  Musical expressivity is an important aspect of musical performance for humans
as well as robotic musicians. We present a novel mechatronics-driven
implementation of Brushless Direct Current (BLDC) motors in a robotic marimba
player, named Shimon, designed to improve speed, dynamic range (loudness), and
ultimately perceived musical expressivity in comparison to state-of-the-art
robotic percussionist actuators. In an objective test of dynamic range, we find
that our implementation provides wider and more consistent dynamic range
response in comparison with solenoid-based robotic percussionists. Our
implementation also outperforms both solenoid and human marimba players in
striking speed. In a subjective listening test measuring musical expressivity,
our system performs significantly better than a solenoid-based system and is
statistically indistinguishable from human performers.
