Meeting Abstract
Animal legs are diverse, complex and perform many roles. One defining requirement of legs is to facilitate terrestrial travel with some degree of economy. This could, theoretically, be achieved without loss of mechanical energy if the body could take a continuous horizontal path supported by vertical forces only – effectively a wheel-like translation, and a condition closely approximated by walking tortoises. If this is a potential strategy for zero mechanical work cost among quadrupeds, how might the structure, posture and diversity of both sprawled and parasagittal legs be interpreted? In order to approach this question, various linkages described during the industrial revolution are considered. Watt’s linkage provides an analogue for sprawled vertebrates that use diagonal limb support, and shows how vertical-axis joints could enable approximately straight-line horizontal translation while demanding minimal power. An additional vertical-axis joint per leg results in the pull-out screen support as an analogue for tortoise limbs. This allows walking without any tipping or toppling, and has the potential to translate the body with zero work. The Peaucellier linkage demonstrates that parasagittal limbs with lateral-axis joints could also achieve the zero-work strategy. Suitably tuned four-bar linkages indicate this is feasibly approximated for flexed, biologically realistic limbs.
