive robotic goat hoof for different compliance levels of its three joints. We established that compliant yaw and pitch and stiff roll can increase the energy required to slide the hoof by $\approx \text{20}\%$ compared to the baseline (stiff hoof). Compliant roll and pitch allow the robotic hoof to adapt to the irregularities of the terrain. This produces an antilock braking system-like behavior of the robotic hoof for slip resistance. Therefore, the pastern and coffin joints have a substantial effect on the slip resistance of the robotic hoof, while the fetlock joint has the lowest contribution. These shed insights into how robotic hooves can be used to autonomously improve slip resistance.
Highlights
I N RECENT years, there has been a growing interest to understand how dynamics of a physical agent can be used to simplify the computations required to survive in a real environment [1]
We found that since the compliance of each joint in the hoof is a critical vector of morphological parameters determining the slip resistance of the hoof, having a compliant pitch and yaw and stiff roll can increase the energy required to slide the hoof by ≈ 20% compared to the energy of the stiff combination, and that the coffin and pastern joints have a significant contribution in the slip resistance, while that of the fetlock joint is minimal
Results of stage energy for Cβ against Cθ, Cβ against Cγ, and the 3-D plot of the stage energy across the compliance of the three joints demonstrate that, in general, higher compliance at the pitch (Cβ) leads to higher slip resistance. These results are corroborated by the single-sided comparisons (p < 0.05, Mann–Whitney U-test at 1% significance level with Kruskal–Wallis with Bonferroni correction). These results show that the combinations with the highest slip resistance that present up to ≈ 20% increase of energy by compared to the baseline have a compliant Cγ and a stiff roll (Cθ0)
Summary
I N RECENT years, there has been a growing interest to understand how dynamics of a physical agent can be used to simplify the computations required to survive in a real environment [1]. They studied the behavior of the muscles and tendons of the hindlimb for inclined, declined, and level running. They conclude that the ankle, knee, and hip generate energy for inclined running. The energy is mainly absorbed in the ankle and knee. The joint between the hoof and the ankle (fetlock joint) is mainly absorbing energy during decline, level, and inclined running [8]. This energy-absorbing behavior may have an important role in the remarkable climbing capabilities.
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