Towards a Comparative Measure of Legged Agility

We introduce an agility measure enabling the comparison of two very di↵erent leaping-from-rest transitions by two comparably powered but morphologically di↵erent legged robots. We use the measure to show that a flexible spine outperforms a rigid back in the leapingfrom-rest task. The agility measure also sheds light on the source of this benefit: core actuation through a su ciently powerful parallel elastic actuated spine outperforms a similar power budget applied either only to preload the spine or only to actuate the spine during the leap, as well as a rigid backed configuration of the identical machine.