Leader arm · Step 24 of 26 · L-063

Attach the trigger approximation3D stand-in

Loading 3D view…

Do this

Set the trigger onto the geared
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
and screw it on 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#gripper--handle — Leader: "Attach the follower trigger with 4 M3x6mm screws."
- waveshare.com — Leader step 18: onto the gear-equipped steering wheel
- check — Trigger on the geared horn with 4 M3x6; the finger loop hangs ahead of the grip.
Turn it so the finger loop hangs down and ahead of the grip. The holes let it sit in four positions; only the upstream photo fixes which one.
src
- check — Trigger on the geared horn with 4 M3x6; the finger loop hangs ahead of the grip.
- instructions — The trigger's four M3 holes sit on the same 7 mm radius as the horn's, so it fits in four positions 90 degrees apart; the upstream leader photo shows the loop pointing down and toward the gripper tip, and the 3D view uses that one (approximation: the loop's rest angle is not fixed by any part).
- huggingface.co — finished leader: trigger loop below and ahead of the gripper servo, in front of the grip

Done when The trigger is on the geared horn with 4 screws and the loop hangs ahead of the grip.

lerobot/docs/source/so101.mdx#gripper--handleLeader: "Attach the follower trigger with 4 M3x6mm screws."

waveshare.comLeader step 18: onto the gear-equipped steering wheel

SO-ARM100/STEP/SO101/Leader_Specific/Trigger_SO101.stepfour r=1.6 holes at radius 7.0 mm about the horn face (z=0), plate 3.5 mm

huggingface.cofinished leader: trigger loop below and ahead of the gripper servo, in front of the grip

Notes: The trigger's four M3 holes sit on the same 7 mm radius as the horn's, so it fits in four positions 90 degrees apart; the upstream leader photo shows the loop pointing down and toward the gripper tip, and the 3D view uses that one (approximation: the loop's rest angle is not fixed by any part).

Check: Trigger on the geared horn with 4 M3x6; the finger loop hangs ahead of the grip.

Motor slot: gripper · ID 6 · STS3215 1:147 · 7.4V servo on a 5V supply;

Motor 6 · gripper

The motor you labelled 6: 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

Leader triggerLeader trigger trigger-so101 details
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
M3x6 screwM3x6 screw m3x6 ×4 details
Phillips screwdriver #0 · PH0 tool details
Phillips screwdriver #1 · PH1 tool details

Sources (4)

lerobot/docs/source/so101.mdx#gripper--handle — Leader: "Attach the follower trigger with 4 M3x6mm screws."
waveshare.com (retrieved 2026-09-07) — Leader step 18: onto the gear-equipped steering wheel
SO-ARM100/STEP/SO101/Leader_Specific/Trigger_SO101.step — four r=1.6 holes at radius 7.0 mm about the horn face (z=0), plate 3.5 mm
huggingface.co (retrieved 2026-09-07) — finished leader: trigger loop below and ahead of the gripper servo, in front of the grip