Jiahe Tang

Overview

The SO-101 is the open-source successor to the SO-100 — a low-cost 6-DOF manipulator built from 3D-printed parts and serial bus servos, designed by TheRobotStudio and used worldwide as a base platform for imitation-learning research. I run two of them as a leader/follower pair: one arm is moved by hand, the joint states stream over serial, and the follower replays them — that's the data-collection rig. Recorded demonstrations then train a policy that drives the arm on its own.

Build process

• Printed and assembled both arms; calibrated joint offsets and IDs
• Brought up the Jetson companion computer (flashing, env, serial I/O)
• Built a bench rig with a battery power rail and audible start/end cues for clean episode recording
• Teleoperated the leader to record demonstration episodes
• Trained policies on the recorded dataset; evaluated rollout success on the bench

Technical details

• 6 DOF per arm + gripper; Feetech STS/STS-style serial bus servos
• Leader/follower teleoperation over USB serial (pyserial-level control)
• Jetson Orin Nano companion computer for logging and training
• Python data pipeline: episode logging, dataset structuring, policy training
• Battery-powered rig (8.3 V rail) for repeatable bench recording

Key learnings

• Bus-servo ecosystems lie: reported IDs and positions can be stale or phantom — going to raw serial reads is the only ground truth
• Clean data beats clever training: disciplined episode start/end markers improved dataset quality more than any training tweak
• Hardware quirks (a "scrambled" arm) usually mean the wrong board or an ID artifact, not broken servos

Overview

Jansen's linkage turns one rotating crank into a foot path that is nearly flat and long on the ground, and lifts cleanly over the top — a walking gait from a single motor, no control software required. I built the full leg geometry in CAD from the canonical "holy numbers", then cut and assembled an eight-legged machine around a central crankshaft.

Build process

• Reconstructed the leg in CAD from Jansen's published link lengths; sketched every bar and pin joint
• Simulated the foot path to verify the flat stance before cutting (the hero animation is this validation, live)
• Laser-cut bars and plates from plywood on the school's 30 W cutter; printed gears for the crank drive
• Assembled v1: legs cycled and the machine walked — but the frame flexed and folded under its own weight
• V2: redesigned side plates and bracing; finalized a clean set of nine DXF cut files

Technical details

• Planar 11-bar linkage per leg (Jansen's "holy numbers", mm)
• Crank radius 15 mm; fixed pivots on a 38 × 7.8 mm ground link
• Simulated foot path: ≈83 mm stride, ~82% of it near-flat stance
• Legs paired in phase opposition on a shared crankshaft
• Gear-driven crank; structure in laser-cut plywood + printed connectors

Key learnings

• Geometry is free; structure is not — the linkage was right, the frame was the failure
• Sketch-grade CAD ≠ cut-ready CAD: joints tangent to bar edges sever parts on the cutter
• Duplicate stacked lines in DXFs burn edges — a clean-up pass is part of design, not an afterthought

Overview

Quasi-direct drive means the motor spins fast with low gearing (typically 6–10:1), so the rotor's own inertia can back-drive the gearbox. That makes the joint compliant and force-controllable — you can push a QDD joint and it gives, which is why research humanoids use them. Instead of buying one, I built one: BLDC + VESC + encoders + a 3D-printed planetary gearbox of my own design.

Build process

• Sized the motor and gear ratio against a robot-knee torque budget
• Generated parametric gearbox plates and gear DXFs/STLs, then printed and iterated fit
• Wired the VESC open-source controller; configured FOC over USB
• Added magnetic encoder sensing on the output shaft for true position feedback
• Bench testing: step responses, torque limits, thermal behavior

Technical details

• Outrunner BLDC motor, hobby-class [VERIFY]
• VESC open-source ESC running FOC current control
• Magnetic encoders: motor-side + output-shaft angle
• Single-stage planetary reduction, 3D-printed gears
• Closed-loop position control on the output shaft

Key learnings

• Back-drivability is a design choice, not a spec-sheet number — ratio selection is the whole game
• Printed gears mesh fine at these torques if you print them big enough and compensate hole tolerance
• Open-source motor control (VESC) collapses the electronics barrier: the hard part is mechanical

Overview

The Colibri is a classic 1.5 m RES-style thermal glider. I built it from the published vector plan set — cutting parts, assembling the fuselage and tail, and finishing the wing with its carbon spar. Where my first foam plane was a repair job that taught me why things break, the Colibri was a clean-sheet build that taught me why things fly: trimming, center-of-gravity, and how spar stiffness buys launch survival.

Build process

• Sourced the Colibri 1500 plan set (vector CAD + PDF build guide)
• Cut and assembled structure; mounted radio gear and control linkages
• Used the glider as the experimental platform for my Extended Essay: spar-material stiffness testing
• 3D-printed a display model of the airframe from the same geometry

Technical details

• 1500 mm wingspan RES-style thermal glider
• Carbon-spar wing; balsa/foam structure per plan set
• Standard RC gear: receiver, two servos on the tail, launch by hand/bungee
• Extended Essay: three-point bending tests of spar materials

Key learnings

• Repair is the best teacher — every failure isolates one design decision
• Materials testing on paper ≠ in the air: measured stiffness only matters through the loads it actually sees
• Building from someone else's plans, then deviating where you understand why — that's the growth path