Assemble SO-101

In the steps below we explain how to assemble our flagship robot, the SO-101.

Source the parts

Follow this README. It contains the bill of materials, with a link to source the parts, as well as the instructions to 3D print the parts, and advice if it’s your first time printing or if you don’t own a 3D printer.

Before assembling, you will first need to configure your motors. To this end, we provide a nice script, so let’s first install LeRobot. After configuration, we will also guide you through assembly.

Install LeRobot

To install LeRobot follow our Installation Guide

Configure motors

To configure the motors designate one bus servo adapter and 6 motors for your leader arm, and similarly the other bus servo adapter and 6 motors for the follower arm. It’s convenient to label them and write on each motor if it’s for the follower F or for the leader L and it’s ID from 1 to 6.

You now should plug the 5V or 12V power supply to the motor bus. 5V for the STS3215 7.4V motors and 12V for the STS3215 12V motors. Note that the leader arm always uses the 7.4V motors, so watch out that you plug in the right power supply if you have 12V and 7.4V motors, otherwise you might burn your motors! Now, connect the motor bus to your computer via USB. Note that the USB doesn’t provide any power, and both the power supply and USB have to be plugged in.

Find the USB ports associated to each arm

To find the port for each bus servo adapter, run this script:

python lerobot/scripts/find_motors_bus_port.py
Example outputs of script
Mac
Linux

Example output leader arm’s port: /dev/tty.usbmodem575E0031751

Finding all available ports for the MotorBus.
['/dev/tty.usbmodem575E0032081', '/dev/tty.usbmodem575E0031751']
Remove the usb cable from your MotorsBus and press Enter when done.

[...Disconnect leader arm and press Enter...]

The port of this MotorsBus is /dev/tty.usbmodem575E0031751
Reconnect the usb cable.

Example output follower arm port: /dev/tty.usbmodem575E0032081

Finding all available ports for the MotorBus.
['/dev/tty.usbmodem575E0032081', '/dev/tty.usbmodem575E0031751']
Remove the usb cable from your MotorsBus and press Enter when done.

[...Disconnect follower arm and press Enter...]

The port of this MotorsBus is /dev/tty.usbmodem575E0032081
Reconnect the usb cable.

Update config file

Now that you have your ports, update the port default values of SO101RobotConfig. You will find something like, update the port values with your actual motor ports:

@RobotConfig.register_subclass("so101")
@dataclass
class So101RobotConfig(ManipulatorRobotConfig):
    calibration_dir: str = ".cache/calibration/so101"
    # `max_relative_target` limits the magnitude of the relative positional target vector for safety purposes.
    # Set this to a positive scalar to have the same value for all motors, or a list that is the same length as
    # the number of motors in your follower arms.
    max_relative_target: int | None = None

    leader_arms: dict[str, MotorsBusConfig] = field(
        default_factory=lambda: {
            "main": FeetechMotorsBusConfig(
                port="/dev/tty.usbmodem58760431091",  <-- UPDATE HERE
                motors={
                    # name: (index, model)
                    "shoulder_pan": [1, "sts3215"],
                    "shoulder_lift": [2, "sts3215"],
                    "elbow_flex": [3, "sts3215"],
                    "wrist_flex": [4, "sts3215"],
                    "wrist_roll": [5, "sts3215"],
                    "gripper": [6, "sts3215"],
                },
            ),
        }
    )

    follower_arms: dict[str, MotorsBusConfig] = field(
        default_factory=lambda: {
            "main": FeetechMotorsBusConfig(
                port="/dev/tty.usbmodem585A0076891",  <-- UPDATE HERE
                motors={
                    # name: (index, model)
                    "shoulder_pan": [1, "sts3215"],
                    "shoulder_lift": [2, "sts3215"],
                    "elbow_flex": [3, "sts3215"],
                    "wrist_flex": [4, "sts3215"],
                    "wrist_roll": [5, "sts3215"],
                    "gripper": [6, "sts3215"],
                },
            ),
        }
    )

Here is a video of the process:

Step-by-Step Assembly Instructions

The follower arm uses 6x STS3215 motors with 1/345 gearing. The leader however uses three differently geared motors to make sure it can both sustain its own weight and it can be moved without requiring much force. Which motor is needed for which joint is shown in table below.

Leader-Arm Axis Motor Gear Ratio
Base / Shoulder Yaw 1 1 / 191
Shoulder Pitch 2 1 / 345
Elbow 3 1 / 191
Wrist Roll 4 1 / 147
Wrist Pitch 5 1 / 147
Gripper 6 1 / 147

Set motor IDs

Plug your motor in one of the two ports of the motor bus and run this script to set its ID to 1. Replace the text after —port to the corresponding control board port.

python lerobot/scripts/configure_motor.py \
  --port /dev/tty.usbmodem58760432961 \
  --brand feetech \
  --model sts3215 \
  --baudrate 1000000 \
  --ID 1

Then unplug your motor and plug the second motor and set its ID to 2.

python lerobot/scripts/configure_motor.py \
  --port /dev/tty.usbmodem58760432961 \
  --brand feetech \
  --model sts3215 \
  --baudrate 1000000 \
  --ID 2

Redo this process for all your motors until ID 6. Do the same for the 6 motors of the leader arm, but make sure to change the power supply if you use motors with different voltage and make sure you give the right ID to the right motor according to the table above.

Here is a video of the process:

Clean Parts

Remove all support material from the 3D-printed parts, the easiest wat to do this is using a small screwdriver to get underneath the support material.

Joint 1

Joint 2

Joint 3

Joint 4

Joint 5

Gripper / Handle

Follower
Leader
Wiring

Calibrate

Next, you’ll need to calibrate your SO-101 robot to ensure that the leader and follower arms have the same position values when they are in the same physical position. The calibration process is very important because it allows a neural network trained on one SO-101 robot to work on another.

Manual calibration of follower arm

You will need to move the follower arm to these positions sequentially, note that the rotated position is on the right side of the robot and you have to open the gripper fully.

1. Middle position 2. Zero position 3. Rotated position 4. Rest position
SO-101 leader arm middle position SO-101 leader arm zero position SO-101 leader arm rotated position SO-101 leader arm rest position

Make sure both arms are connected and run this script to launch manual calibration:

python lerobot/scripts/control_robot.py \
  --robot.type=so101 \
  --robot.cameras='{}' \
  --control.type=calibrate \
  --control.arms='["main_follower"]'

Manual calibration of leader arm

You will also need to move the leader arm to these positions sequentially:

1. Middle position 2. Zero position 3. Rotated position 4. Rest position
SO-101 leader arm middle position SO-101 leader arm zero position SO-101 leader arm rotated position SO-101 leader arm rest position

Run this script to launch manual calibration:

python lerobot/scripts/control_robot.py \
  --robot.type=so101 \
  --robot.cameras='{}' \
  --control.type=calibrate \
  --control.arms='["main_leader"]'

Congrats 🎉, your robot is all set to learn a task on its own. Start training it by following this tutorial: Getting started with real-world robots

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