Leader arm · Step 26 of 26 · L-071

Daisy-chain the motor cables and connect motor 1 to the board

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Do this

Leader motors are always 7.4V: use the 5V supply, never 12V (README, Seeed).

Run a cable from each motor to the next one down: 6 to 5, 5 to 4, 4 to 3, 3 to 2, 2 to 1.
src
- check — Chain runs 6→5→4→3→2→1; motor 1 (shoulder pan, ID 1) to the controller board; power and USB connected.
- lerobot/docs/source/so101.mdx#2-set-the-motors-ids-and-baudrates — "plug the 3-pin cable from each motor to the next one, and the cable from the first motor (the 'shoulder pan' with id=1) to the controller board"
Plug the cable from motor 1 (the
shoulder pan
Shoulder pan. Motor 1's joint, in the base. "Pan" means turning sideways, the way a camera pans; it swings the whole arm left and right.Source: lerobot/docs/source/so101.mdx#2-set-the-motors-ids-and-baudrates
motor,
ID
Motor ID. The number 1 to 6 written into each motor before building, so the control board can tell the motors apart on one cable chain. 1 is the motor in the base, 6 is the gripper.Source: lerobot/docs/source/so101.mdx#2-set-the-motors-ids-and-baudrates
1) into the
control board.
Control board. The small circuit board (a Waveshare bus servo adapter) that connects to your computer by USB and to motor 1 by a 3-pin cable. It powers and talks to all six motors through the chain and sits on a printed plate on the base.Source: lerobot/docs/source/so101.mdx#2-set-the-motors-ids-and-baudrates · waveshare.com
src
- check — Chain runs 6→5→4→3→2→1; motor 1 (shoulder pan, ID 1) to the controller board; power and USB connected.
- lerobot/docs/source/so101.mdx#2-set-the-motors-ids-and-baudrates — "plug the 3-pin cable from each motor to the next one, and the cable from the first motor (the 'shoulder pan' with id=1) to the controller board"
Connect the power supply and the USB cable to the board. Use the supply that matches your motors: 5V for the standard 7.4V motors.
src
- check — Chain runs 6→5→4→3→2→1; motor 1 (shoulder pan, ID 1) to the controller board; power and USB connected.
- warnings — Leader motors are always 7.4V: use the 5V supply, never 12V (README, Seeed).

Done when The chain runs 6, 5, 4, 3, 2, 1; motor 1 plugs into the board; power and USB are connected.

Upstream numbers the follower's steps; this leader step is the same build step (extends F-071).

lerobot/docs/source/so101.mdx#2-set-the-motors-ids-and-baudrates"plug the 3-pin cable from each motor to the next one, and the cable from the first motor (the 'shoulder pan' with id=1) to the controller board"

waveshare.comFollower step 19

Check: Chain runs 6→5→4→3→2→1; motor 1 (shoulder pan, ID 1) to the controller board; power and USB connected.

Motor slot: shoulder_pan · ID 1 · STS3215 1:191 · 7.4V servo on a 5V supply;

Motor 1 · shoulder pan

The motor you labelled 1: STS3215 motor,

1:191

Gear ratio. The number on the motor's label, such as 1:345. The motor inside turns 345 times for one turn of the output. The follower arm uses 1:345 at all six joints. The leader arm mixes 1:191, 1:345 and 1:147, so check the label before fitting a motor.Source: lerobot/docs/source/so101.mdx#step-by-step-assembly-instructions · SO-ARM100/README.md#sourcing-parts

gear, code C044. details

You need

3-pin motor cable3-pin servo bus cable servo-cable-3pin
unverifiedno source yet
Not checked yet: no public source confirms this. Treat it as a best guess and report what you find.
Used to daisy-chain motors and reach the controller board. Not itemised in the README BOM; the assembly texts assume they come with the servos. Qty 6 per arm = the six cable bodies (Component1–4, 6, 7) plus two 050375033 connector housings modelled in SO101 Assembly.step; kit-shipped count still unsourced.
details
Control boardMotor control board (Waveshare bus servo adapter) motor-control-board
approximation3D stand-in
Stand-in shape: the 3D geometry or placement is not measured from the real part.
One per arm. Set both jumpers to the B (USB) channel before configuring motors (LeRobot troubleshooting). Geometry: the assembly STEP embeds a vendor PCB model of unknown provenance; the pipeline exports a bounding-box primitive instead (approximation).
details

Cables in the 3D view

the board → motor 1board → shoulder pan cable-board-to-shoulder-pan
approximation3D stand-in
Stand-in shape: the 3D geometry or placement is not measured from the real part.
motor 1 → motor 2shoulder pan → shoulder lift cable-shoulder-pan-to-shoulder-lift
approximation3D stand-in
Stand-in shape: the 3D geometry or placement is not measured from the real part.
motor 2 → motor 3shoulder lift → elbow flex cable-shoulder-lift-to-elbow-flex
approximation3D stand-in
Stand-in shape: the 3D geometry or placement is not measured from the real part.
motor 3 → motor 4elbow flex → wrist flex cable-elbow-flex-to-wrist-flex
approximation3D stand-in
Stand-in shape: the 3D geometry or placement is not measured from the real part.
motor 4 → motor 5wrist flex → wrist roll cable-wrist-flex-to-wrist-roll
approximation3D stand-in
Stand-in shape: the 3D geometry or placement is not measured from the real part.
motor 5 → motor 6wrist roll → gripper cable-wrist-roll-to-gripper
approximation3D stand-in
Stand-in shape: the 3D geometry or placement is not measured from the real part.

Sources (2)

Upstream numbers the follower's steps; this leader step is the same build step (extends F-071).

lerobot/docs/source/so101.mdx#2-set-the-motors-ids-and-baudrates — "plug the 3-pin cable from each motor to the next one, and the cable from the first motor (the 'shoulder pan' with id=1) to the controller board"
waveshare.com (retrieved 2026-09-07) — Follower step 19

Leader arm built.

That was the last of the 26 steps. Calibration and the LeRobot software setup are outside this guide; the upstream page carries on from here.

Continue on the LeRobot SO-101 page → Build the follower arm Something's wrong