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The SO-101 is an affordable 6-DOF robotic arm that uses Feetech STS3215 servo motors. It’s part of the SO follower series and is well-suited for teleoperation and imitation learning tasks.

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Overview

The SO-101 features:
  • 6 degrees of freedom (5 arm joints + gripper)
  • Feetech STS3215 servo motors
  • USB serial communication
  • Position control mode
  • Optional camera integration
  • Affordable hardware components

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Hardware Specifications

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Motors

The SO-101 uses the following motor configuration:
Motor NameIDModelNormalization Mode
shoulder_pan1STS3215Degrees or Range[-100,100]
shoulder_lift2STS3215Degrees or Range[-100,100]
elbow_flex3STS3215Degrees or Range[-100,100]
wrist_flex4STS3215Degrees or Range[-100,100]
wrist_roll5STS3215Degrees or Range[-100,100]
gripper6STS3215Range[0,100]
By default, SO-101 uses degree normalization (use_degrees=True) for backward compatibility with existing datasets and policies.

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Installation

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Hardware Setup

  1. Connect the SO-101 arm to your computer via USB
  2. Identify the serial port (usually /dev/ttyUSB0 on Linux or /dev/tty.usbserial-* on macOS)
  3. Ensure you have proper permissions to access the serial port:
# On Linux, add your user to the dialout group
sudo usermod -a -G dialout $USER
# Log out and back in for changes to take effect

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Software Requirements

The SO-101 robot is included in the LeRobot installation: 
pip install lerobot

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Configuration

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Basic Configuration

Create a configuration for your SO-101: 
from lerobot.robots.so_follower import SOFollowerRobotConfig
from lerobot.cameras.opencv import OpenCVCameraConfig

config = SOFollowerRobotConfig(
    robot_type="so101_follower",
    id="so101_main",
    port="/dev/ttyUSB0",
    cameras={
        "top": OpenCVCameraConfig(
            index_or_path=0,
            fps=30,
            width=640,
            height=480
        )
    }
)

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Configuration Parameters

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port
str
required
Serial port to connect to the arm (e.g., /dev/ttyUSB0)
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id
str
Robot identifier for calibration file management
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disable_torque_on_disconnect
bool
default:"true"
Whether to disable motor torque when disconnecting
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max_relative_target
float | dict[str, float]
Limit the magnitude of relative position changes for safety. Can be a single value for all motors or a dictionary mapping motor names to individual limits.
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cameras
dict[str, CameraConfig]
Dictionary of camera configurations
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use_degrees
bool
default:"true"
Use degree normalization instead of range[-100, 100]. Set to True for backward compatibility with existing datasets.
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calibration_dir
Path
Directory to store calibration files (defaults to ~/.cache/lerobot/calibration/robots/so_follower)

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Usage

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Basic Connection

from lerobot.robots.so_follower import SOFollower
from lerobot.robots.so_follower import SOFollowerRobotConfig

# Create configuration
config = SOFollowerRobotConfig(
    robot_type="so101_follower",
    id="so101_main",
    port="/dev/ttyUSB0"
)

# Connect to robot (context manager auto-disconnects)
with SOFollower(config) as robot:
    # Get current state
    obs = robot.get_observation()
    print(f"Current positions: {obs}")
    
    # Send action
    action = {
        "shoulder_pan.pos": 0.0,
        "shoulder_lift.pos": -45.0,
        "elbow_flex.pos": 90.0,
        "wrist_flex.pos": 0.0,
        "wrist_roll.pos": 0.0,
        "gripper.pos": 50.0
    }
    robot.send_action(action)

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Calibration

The SO-101 requires calibration before first use: 
robot = SOFollower(config)
robot.connect(calibrate=True)

# Follow the prompts:
# 1. Move the arm to the middle of its range of motion
# 2. Press ENTER
# 3. Move each joint through its full range
# 4. Press ENTER when done

# Calibration is saved to: ~/.cache/lerobot/calibration/robots/so_follower/{id}.json
Calibration data is saved per robot ID. If you have multiple SO-101 arms, use different IDs for each.

