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Robotics Studio

Dumbo, a hybrid octopus robot that walks on four legs and rolls on four retractable casters.

MECE 4611, ColumbiaFall 2026 · in progressPreliminary CAD

The course builds a walking robot from a fixed kit: eight Hiwonder LX-16A servos, a Raspberry Pi, and a 12 V pack limited to 30 W. I'm building Dumbo, which I worked through mass, joint torque, gait stability, power, and run time at the concept stage before moving it into CAD.

Dumbo in CAD

Preliminary CAD · Fusion 360

An internal endoskeleton carries the electronics and the shell is only a skin. The four caster arms ride on slides so they can lift clear of the ground and let Dumbo walk as a plain quadruped on carpet. Front and rear casters on each side share one mount at the side midpoint, and a minimum-distance check across twelve gait phases confirms the legs clear the casters everywhere.

Dumbo next to a soda can for scaleDumbo with a transparent shell, showing the endoskeleton, hip pods and electronics insideDumbo endoskeleton with the shell removed: deck plate, battery, Raspberry Pi, servo controller and eight servosExploded view of Dumbo: shell, electronics stack, deck, legs and caster armsClose-up of a hip pod with its two LX-16A servos and the four-bar knee pushrodClose-up of the caster slides that raise the caster arms for quadruped walking

The fork thigh for the LX-16A servo is published on GrabCAD.

Design Basis

  • Servo: 52 g, 1.67 N·m stall at 7.4 V, about 1.35 N·m on the 6 V bus
  • Assumed continuous torque: 0.55–0.85 N·m
  • Course limit of 1 A per motor, so 6 W each
  • 12 V, 3000 mAh battery: about 29 Wh usable, 30 W output limit
  • Estimated 16–17 W average, about 29 W peak, roughly 1.75 h ideal run time
  • Every figure is a design assumption to be replaced by measurement once hardware exists

The Concept

Hybrid octopus robot · concept sketches

Four driven legs move the body while four folding, height-adjustable caster legs carry about 30% of the weight during a hybrid trot. Two servos sit at each hip; a four-bar drives the knee through a slender pushrod.

  • 1.27 kg mass budget
  • 0.61 N·m governing hip load (0.88 without casters)
  • 2.7× stall margin in hybrid mode
Dumbo concept sketch with key dimensionsDumbo with the shell removed, showing hip pods, battery, Raspberry Pi and servo controllerDumbo driven leg: hip servos, four-bar knee linkageDumbo hip torque and operating modes calculation

Working With

Hiwonder LX-16A servosRaspberry Pi 4Four-bar linkagesFree-body analysisGait and stability analysisFusion 360