A tiny, 3D-printable, open-source robotic arm project inspired by the SO-ARM100 by TheRobotStudio. Designed for LeRobot compatibility and based on the Seeed Studio XIAO ecosystem.
This project consists of two replica arms:
- Follower Arm: 6-DOF (5 Revolute + 1 Gripper) with a 24cm reach (12cm + 12cm) optimized for 50g payload capacity using MG90S/EMAX servos.
- Leader Arm: A passive replica used for teleoperation, featuring a spring-loaded trigger to measure grip intensity.
- Upper Arm (L1): 12.0 cm
- Forearm (L2): 12.0 cm
- Total Reach: 24.0 cm
To handle the high torque demands at full 24cm extension with a 50g payload, a shoulder helper spring (or strong rubber band) is required to reduce servo stress.
- Design Goal: The spring should passively hold the arm at ~45° when unpowered.
-
Target Stiffness:
$k \approx 0.14 Nm/rad$ . - Servo Load Reduction: 70% (Peak torque drops from 0.17 Nm to 0.05 Nm).
- CAD Implementation: Ensure anchor points are included on the Base and Shoulder (J2) blocks for mounting an extension spring.
- Controller: Seeed Studio XIAO ESP32S3 Sense (Follower) / XIAO ESP32-C3 (Leader).
- Servo Driver: Adafruit 16-Channel 12-bit PWM/Servo Driver - PCA9685.
- Servos: EMAX ES08MA II (12g, Metal Gear) or MG90S (Budget).
- Camera: OV2640 2MP (included with XIAO Sense).
- Communication: I2C (SDA/SCL) from XIAO to PCA9685.
The servos (EMAX ES08MA II / MG90S) are rated for a strict 4.8V to 6.0V range.
- Optimal Performance: Running the system at exactly 6.0V increases the stall torque from ~0.18 Nm to 0.22 Nm compared to a 5V supply.
- Warning: Do NOT provide raw 7.4V (2S LiPo) to the servos or PCA9685. You must use a High-Current 6V Step-Down Converter (Buck/BEC) that can handle at least 3A continuous (since each servo can draft ~850mA at stall).
| Component | Mid (EMAX ES08MA II) | Budget (MG90S) |
|---|---|---|
| Servos / Pots | $60.00 | $45.00 |
| MCUs (S3 + C3) | $28.00 | $28.00 |
| Adafruit PCA9685 | $15.00 | $15.00 |
| Trigger (FSR/Pot) | $10.00 | $10.00 |
| Battery & Power | $24.00 | $24.00 |
| Filament & Misc | $20.00 | $20.00 |
| Total Est. | ~$172.00 | ~$157.00 |
- Editor: OnShape (Open Source Project).
- CAD Guidelines: CAD Design Guidelines
- Deliverables:
STL: Ready for 3D printing.STEP: For assembly and modification.URDF: For ROS / Simulation.MJC: MuJoCo XML for LeRobot training.
To prevent breakage of the fragile OV2640 FPC cable:
- Strategy: The XIAO ESP32S3 Sense is mounted directly on the follower's forearm. This keeps the camera cable static, only moving the robust power and data wires across the arm joints.
- Print the parts from the
stl/directory. - Assemble using M2 and M3 screws.
- Flash the ESP32 firmware in
firmware/. - Connect to LeRobot via USB Serial.
This project is open-source and part of the LeRobot ecosystem.