SO-ARM-chan: Fusing Stack-chan's Soul with LeRobot's Body

The Problem: Two Worlds, Wonderful but Apart

In the maker universe, two incredible communities thrive.

One is the world of "Stack-chan, " a super-kawaii robot that charms people with its rich emotional expressions. Here, anyone can build a little friend with a "soul."

The other is the world of "LeRobot SO-101, " where powerful robotic arms make advanced AI accessible to everyone. Here, cutting-edge technologies like imitation learning become tangible.

While both are vibrant, they represent a common divide in robotics: a gap between functional, task-oriented machines and relational, character-driven companions. A huge opportunity was being missed. What if we could bridge this gap and give Stack-chan's friendly "soul" to LeRobot's powerful "body"?

"SO-ARM-chan" is my answer to that question.

The Solution: SO-ARM-chan, a Bridge Between Worlds

SO-ARM-chan is more than just a robot arm; it's a new innovation platform where creativity, technology, character, and AI intersect.

Powered by the M5Stack AtomS3R as its brain, the robot comes to life. When you gently shake it, the onboard IMU detects changes in acceleration, causing its eyes on the screen to shift dynamically, as if looking around. Press a button, and it cycles through pre-programmed motion patterns like a polite bow or a playful head shake. Each servo moves at its own independent interval, creating complex, life-like, and non-synchronous gestures.

This is our attempt to breathe a soul into technology.

https://x.com/mityomi722/status/1958466537733730667

https://x.com/mityomi722/status/1958383338080878870

What Makes This Project Special?

The true value of SO-ARM-chan lies in the unique synergy created by combining the strengths of both worlds.

• Connectivity to AI from LeRobot:SO-ARM-chan opens the door to imitation learning and foundation models like NVIDIA's Isaac GR00T. It becomes an affordable and accessible hardware platform for hobbyists to experiment with cutting-edge AI research.
• Human-like Charm from Stack-chan:With IMU-linked expressions, unique motion patterns, and future LLM integration, the impersonal robot arm is elevated into a partner that users can form an emotional connection with.

This fusion creates a new category of "Character AI Robot"—a platform that is both technically advanced and affectionately engaging. Researchers gain an affordable and easily replicable platform to study Human-Robot Interaction (HRI) with character-driven agents. Hobbyists and students can finally democratize cutting-edge AI research, equipping their personal projects with technologies that were previously accessible only in high-end labs.

How It Works: The Technical Heart

SO-ARM-chan's core functions were designed with a focus on "responsiveness" and "robustness."

Hardware:

• The system is built around the M5Stack AtomS3R, a compact powerhouse with an integrated IMU, LCD, and powerful CPU. It controls six high-performance Feetech servos and is housed in custom 3D-printed parts. The design is highly expandable, ready to integrate a camera unit (AtomS3R-M12) and a voice unit (Atomic Echo Base).

Software:

• Autonomous Motion & Expression: The firmware, developed in PlatformIO, brings SO-ARM-chan to life. It continuously reads IMU data to create dynamic eye movements and runs multiple independent timers to control each servo's unique motion cycle. This architecture produces nuanced, asynchronous behaviors that feel organic.
• High-Performance BLE Teleoperation: A working proof-of-concept demonstrates wireless control via Bluetooth Low Energy, achieving smooth and precise remote operation with under 5ms of latency. This allows for real-time, intuitive control using a simple JSON-based command protocol.
• Robust Self-Contained Calibration: After a one-time calibration with LeRobot, all parameters (min/max limits, homing offset) are stored directly on each servo's internal EEPROM. SO-ARM-chan reads this data on startup, eliminating the need for external configuration files like follower_arm.json on a PC. This makes the robot truly standalone and ensures consistent, reliable performance every time.

How to Build It

You can bring SO-ARM-chan to life with your own hands. All you need are some basic tools and a little time.

• 3D Printing: Download and print the STL files for the face and mount.
• Assembly & Wiring: Follow the detailed guide to assemble the servos and electronics. No soldering required. A simple design that can be easily secured with two screws at the camera mount position. The AtomS3R is simply pushed in from the back.

• Software Setup: Use PlatformIO to flash the firmware and image files to the AtomS3R.

Demonstration

Words can only say so much. See SO-ARM-chan in action to understand how it moves, reacts, and can be controlled in this video.

Future Roadmap

This project is just the beginning. We have big plans to evolve the SO-ARM-chan platform.

• Voice Interaction: Integrate a microphone and speaker to enable natural conversations through Large Language Models (LLMs).
• Vision Capabilities: Add a camera to enable features like object recognition and face tracking.
• Full LeRobot Integration: Deepen the connection with LeRobot to allow for onboard data collection for imitation learning.

"In short, SO-ARM-chan is an open invitation to explore the future of robotics, where machines are not just tools, but partners."