The interlock drive system generates traction by penetrating articulated spikes into the ground and by using the natural strength of the ground for traction. A fundamental problem of traction by interlocking spikes is how to penetrate the ground such that the spike will withstand the draft force. The theory of critical depth suggests that a high rake angle reduces soil fragmentation, while vehicle stability and demand for a high pull/weight ratio require a low thrust angle. To satisfy both requirements, we connect an interlocking spike with a high rake angle via a lever arm to a hinge close to the ground for a low thrust angle. The resulting friction of the spike with the soil increases the vertical penetration force during penetration. Experimental data shows that such a spike penetrates soil of a much higher penetration resistance than predicted from an analysis of the forces involved, possibly because the spike follows the path of least resistance. To better understand and improve the potential of interlocking spikes for mobility in extreme terrain, we need a comprehensive experimental analysis.
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