A stiffer grip, the first pulled double, and three agents in one 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.
The robot plays its doubles from the rebound: the finger motor renders a spring at the grip, and the stiffer that spring, the sooner the stick comes back for the second note. Until this week the firmware capped the spring’s stiffness at 4 N·m/rad, which set a ceiling on how fast a double could go.
A stiffer grip
The cap had never been tested as a stability limit. This week it was. At the bench the rendered spring stayed stable across the whole range from 4 to 16 N·m/rad with no ringing, and a double-stroke exercise on both hands played clean at 260 BPM in three runs out of three and at 280 in two out of three. The limit turned out to be the singles, not the doubles. The ceiling is now 16.
Pulling the slow ones
The opposite end had a gap too. The softest spring the grip can render without the stick sagging under gravity bounces back in about 115 ms on the right hand and 140 on the left, by this week’s measured calibration, so any double slower than that landed early. A drummer playing slow doubles doesn’t wait for the rebound; they lift the stick and drop it for the second note. The robot now does the same: after note one the grip holds the stick in line, and the wrist lifts it to the written height and brings it down on the beat. The first pulled double on hardware was written 125.0 ms apart and landed 123.6 ms apart.
Not there yet
That roll’s 4.5 ms is just outside the robot’s timing target of 4.3 ms, the best measured among 29 human players. And nobody has yet compared these doubles with a drummer’s by ear; the loudness of the second note against the first is the next measurement.