Leader arm servo with the wrong gear ratio at a joint
Also reported as: leader arm too stiff · leader arm collapses
Symptoms
- Leader joint is hard to move by hand or does not hold its own weight
Cause
The SO-101 leader uses three ratios (1:191 at joints 1 and 3, 1:345 at joint 2, 1:147 at joints 4–6); a 1:345 follower servo or a swapped leader servo was fitted at the wrong joint.
Fix
Compare each leader servo's product code (C044 = 1:191, C001 = 1:345, C046 = 1:147) against the joint table before assembly; swap the servo, then re-run motor setup.
Related steps
- L-002 Set motor IDs 1–6 and baud rate before assembly
- L-011 Seat motor 1 in the base
- L-021 Slide motor 2 in from the top and fasten
- L-031 Insert motor 3 into the upper arm
- L-042 Slide in motor 4 and fasten
- L-050 Insert motor 5 into the wrist holder
- L-062 Insert the gripper motor and fit its horn
Related parts
- Feetech STS3215 servo, 7.4V, 1:191 gear (C044)
- Feetech STS3215 servo, 7.4V, 1:345 gear (C001)
- Feetech STS3215 servo, 7.4V, 1:147 gear (C046)
Sources (3)
- lerobot/docs/source/so101.mdx#step-by-step-assembly-instructions — leader gear-ratio table and rationale
- wiki.seeedstudio.com (retrieved 2026-09-07) — "make sure that the servo joint IDs and gear ratios strictly correspond to those of the SO-ARM101"
- SO-ARM100/README.md#sourcing-parts — product codes