SO-101 Safety

Safety Guidelines

Read these guidelines before powering on your SO-101 for the first time. The arm is lightweight but servos can apply enough force to cause injury or damage if operated incorrectly.

Servo Protection

The Feetech STS3215 servos are the most sensitive components in the SO-101. Incorrect handling can strip gears or burn out windings.

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Do not backdrive while powered Manually forcing a joint to move while power is applied can strip the servo gearbox. Always power down before repositioning the arm by hand.
  • Never manually override a joint while the arm is powered — always send a software stop command first
  • Avoid hitting joint travel limits repeatedly; configure software limits to stop before physical limits
  • If a servo emits a clicking or grinding sound, stop operation immediately and inspect for gear damage
  • Allow servos to cool between long recording sessions — sustained high-load positions generate heat
  • Do not exceed the rated payload (~500 g) at full arm extension

Power Safety

The SO-101 runs on 12V DC. Incorrect voltage or reversed polarity can permanently damage servos.

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Check polarity before connecting Verify the power connector polarity matches the servo bus polarity before first use. Reversed polarity can destroy all servos simultaneously with no visible warning.
  • Use a regulated 12V DC supply rated at 3A or higher
  • Never use a laptop charger or unregulated supply as a substitute
  • Inspect all servo cable connections before applying power after any reassembly
  • Keep the work area dry — never operate near liquids
  • Use a power strip with an accessible switch as a manual cut-off for the 12V supply

Build Quality & Maintenance

The SO-101 uses 3D-printed structural parts. Print quality and assembly tightness directly affect safe operation.

  • Re-check all screws after initial assembly — vibration can loosen hardware during first operation
  • Inspect all servo mounting screws monthly, or after any collision
  • Check for layer delamination or cracking in printed parts, especially at joint interfaces
  • Replace any printed part showing visible stress fractures before continuing operation
  • Use a minimum 20% infill density for structural parts; 40%+ recommended for servo mounts

Workspace Setup

The SO-101 is a lightweight arm, but an unsecured base can tip or slide during fast motions, creating a hazard.

  • Bolt or clamp the base securely to a sturdy table before first power-on
  • Keep hands and objects out of the arm's reach envelope during powered operation
  • Define a clear workspace area around the arm — avoid clutter that the arm could strike
  • For classroom or lab use, always have a second person present or visible during initial testing
  • Route USB and power cables away from joint travel paths to prevent snagging

Calibration Requirements

Calibration sets the servo zero positions. Operating without calibration or with stale calibration data can cause the arm to move unexpectedly.

Always re-calibrate after reassembly. If you disassemble any joint, re-run calibrate.py --robot.type=so101 before operating the arm. Calibration data stored from a previous configuration will produce incorrect joint zeros.
  • Run calibration on first power-on after assembly
  • Re-calibrate after any joint disassembly, servo replacement, or collision
  • Verify all joints reach their calibration positions without obstruction before recording

Emergency Procedures

The SO-101 has no hardware e-stop. Use the software and hardware methods below.

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Emergency stop Disconnect the USB cable to immediately cut communication to the arm. The arm will hold its current position until power is also removed. Disconnect the 12V supply to fully de-energize.
  • Software stop: Press Ctrl+C in the terminal running lerobot scripts — the arm will disable servo torque and go limp
  • Hardware stop: Unplug the USB cable — the arm holds position but stops receiving commands
  • Full de-energize: Unplug the 12V power supply — all servos disengage; support the arm before doing this to prevent it from falling under gravity
  • Keep the workspace clear so you can reach the USB cable or power switch quickly

Back to Setup

Follow the setup guide for the full assembly and software walkthrough.

Setup Guide Community & FAQ SO-101 Hub