An arm suspension mechanism for an underactuated single legged hopping robot

The geometry, kinematics, and mechanical development of a symmetric and adjustable arm suspension mechanism for an actively stabilized single-legged hopping robot are presented. This mechanism is a key enabling design feature of a recently developed two-armed reaction wheel stabilized monopod, that is capable of conventional wheeled roving, continuous hopping, and self-uprighting. The mechanism is shown to behave essentially as a digressive-rate torsional spring placed between the two arms, in series with a weaker progressive rate torsional spring tied to the leg/central body. This makes it well-suited to recovering substantial energy from hopping motion, whilst presenting negligible resistance to antisymmetric motions used to maintain side-to-side stability. Furthermore, by storing energy purely in tension, the problem of buckling encountered with compression springs is avoided, and, the effective torsional spring constant may be varied by adjusting the spring pretension. Finally, the mechanism is self-latching near maximum deflection, allowing the vehicle to fold into a compact roving configuration, and enabling "running jumps" via the release of this gradually accumulated spring energy.