SO-101 parts list and cost

One follower arm or a leader + follower pair?

Buy one follower arm if you plan to drive it from code, for example a script or a coding agent that moves the joints. That's 6 servos, all the 1/345 gear version, one control board and one power supply.

Buy the pair if you want to collect training data with LeRobot. You move the leader arm by hand and the follower copies it. The repo says to buy the two-arm parts list for this setup. The pair needs 12 servos: 7 of the 1/345 gear (six for the follower, one for the leader), 2 of the 1/191 and 3 of the 1/147. The leader mixes gear ratios so it can hold up its own weight and still move easily by hand, per the LeRobot SO-101 docs. The Robot Studio also lists a bundle with all six leader servos on Alibaba.

Leader joint by joint, from the LeRobot docs: base / shoulder pan 1/191, shoulder lift 1/345, elbow flex 1/191, wrist flex 1/147, wrist roll 1/147, gripper 1/147.

7.4V or 12V servos?

The BOM uses the 7.4V STS3215, rated at 16.5 kg·cm stall torque at 6V and probably a little less on the 5V supply. The 12V version is rated at 30 kg·cm. If you pick 12V servos for the follower you also need a 12V 5A+ power supply instead of the 5V one. The leader arm always uses 7.4V servos. The Robot Studio found 7.4V was enough for its own use.

Print it yourself or buy a kit?

If you have a printer, the repo's tested settings are PLA+, a 0.4mm nozzle at 0.2mm layer height (or 0.6mm at 0.4mm) and 15% infill, on printers like the Prusa MINI+, Ender 3 or Bambu Lab A/P/X series. There are 14 distinct parts. Nine of them are shared by both arms, so set those to quantity 2 for a pair, and print only the mounting plate that matches your control board.

No printer? The repo's printing services page points to Craftcloud3d for the US and Europe and PCBWay for China. It also links Seeed Studio's printed frame, listed at $31.90.

A kit saves you the sourcing, and some save you the printing too. WowRobo, one of the vendors the repo lists, has three SO-101 packages: printed parts and 12 servos for $199, an unassembled leader + follower kit with a camera for $259, and an assembled pair with a camera for $299. The repo also lists Seeed Studio, PartaBot, ForgeMotion Labs, RobotEd, Robonine, Autodiscovery and others. Check what each kit leaves out, such as power supplies, clamps or the camera, before you compare it to the $229.88 BOM.

• Build the $100-class SO-101 open-source robot arm

Where people get stuck

Servo IDs. New STS3215 servos usually ship with ID 1, and every motor on the bus needs its own ID. LeRobot's setup command does this one motor at a time, starting with the gripper (ID 6). Only one motor can be plugged into the board at that step, with nothing daisy-chained to it. Reused motors from another robot almost always need this step too.

Power and cables. If setup throws an error, check the power supply, the USB cable and the 3-pin motor cable. The LeRobot docs warn that the power cable can slip out while you handle the board. On a Waveshare board, both jumpers have to be on the B channel (USB). On Linux you may need `sudo chmod 666 /dev/ttyACM0` to get access to the port.

Calibration. You put every joint in the middle of its range, press Enter, then move each joint through its full range. Do it for both arms, and take your time, because calibration is what lets a model trained on one SO-101 run on another.

Mixed-up leader servos. All three leader gear ratios are STS3215s at the same price, so label them when they arrive and check the joint list above before you install each one.

Next builds to read

Once the arm is calibrated, these are SO-101 builds with code you can run. If you're still picking an arm, see SO-101 vs SO-100 and the best robot arm under $200.

• Teach an SO-101 arm to pick and place with LeRobot
• Run SmolVLA on an SO-101 so it follows plain-English tasks
• Let a coding agent drive an SO-101 to paint or draw
• Put an SO-101 arm on wheels with LeKiwi
• Livestream and remote-control your SO-101 arm from a web app

Sources

Parts, quantities, US/EU/China/Japan prices, servo torque and print settings come from The Robot Studio's SO-ARM100 README (BOM totals re-checked Nov 3, 2026). Retail re-price of the same lines: Oct 30, 2026, on the seller pages linked in the answer note.

Common questions

What to build next

Builds that share a board, robot or agent with this one.

• Teach an SO-101 arm to pick and place with LeRobotAlso built on the SO-101 arm
• Build the $100-class SO-101 open-source robot armAlso built on the SO-101 arm
• Run SmolVLA on an SO-101 so it follows plain-English tasksAlso built on the SO-101 arm
• Use a folding phone as a controller for an SO-101 gripperAlso built on the SO-101 arm
• Livestream and remote-control your SO-101 arm from a web appAlso built on the SO-101 arm
• Put an SO-101 arm on wheels with LeKiwiAlso built on the SO-101 arm