Cheapest robot arm to build
The SO-101 is the cheapest capable arm to build: a leader and follower pair costs about $230 to $330 in parts, and a follower alone is roughly half that, using Feetech STS3215 servos and 3D printed links. If you want a stepper-driven six axis arm instead, Thor is the cheapest open design at about $300 to $450 in parts, but it takes far more assembly.
What matters
- Total parts cost including power supplies and controller boards, not just motors.
- Whether you need a 3D printer (all of these do, or you pay for printed parts).
- Software you get for free: LeRobot for SO-101, G-code and a GUI for Thor and Moveo.
- Build time and skill: servo arms take an afternoon; stepper arms take days of wiring and tuning.
- Payload and precision you actually need; cheap servo arms lift a few hundred grams.
Our picks
| Pick | Why | Where to buy |
|---|---|---|
| SO-101 (SO-ARM101) Cheapest arm that does real imitation learning | About $230 for a leader and follower pair from the official BOM, with LeRobot handling calibration, recording and training. Twelve STS3215 servos at about $20 each are most of the cost. | Seeed Studio: $240.00 (unverified) servo kit for both arms, no printed parts Seeed Studio: $277.99 servo kit for both arms, no printed parts Seeed Studio: $20.00 single servo |
| Thor Cheapest six axis stepper arm | Fully printed with seven NEMA 17 steppers; the project puts parts near 350 EUR. No kit exists, so you source every part from the BOM. | StepperOnline: $26.91 (unverified) single; geared motor, Thor needs 3 |
| BCN3D Moveo Classroom-style printed arm on Arduino and RAMPS | Five axes plus a servo gripper on an Arduino Mega with RAMPS, about $500 to $800 in parts today. Well known, but there is no official wiring diagram. | Arduino: EUR 52.80 single; incl. VAT |
| Koch v1.1 Low-cost arm with DYNAMIXEL servos | The first LeRobot reference arm, about $480 to $560 for a pair; costs more than SO-101 but uses ROBOTIS servos. | RoboSavvy: GBP 27.20 single XL330-M288-T servo |
FAQ
Can I build just one SO-101 arm?
Yes. The follower alone costs about half the pair. You need the leader only for teleoperation; without it you control the arm from code or another input.
Do I need a 3D printer?
For all four, yes, or you buy printed parts. Seeed sells SO-101 printed parts for about $30.
Why not a $50 hobby servo arm kit?
Cheap PWM servo kits have no position feedback, so they cannot record demonstrations or close the loop. The STS3215 reports its position, which LeRobot relies on.
Why is the BOM total lower than retail kits?
BOM totals often assume Alibaba or AliExpress prices and leave out shipping. Expect US retail to land near the top of each range.
Sources: github.com · huggingface.co · thor.angel-lm.com · github.com · github.com · huggingface.co · www.seeedstudio.com · www.seeedstudio.com