When a drummer plays a fast double stroke, the wrist throws the stick once, the stick bounces off the head, and the fingers bring it back down for the second note. My robot does the same. A motor at each grip acts as a spring, and the spring's stiffness sets how soon the second note comes back.
A double-stroke exercise at 260 BPM on both hands: 49 of 49 notes, onset scatter 3.3 ms. Recorded at the bench on 5 October 2026.
I'm Christopher Culbreath, and I loved marching band. I played snare, I met my wife in band, and my car's license plate read YA BAND. I was well known as the biggest band nerd at my high school, and I pictured my future as a high school band director. Twenty-five years, three kids and a PhD later, I'm building a robot drumline.
It starts with the snare. The goal is a robot that sounds like a person playing it.
Two salvaged hoverboard motors swing the sticks. A small gimbal motor at each stick's pivot holds it the way a hand would, as a spring the controller can make stiffer or softer for every stroke. A Teensy 4.1 runs the stroke controller, and a simulation built from bench measurements plays every piece before the robot does.
While Claude has written most of the code, I've developed a hardware-in-the-loop, self-documenting harness that makes agentic hardware development work. Every powered move is stated and confirmed before it runs, a digital twin plays each change before the robot does, every result is filed to a record, and an agent reconciles that record every night.
The grip spring's ceiling went from 4 to 16, slow doubles learned to be pulled, and the robot's first takes on the merged firmware played 49 of 49 notes.