Drum roll: increasing bandwidth through passive impedance modulation

Skilled drummers can play drum rolls at frequencies well in excess of human motor control bandwidths, by allowing the drumstick to bounce passively against the drum head at least twice for each hand stroke. We present experimental evidence that drummers modulate grasp force to control the effective stiffness of the drumstick which in turn determines the bounce frequency. To confirm this explanation, we constructed a simple, single-joint robot that emulates the human drumming technique. McKibben "artificial muscle" pneumatic actuators were paired in an agonist-antagonist configuration, resulting in a slow robot with variable passive impedance. The robot can execute drum rolls across a frequency range comparable to human drumming (bounce interval=40-160 ms). The results demonstrate that modulation of passive impedance can permit a low bandwidth robot to execute certain types of fast manipulation tasks.