Solo project
The actuator transmission for the Six-DOF arm. Development started with a standard single-stage cycloidal gearbox, then branched into a custom three-ring cycloidal drive (inspired by Mishin Machine) chasing extremely backdrivable, low-backlash motion. This project tracks both lines of work and the iterations behind them.
Project Summary
A short look at the build, the main technical choices, and the pieces I iterated along the way.
The gearboxes are the actuator transmission for the Six-DOF arm. I started with a standard single-stage cycloidal drive, got it running and load-tested, then branched into an experimental three-ring cycloidal drive to chase better backdrivability.
A working 20:1 standard cycloidal actuator, and a five-revision three-ring cycloidal drive prototyped from hand-crank rigs up through motorized load tests.
The standard drive stalls at 50 percent of theoretical capacity for a 20:1 ratio on a NEMA 17. The three-ring line surfaced slipping plates and inner-pin bending, and after fixes still showed low torque efficiency, so the production actuator went back to the standard layout.
Drives
The current gearbox in progress is the innie cycloidal drive, shown first. Everything below it is past iteration work that led here — the earlier outie cycloidal, then the experimental three-ring cycloidal drive.
The current gearbox in progress. A single-stage 20:1 cycloidal actuator driven by a NEMA 17, redesigned with the output rollers pulled inside the housing for a more compact, better-supported drive than the earlier outie layout.
The current innie cycloidal design, with the output rollers pulled inboard between the plates and the output crank arm on the front.
The assembled innie drive with the cap off, showing the ring of inboard rollers and the output arm seated on them.
Everything below is earlier gearbox work that led to the current innie drive — the designs it replaced, kept here as the iteration history. First the outie cycloidal it grew out of, then the experimental three-ring cycloidal drive.
The earlier cycloidal layout, with the output link and square drive socket. This is the design the innie cycloidal replaced.
The earlier outie layout, with the output link and square drive socket.
A custom three-ring cycloidal drive inspired by Mishin Machine, aimed at extremely backdrivable, low-backlash motion. Five hardware revisions, each hand-cranked before motorizing to check smoothness before load testing.
First three-ring concept in Onshape, set up as a hand-cranked rig to feel out smoothness and backdrivability before motorizing.
Swapped in metal pins to survive load, still hand-cranked for evaluation.
Stacked plates slipped against each other under load, making torque measurements unreliable.
First motorized test surfaced inner-pin bending under torque.
The fully assembled v4 three-ring drive.
Hand-cranking the v4 drive with no output arm attached to check smoothness and backdrivability.
The motorized v4 hardware with the output arm attached, showing the smooth, highly backdrivable motion the three-ring layout was chasing.
The stacked plates shifted relative to each other under torque, degrading the transmission.
Under load the pins slipped, one of the failure modes that showed up once v4 was driven by the motor.
After all fixes the drive still showed low torque efficiency, so I switched the production actuator back to the innie cycloidal layout.