Overhead view of the assembled quadruped showing the computer, wiring and servos packed inside the body

RoboticsPart 1 of 2Drawing 3.1 of 37

The machine

Twelve joints on a printed chassis, with the knees driven through pushrods. Emin Alp Arslan and I designed and built it across 2021 and 2022, and it's been apart on a shelf since.

StatusComplete, September 2026. Robot built 2021 to 2022, software rebuilt from scratch from August 2026
Joints12 servos, three per leg, 1.96 N.m each
Mass3.1 kg
BrainRaspberry Pi, PWM at 50 Hz, three IMUs on the trunk

Sheet 02 of 03/The machine

What the robot is

Only four of the twelve servos sit in the body. The rest are in the hip modules and drive the knees through a pushrod, so a servo's angle is never the same as the knee's angle. That layout got guessed wrong twice from photos and CAD before it was finally written down.

Sheet 03 of 03/Building it

Printing and assembling it

We printed the chassis and legs and wired the twelve servos into one driver board. We also built a handheld controller with two thumbsticks.

SolidWorks isometric view of the quadruped assembly with all four legs and twelve servos — *PL 02*The SolidWorks assembly. Four servos sit in the body and swing the hips, and the other eight sit in the hip modules and drive the thigh and the calf.

A bare rectangular robot chassis with four servos mounted and two steel rods running its length — *PL 03*The chassis before the legs go on. The four body servos and the two spine rods set every other dimension.

Close up of a 3D printed robot leg with a thin metal pushrod running from a servo to the lower leg — *PL 04*One leg. A ball jointed pushrod drives the knee, so the servo angle isn't the same as the joint angle.

A Raspberry Pi stacked with a blue servo driver board, jumper wires and a power lead attached — *PL 05*A Raspberry Pi on top of a PCA9685 driver board. It drives all twelve servos at 50 Hz, and that's the fastest the control can run.

An open handheld controller board with two joysticks, a microcontroller and four cylindrical batteries — *PL 06*The handheld controller, built on its own board with two thumbsticks, a microcontroller and four 18650 cells.

A white four-legged robot with its cover off lying on a floral rug beside a rectangular aluminium extrusion frame — *PL 10*Gray on the rug with its cover off, next to an aluminium extrusion frame, June 2022.

A white four-legged robot with its cover off standing on a floral rug inside an aluminium extrusion frame, thin lines running from the top rail to its body — *PL 11*Gray inside the frame, tied to the top rail with thin lines, June 2022. The cover is off and sits on the rug.