Abstract: The paper presents an inchworm robotic insect that is capable of motion over smooth terrain. The structure is lightly-damped and consists of a unimorph piezoelectric actuator (THUNDER) that acts as both structural member and source of motion and two custom-designed limbs that are attached to the body by means of adjustable clamps. The limbs can either roll or drag on the ground when an appropriate resonance is excited. The approach is called elastodynamic locomotion. A cycle of this `falling-ahead' unidirectional motion is composed of two segments: a shorter one when the front leg is rolling on the ground surface and transports the structure ahead while the rear leg drags on the ground, and a longer one, when the legs interchange their functions. The mathematical model assumes the legs are compliant. The geometry of deformation was utilized to find a configuration that is capable of maximizing the horizontal displacement of the robot. An actual inchworm design produced a motion that confirmed the theoretical predictions. A lumped-parameter dynamic model was formulated that allowed evaluation of the ground reaction forces and the velocity of the robot by using data of the geometric model and solving the inverse dynamics problem.!12
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