feat(calibration): add automatic calibration for SO101 leadera and follower w/ Feetech STS servos

[IsaacSinn]

Type / Scope

• Type: Feature
• Scope: calibration, motors/feetech

Summary / Motivation

Adds a fully automated calibration CLI (lerobot-auto-calibrate-feetech) for SO-101 follower arms with Feetech STS3215 servos. The script drives each joint to its mechanical limits at low torque to measure the full range of motion no manual movement required.

Manual calibration requires the user to physically move each joint through its full range while following prompts. This is error-prone (inconsistent ranges, missed limits) and tedious, especially when calibrating multiple arms. Auto-calibration produces consistent, repeatable results with a single command.

Related issues

• Related: N/A — new feature contribution from Maker-Mods

What changed

• src/lerobot/motors/feetech/auto_calibration.py (new): FeetechCalibrationMixin with stall detection, mechanical range measurement, and WritePosEx utilities
• src/lerobot/motors/feetech/calibration_defaults.py (new): shared constants and default calibration parameters
• src/lerobot/motors/feetech/feetech.py: added FeetechCalibrationMixin to FeetechMotorsBus class inheritance
• src/lerobot/scripts/lerobot_auto_calibrate_feetech.py (new): CLI entry point with 5-stage calibration workflow (init → unfold → calibrate joints 2–6 → calibrate joint 1 → persist)
• pyproject.toml: added lerobot-auto-calibrate-feetech console script entry point
• docs/source/so101.mdx: added Auto Calibrate documentation section with usage and arguments table
• No breaking changes. Existing calibration workflows are unaffected.

How was this tested (or how to run locally)

• Tested on a physical SO-101 follower arm (macOS, ubuntu 22 24, Python 3.12)

• Calibration output saved to ~/.cache/huggingface/lerobot/calibration/robots/so_follower/default.json — same format as lerobot-calibrate

• Reproduce with:

  lerobot-auto-calibrate-feetech --port /dev/ttyUSB0 --save --robot-id my_follower
  

Checklist (required before merge)

• Linting/formatting run (ruff check and ruff format pass)
• Documentation updated (docs/source/so101.mdx)
• CI is green!

Reviewer notes

• This adds a mixin (FeetechCalibrationMixin) to FeetechMotorsBus — reviewers should verify the mixin methods don't conflict with existing SerialMotorsBus methods
• The script uses low torque and stall detection for safety, but reviewers with hardware should test on their own arms
• Anyone in the community is free to review the PR