Motors · Leader arm
Motor 3 · elbow flex
Elbow flex. Motor 3's joint, between the upper arm and the forearm. "Flex" means bending.Source: lerobot/docs/source/so101.mdx#2-set-the-motors-ids-and-baudrates · lerobot/docs/source/so101.mdx#joint-3
elbow flex
Elbow flex. Motor 3's joint, between the upper arm and the forearm. "Flex" means bending.Source: lerobot/docs/source/so101.mdx#2-set-the-motors-ids-and-baudrates · lerobot/docs/source/so101.mdx#joint-3Which motor goes here
- Use the motor you labelled 3. It must be a STS3215 motor, gear, code C044.
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 - Power it from a 5V supply; that is the supply for the standard 7.4V motor.
- Joint: elbow_flex · bus ID 3 · STS3215 1:191
- Default part: Feetech STS3215 servo, 7.4V, 1:191 gear (C044)
servo-sts3215-c044-191 - Standard: Feetech STS3215 servo, 7.4V, 1:191 gear (C044)
servo-sts3215-c044-191, 7.4V servo, 5V supply. Leader arm is always 7.4V on the 5V supply; no 12V variant exists for it (README).
Steps for this motor
- L-030 Fit both horns on motor 3 (elbow flex)
- L-031 Insert motor 3 into the upper arm
- L-032 Connect the forearm to the motor 3 horns
Sources (4)
- lerobot/docs/source/so101.mdx#step-by-step-assembly-instructions — leader table row "Elbow Flex": motor 3, 1 / 191
- wiki.seeedstudio.com (retrieved 2026-09-07) — servo table: L3 = 1:191
- SO-ARM100/README.md#sourcing-parts — leader bundle footnote
- SO-ARM100/README.md#sourcing-parts — 7.4V servos; 5V power supply