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Attach the shoulder to the motor 1 horns Loading 3D view…
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Set the shoulder over motor 1 so its holes line up with the horn Horn. The metal disc that fits on the end of a motor; printed parts screw onto it. Each motor ships with two, one with gear teeth around its edge for the driven end and one plain disc for the other end.Source: waveshare.com · lerobot/docs/source/so101.mdx#joint-1 src Screw it to the horns with 4 M3x6 M3x6. A screw size. M3 means a 3 mm thread, 6 means 6 mm long. It has a machine thread and goes into the threaded holes of a horn; the same size holds each printed part to its horn.Source: mantech.co.za · lerobot/docs/source/so101.mdx#joint-1 src lerobot/docs/source/so101.mdx#joint-1 — "Attach the shoulder part. Tighten the shoulder part with 4 M3x6mm screws on top and 4 M3x6mm screws on the bottom" check — Shoulder holes line up with the horn holes on both ends; 4 M3x6 top, 4 M3x6 bottom. Done when 8 screws in, 4 on top and 4 underneath, holes lined up at both ends.
lerobot/docs/source/so101.mdx#joint-1 "Attach the shoulder part. Tighten the shoulder part with 4 M3x6mm screws on top and 4 M3x6mm screws on the bottom" waveshare.com Follower step 4: clamp F3 horizontally along the inner slide at both ends of servo 1 SO-ARM100/STEP/SO101/SO101 Assembly.step placement check (viewer/public/geometry/placements.json): Rotation_Pitch_SO101 spans servo 1 (49%) and the servo 2 pocket (42%): the shoulder on the motor-1 horns Check: Shoulder holes line up with the horn holes on both ends; 4 M3x6 top, 4 M3x6 bottom.
Motor slot: shoulder_pan · ID 1 · STS3215 1:345 ·
7.4V servo on a 5V supply; 12V servo on a 12V 5A+ supply (optional variant);
How we placed it: Part role confirmed by placement in the upstream assembly STEP: Rotation_Pitch_SO101 spans servo 1 (49%) and the servo 2 pocket (42%): the shoulder on the motor-1 horns.
You need Shoulder Rotation/pitch (shoulder) rotation-pitch-so101 details STS3215 motor, 1:345 gear, code C001 Feetech STS3215 servo, 7.4V, 1:345 gear (C001) servo-sts3215-c001-345 approximation3D stand-in Stand-in shape: the 3D geometry or placement is not measured from the real part.
Qty 7 is the two-arm build (6 follower + 1 leader). A 12V variant with 30 kg.cm stall exists for the follower only and needs a 12V 5A+ supply (README). Includes two horns and a 3-pin cable per the assembly texts; kit contents are not itemised upstream. Geometry: the upstream repo's own simplified body `STEP/SO100/STS3215_03a.step` (Apache-2.0, single solid drawn to the datasheet, D-007 for where they differ) with its fused horn plates cut off and the datasheet ø6 x 3.4 output boss added, posed on the embedded vendor model's transform; the vendor mesh is not redistributed.
details M3x6 screw M3x6 screw m3x6 ×8 details Phillips screwdriver #0 · PH0 tool details Phillips screwdriver #1 · PH1 tool details Sources (3) lerobot/docs/source/so101.mdx#joint-1 — "Attach the shoulder part. Tighten the shoulder part with 4 M3x6mm screws on top and 4 M3x6mm screws on the bottom" waveshare.com (retrieved 2026-09-07) — Follower step 4: clamp F3 horizontally along the inner slide at both ends of servo 1 SO-ARM100/STEP/SO101/SO101 Assembly.step — placement check (viewer/public/geometry/placements.json): Rotation_Pitch_SO101 spans servo 1 (49%) and the servo 2 pocket (42%): the shoulder on the motor-1 horns How we placed it Part role confirmed by placement in the upstream assembly STEP: Rotation_Pitch_SO101 spans servo 1 (49%) and the servo 2 pocket (42%): the shoulder on the motor-1 horns.