Motors · Follower 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 C001.
1:345
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.
- Only if you bought the optional 12V motors (STS3215 motor, 12V, 1:345 gear (optional follower variant)): use a 12V 5A+ supply instead.
- Joint: elbow_flex · bus ID 3 · STS3215 1:345
- Default part: Feetech STS3215 servo, 7.4V, 1:345 gear (C001)
servo-sts3215-c001-345 - Standard: Feetech STS3215 servo, 7.4V, 1:345 gear (C001)
servo-sts3215-c001-345, 7.4V servo, 5V supply. - Optional: Feetech STS3215 servo, 12V, 1:345 gear (optional follower variant)
servo-sts3215-12v-345, 12V servo, 12V 5A+ supply. Optional follower-only variant. SVRC's "12V power supply" applies to this variant only (D-002).
Steps for this motor
- F-030 Fit both horns on motor 3 (elbow flex)
- F-031 Insert motor 3 into the upper arm
- F-032 Connect the forearm to the motor 3 horns
Sources (6)
- lerobot/docs/source/so101.mdx#step-by-step-assembly-instructions — "The follower arm uses 6x STS3215 motors with 1/345 gearing"
- lerobot/docs/source/so101.mdx#2-set-the-motors-ids-and-baudrates — setup script names the joint and assigns id 3 bottom-up
- wiki.seeedstudio.com (retrieved 2026-09-07) — servo table: F1–F6 = ST-3215-C001 1:345
- SO-ARM100/README.md#sourcing-parts — 7.4V servos; 5V power supply
- SO-ARM100/README.md#sourcing-parts — IMPORTANT note: 12V version needs a 12V 5A+ power supply
- roboticscenter.ai (retrieved 2026-09-07) — "12V power supply (3A minimum)"