Leader arm · Step 18 of 26 · L-050

Insert motor 5 into the wrist holder

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Do this

Route the cables before inserting motor 5: "otherwise it is easy to tear the wire" (Waveshare).

Take the motor you labelled 5.
src
- servos.yaml · leader/wrist_roll — ID 5 · STS3215 1:147 · Feetech STS3215 servo, 7.4V, 1:147 gear (C046)
- F-002 · check — Each motor answers on its own ID 1–6, bottom joint = 1, gripper = 6; leader and follower motors are labelled and kept apart.
Before the motor goes in, feed both cables through the wrist holder. The wire tears easily if you do this afterwards.
src
- warnings — Route the cables before inserting motor 5: "otherwise it is easy to tear the wire" (Waveshare).
- check — Motor 5 held by 2 motor-tab screws at the front; both cables routed through the holder before the motor went in.
- waveshare.com — Follower step 14: wire first, then insert the servo gear side first, gear facing up
Slide motor 5 in gear end first, with the gear facing up.
src
- orientation note — Gear side goes in first, gear facing up (Waveshare).
- waveshare.com — Follower step 14: wire first, then insert the servo gear side first, gear facing up
- servos.yaml · leader/wrist_roll — ID 5 · STS3215 1:147 · Feetech STS3215 servo, 7.4V, 1:147 gear (C046)
Fix it with 2 small
self-tapping screws
Self-tapping screw. A screw that cuts its own thread into the plastic as you drive it. These are the smallest screws in the kit and hold each motor in its printed bracket. No public source confirms the exact size yet (D-001).Source: lerobot/docs/source/so101.mdx#joint-1 · waveshare.com
at the front.
src
- lerobot/docs/source/so101.mdx#joint-5 — "Insert motor 5 into the wrist holder and secure it with 2 M2x6mm front screws."
- check — Motor 5 held by 2 motor-tab screws at the front; both cables routed through the holder before the motor went in.

Done when 2 screws in at the front, and both cables went through the holder before the motor did.

Upstream numbers the follower's steps; this leader step is the same build step (extends F-050).

lerobot/docs/source/so101.mdx#joint-5"Insert motor 5 into the wrist holder and secure it with 2 M2x6mm front screws."

waveshare.comFollower step 14: wire first, then insert the servo gear side first, gear facing up

SO-ARM100/STEP/SO101/SO101 Assembly.stepplacement check (viewer/public/geometry/placements.json): Wrist_Roll_Pitch (SO100-named solid) encloses 97% of servo 5: the wrist holder

Orientation: Gear side goes in first, gear facing up (Waveshare).

Check: Motor 5 held by 2 motor-tab screws at the front; both cables routed through the holder before the motor went in.

Motor slot: wrist_roll · ID 5 · STS3215 1:147 · 7.4V servo on a 5V supply;

How we placed it: Part role confirmed by placement in the upstream assembly STEP: Wrist_Roll_Pitch (SO100-named solid) encloses 97% of servo 5: the wrist holder.

Motor 5 · wrist roll

The motor you labelled 5: STS3215 motor,

1:147

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 C046. details

You need

STS3215 motor, 1:147 gear, code C046Feetech STS3215 servo, 7.4V, 1:147 gear (C046) servo-sts3215-c046-147
approximation3D stand-in
Stand-in shape: the 3D geometry or placement is not measured from the real part.
Geometry: the upstream repo's own simplified body STEP/SO100/STS3215_03a.step (Apache-2.0, D-007) with its fused horn plates cut off and the datasheet ø6 x 3.4 boss added, posed on the embedded vendor model's transform; the vendor mesh is not redistributed.
details
Wrist holderWrist roll/pitch (wrist holder) wrist-roll-pitch-so101 details
Small self-tapping screw (motor screw)Motor-tab screw, M2-class self-tapping motor-tab-screw
unverifiedno source yet
Not checked yet: no public source confirms this. Treat it as a best guess and report what you find.
Sources disagree and no kit has been measured (D-001, open). Upstream default = the assembly STEP, which models 24 positions per arm: 22 x "Type I Cross Recessed Fillister Head Tapping Screw ANSI B18.6.4 1-42 x 0.1875 Type AB" (≈ ø1.9 x 4.8 mm) and, for the two screws that enter motor 1 from above, 2 x "0-48 x 0.1875" (≈ ø1.5 x 4.8 mm). Vendor/doc variants: LeRobot "M2x6mm screws (smallest screws)"; Waveshare "pointed screws". The Feetech datasheet gives no tab screw and ships "No Accessories". Qty = count used across the LeRobot steps (24 + 21 positions); a kit inventory settles the spec and count. Seating per screw is read from the STEP by the pipeline (shank through a hole of which printed part) and drives what the 3D view shows at each step.
×2 details
Phillips screwdriver #0 · PH0 tool details
Phillips screwdriver #1 · PH1 tool details

Cables in the 3D view

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.

Sources (3)

Upstream numbers the follower's steps; this leader step is the same build step (extends F-050).

lerobot/docs/source/so101.mdx#joint-5 — "Insert motor 5 into the wrist holder and secure it with 2 M2x6mm front screws."
waveshare.com (retrieved 2026-09-07) — Follower step 14: wire first, then insert the servo gear side first, gear facing up
SO-ARM100/STEP/SO101/SO101 Assembly.step — placement check (viewer/public/geometry/placements.json): Wrist_Roll_Pitch (SO100-named solid) encloses 97% of servo 5: the wrist holder

How we placed it

Part role confirmed by placement in the upstream assembly STEP: Wrist_Roll_Pitch (SO100-named solid) encloses 97% of servo 5: the wrist holder.