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Observation Format

The get_observation() method returns a dictionary: 
{
    # Motor positions (in degrees or normalized range)
    "shoulder_pan.pos": 0.0,
    "shoulder_lift.pos": -45.0,
    "elbow_flex.pos": 90.0,
    "wrist_flex.pos": 0.0,
    "wrist_roll.pos": 0.0,
    "gripper.pos": 50.0,
    
    # Camera images (if configured)
    "top": np.ndarray  # shape: (height, width, 3)
}

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Action Format

Actions follow the same structure as observations: 
action = {
    "shoulder_pan.pos": 10.0,   # degrees (if use_degrees=True)
    "shoulder_lift.pos": -30.0,
    "elbow_flex.pos": 60.0,
    "wrist_flex.pos": -15.0,
    "wrist_roll.pos": 0.0,
    "gripper.pos": 75.0  # 0=open, 100=closed
}

robot.send_action(action)

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Safety Features

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Maximum Relative Target

Limit how much motors can move in a single action: 
config = SOFollowerRobotConfig(
    port="/dev/ttyUSB0",
    # Limit all motors to 10 degrees per action
    max_relative_target=10.0
)

# Or set individual limits per motor
config = SOFollowerRobotConfig(
    port="/dev/ttyUSB0",
    max_relative_target={
        "shoulder_pan": 15.0,
        "shoulder_lift": 10.0,
        "elbow_flex": 20.0,
        "wrist_flex": 15.0,
        "wrist_roll": 30.0,
        "gripper": 25.0
    }
)

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PID Tuning

The SO-101 configures motors with conservative PID values to prevent shakiness:
  • P Coefficient: 16 (default is 32)
  • I Coefficient: 0
  • D Coefficient: 32
For the gripper specifically:
  • Max Torque Limit: 500 (50% to prevent burnout)
  • Protection Current: 250 (50% to prevent burnout)
  • Overload Torque: 25 (25% when overloaded)
These are set automatically in robot.configure() at /home/daytona/workspace/source/src/lerobot/robots/so_follower/so_follower.py:155.

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Motor Setup

If you need to assign motor IDs (for a new arm or replacement motors): 
robot = SOFollower(config)
robot.connect(calibrate=False)
robot.setup_motors()

# Follow the prompts to connect each motor individually
# Motors will be assigned IDs 1-6 in the order:
# gripper (6) -> wrist_roll (5) -> wrist_flex (4) -> 
# elbow_flex (3) -> shoulder_lift (2) -> shoulder_pan (1)

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Teleoperation

The SO-101 is commonly used in leader-follower setups: 
from lerobot.robots.so_follower import SOFollower, SOFollowerRobotConfig

# Leader arm (records human input)
leader_config = SOFollowerRobotConfig(
    robot_type="so101_follower",
    id="leader",
    port="/dev/ttyUSB0"
)

# Follower arm (executes actions)
follower_config = SOFollowerRobotConfig(
    robot_type="so101_follower",
    id="follower",
    port="/dev/ttyUSB1",
    max_relative_target=10.0  # Safety limit
)

with SOFollower(leader_config) as leader, \
     SOFollower(follower_config) as follower:
    while True:
        # Read leader position
        obs = leader.get_observation()
        
        # Mirror to follower
        action = {k: v for k, v in obs.items() if k.endswith(".pos")}
        follower.send_action(action)

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Troubleshooting

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Port Permission Denied

# Add user to dialout group
sudo usermod -a -G dialout $USER
# Log out and back in

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Robot Not Responding

  1. Check cable connections
  2. Verify the correct port is specified
  3. Try reconnecting the USB cable
  4. Check motor power supply

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Calibration Issues

# Force recalibration
robot.connect(calibrate=False)
robot.calibrate()  # Will prompt to run new calibration

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Motor Shaking

If motors are shaking or oscillating, the PID values may need adjustment. See the source code at /home/daytona/workspace/source/src/lerobot/robots/so_follower/so_follower.py:155 for the configuration method.

SO-100

Compact version of the SO series

Recording Data

Record demonstrations with SO-101

Teleoperation

Set up leader-follower control

Feetech Motors

Motor bus API reference

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