A team of scientists from the Center for Interdisciplinary Studies in Rhythm, Time, and Motion at the University of Oslo has developed a drum robot named ZRob. This robot features a flexible “wrist” that can hold drumsticks loosely, similar to a human wrist. The robot drummer can listen to itself while playing and uses reinforcement learning (RL) to improve its performance.
ZRob is not particularly large. It mainly consists of a 3D-printed case housing a 48-volt DC motor that drives an arm with two degrees of freedom. Attached to this arm is a flexible holder for a drumstick, suspended on two springs. This setup gives the robot arm the flexibility needed for playing drums, akin to a human wrist. The study “Embodied intelligence for drumming; a reinforcement learning approach to drumming robots,” published in Frontiers in Robotics and AI, outlines these details.
The researchers point out that humans often use their bodies to add expression to their musical instrument playing. They aim to achieve something similar with ZRob. By giving the robot a flexible drumstick holder, it becomes more adaptable. Changing the springs to ones with different stiffness can influence the drumming style and sound, effectively making the robot’s body contribute to its playing behavior.
ZRob is controlled at the lowest level by an Arduino microcomputer. It is provided with MIDI data that outlines the basic drumming patterns. To optimize the robot’s performance, the researchers employ reinforcement learning. Acoustic information from the drumming is captured via a microphone, and the artificial intelligence (AI) is trained using RL to enhance the drumming.
The RL algorithm is based on the Deep Deterministic Policy Gradient (DDPG) method. The robot is trained with a combination of intrinsic and extrinsic rewards, rather than relying solely on extrinsic rewards. Intrinsic rewards can lead to the creation of new rhythmic patterns, while extrinsic rewards result in predictable patterns that match the MIDI data.
However, the scientists do not believe that this type of robot music can touch people in the same way as human-made music. ZRob can create new types of rhythms and play drums much faster than a human. Currently, multiple ZRobs are needed to play a full drum set.