servomotor-mcp

Drive open-source Gearotons M17 servomotors from natural language.

An MCP server that exposes the M17 — a NEMA-17 integrated, closed-loop, RS-485 servomotor — to Claude Desktop, Claude Code, or any MCP client. Control real motors by just asking:

"Find my motors and rotate the one on the bench two full turns, slowly."

Nothing is hardcoded: the server discovers your serial ports, auto-detects the motors on the bus (the firmware's "Detect devices" command), and exposes the entire firmware command set — every command in the servomotor library's catalog becomes an MCP tool automatically (48 commands as of library 0.10.0), plus a few high-level tools for everyday moves. It ships with a mock backend, so you can try the whole thing with no hardware.

▶ 50-second video: the real motor and this session side by side — recorded 2026-09-09 on a bench M17; every line above is from the session log.

Step-by-step tutorial (boxed motor to "talk to it" in about twenty minutes): Talk to a servomotor from Claude Code on Hackster.

The first servomotor with an official MCP server. Open hardware, open firmware, open software — and now an open, AI-native control interface.

Quickstart (no hardware, ~2 minutes)

# Run the server directly with uv (recommended). This runs the SIMULATOR —
# for real motors see "Drive real motors" below:
uvx --from servomotor-mcp servomotor-mcp

# or install it:
pip install servomotor-mcp
servomotor-mcp

Then add it to Claude Desktop — copy the block from examples/claude_desktop_config.json into your claude_desktop_config.json, restart Claude Desktop, and ask: "What serial ports do you see? Connect and find my motors." See examples/demo_prompts.md for a scripted demo.

Drive real motors

Plug an M17 (or a daisy-chain of them) into a USB↔RS-485 adapter and install the [serial] extra — that's it, no configuration:

pip install 'servomotor-mcp[serial]'   # pulls in the Gearotons servomotor library
servomotor-mcp

With the servomotor library installed the server uses the real serial backend automatically. Without it, the server runs its simulator and says so: list_serial_ports and connect return a notice field, and a warning goes to stderr. With uv, use uvx --from 'servomotor-mcp[serial]' servomotor-mcp. In a session, the model then:

1. list_serial_ports — enumerates the machine's ports (macOS /dev/cu.*, Windows COM*, Linux /dev/ttyUSB*), flagging USB serial adapters;
2. connect — opens the port you (or it) picked, at 230400 baud;
3. auto-detects every motor on that bus (unique ID + alias) — no address maps to write;
4. drives them. Tell it in plain English which adapter to use if you have several.

Tools

High-level (discovery + everyday motion):

Plus one tool per firmware command, generated from the library's command catalog: enable_mosfets, go_to_position, move_with_velocity, move_with_acceleration, multimove, homing, zero_position, get_position, get_temperature, set_device_alias, set_pid_constants, system_reset, vibrate, ping, … — anything the motor can do, the model can do. Motors are addressed by their alias number, their 16-hex-digit unique ID, or "all" (broadcast). Values are in friendly units (degrees, seconds, degrees/s, volts, °C); the server converts to firmware units.

How it works

natural language → Claude → MCP tool calls → this server → RS-485 → M17 motors

The server is a thin layer over the Gearotons servomotor Python library. The library is data-driven — motor_commands.json defines every firmware command — and the server turns that same catalog into MCP tools, so new library commands appear automatically. Tool calls are forwarded straight to the hardware — no software clamping; full multi-turn travel, any speed. The motor's own firmware protections (over-current / over-voltage / over-temperature) still apply. The same tools run against the mock backend (GEAROTONS_MOTOR_BACKEND=mock) for development and CI.

Environment variables (all optional):

• GEAROTONS_MOTOR_BACKEND — auto (default: serial when the servomotor library is installed, else mock), serial, or mock.
• GEAROTONS_SERIAL_PORT — default port for connect when the model doesn't pass one.
• GEAROTONS_DEFAULT_SPEED_DPS — default speed for move_to/move_relative (180).

Develop / test

pip install -e '.[dev]'
GEAROTONS_MOTOR_BACKEND=mock pytest     # catalog + mock-bus + server-tool tests

hardware_tests/ contains scripts that exercise the real serial path end to end (port sweep, full command suite, stdio MCP session) against a bench motor.

Status

• ✅ Full firmware command surface (48 commands), serial-port discovery, bus auto-detection — verified on a physical M17 (fw 0.15.3.0) over a real stdio MCP session and via uvx, on all four test adapters (motor found only where it truly is).
• ✅ Mock backend + 39 unit tests, no hardware needed.
• ✅ Cross-platform port handling (macOS / Windows / Linux) via pyserial enumeration.

License

MIT. Hardware, firmware, and software for the M17 are open-source — see github.com/tomrodinger/servomotor.