Designed for the Millennium Machines Milo CNC toolchanger, and any RepRapFirmware or Klipper machine that needs a compact CAN-FD motor driver. The Ultralight N17 is a NEMA17 backpack stepper driver: it mounts on the back of your motor, communicates over CAN-FD, and drives a single bipolar stepper. It exposes an endstop input (3-pin PH 2.0) and an auxiliary output for a fan or similar device (2-pin PH 2.0).

Built in collaboration with Millennium Machines (makers of the Milo CNC and MillenniumOS). If you are running a Milo v1.5 or v2.0 with a BTT Scylla, the N17 is the companion board for a 5th-axis toolchanger or rotary axis without consuming a mainboard axis.

Tech Specs

• RP2350A MCU
• TMC2240 Motor Driver, 3A 36V Max*
• MCP2518 CAN-FD Controller (SPI) or direct Transceiver (MCP2542) connection to MCU
• Voltage selectable Endstop input and Aux output
• Select from VIN, 12V or 5V, shared across Endstop and Aux**
• Safe input range ~14V to ~32V
• 20-pin expansion header includes 4 x GPIO, TMC2240 A, B, N encoder pins and VIN, 12V, 5V and 3.3V

* 36V is the absolute max voltage the TMC2240 can tolerate.

** DO NOT drive low-voltage, high-current devices like a 5V servo from the Aux port. High inrush current may brown-out the chosen voltage rail and cause instability - this is particularly important on the 5V rail as it drives the CAN circuitry. Ideally, use VIN for everything :)

Your INPUT voltage needs to be below this so there is enough headroom for back-EMF from the motor to be dissipated in the event of a sudden stop, without causing an overvoltage event. There is a 2 watt 'braking' resistor mounted on the board that is switched on during overvoltage events, and will dump power as heat until the voltage drops below 36V. Behaviour at these extremes is unpredictable so do NOT rely on it.

What's in the box?

• 1 x Mettle & Byte Ultralight N17 R1.5, fully assembled (no soldering required)
• 1 x 70mm Motor Cable XH 2.5 to PH 2.0 (crimped without connector installed)
• 1 x PH 2.0 connector, 6 pin
• 1 x PH 2.0 connector, 4 pin
• 1 x PH 2.0 connector, 3 pin
• 1 x PH 2.0 connector, 2 pin
• 1 x XH 2.5 connector, 4 pin
• 5 x Jumpers, 2.0 pitch, 2 pin
• 10 x PH 2.0 crimps

What isn't in the box?

• NEMA17 Motor
• 3D Printed Fan and PCB mount
• Physical documentation. Refer to our product page
• Anything else un-listed

What else do you need?

For each Ultralight N17, you will need:

• 1 x NEMA17 4 wire, bipolar stepper motor
• 1 x XT30 2+2 cable
• 1 x Optional 3010 Fan, matching your chosen IO voltage
• 1 x Optional 3D-printed PCB Mount
• 1 x Optional 3D-printed Open Frame Fan Mount

Pinout

Why Ultralight N17?

As part of my work on the Millennium Machines team, I needed to drive a turret-style toolchanger on a Milo CNC while keeping all four axes of the BTT Scylla available for XYZ and A-axis motion. A backpack-style driver that mounted directly on the NEMA17 motor seemed like the right answer.

Nothing available did what I needed. The options I looked at were designed for 3D printer extruder toolheads, lacked RepRapFirmware support, or used a UART-only motor driver. So I built one.

What makes it special?

There is no other NEMA17 backpack motor driver that supports CAN-FD with both RepRapFirmware and Klipper. The Ultralight N17 is the only one.

Here is how it compares to the main alternatives:

The Ultralight N17 is designed to do a few things well:

• Drive a NEMA17 motor reliably, powerfully, and quietly
• Expose just enough IO for an extra axis: endstop input and auxiliary output
• Support three configurable IO voltages (VIN, 12V, 5V)
• Be simple to wire, flash, update, and use
• Stay open: open-source schematics, broken-out debug headers, expansion connector

The TMC2240 communicates over SPI like its bigger siblings (TMC2160, TMC5160), but integrates the H-bridge, so no external FETs are needed. The RP2350A provides the compute headroom for clean motion profiles. Together they make a capable driver in a compact package.

Open-loop as shipped. The 20-pin expansion header exposes the encoder pins for an AS5047P encoder daughter board. Closed-loop firmware is in active development via UltraFoCced, an open-source SimpleFOC-based project, and RRF expansion firmware support for closing the loop is also WIP.

The hardware supports it; the firmware is not yet complete and no timeline is guaranteed. If you need closed-loop control today, the Ultralight N17 is not the right board yet.

For Klipper users: the board defaults to UART mode and is Klipper-compatible. You can also write custom firmware using the RP2350's USB mass storage mode and the pico-sdk.

Why Mettle & Byte?

I have always wanted an excuse to design and build hardware, and this was it.

Mettle & Byte is a one-person operation, and the Ultralight N17 is what I hope will be the start of something. I self-funded the prototype runs and the first production run. At these scales, PCB production and assembly is not cheap. By buying from me you are directly supporting further development on Mettle & Byte hardware, as well as Millennium Machines software, and the broader goal of open, accessible CNC milling.

I am not in this to make a bundle. I am in this to make things that are genuinely useful, while supporting myself enough to keep exploring new hardware and software ideas and to look after the people who trust me with their machines.

Support

A full manual is maintained on the Mettle & Byte website, with up-to-date pinouts and configuration instructions.

Mettle & Byte is one person. I provide best-effort support on the Millennium Machines Discord, and other community members often help out too. You can also email help at mnb dot ltd.

If shipping rates are not available for your country, please contact me directly via Lectronz, and I will try and set shipping up for you as soon as I can.

I will add delivery services on an ad-hoc basis as requests are made. It may take me some time to find all the suitable rates for a destination, so if you make a request and I add a shipping rate and it is too expensive, please message me and I will see what I can do.

I am happy to ship almost anywhere, but do need to look into rates for your particular destination before I can offer it on a wider basis.

If you are ordering multiple boards at once, I would strongly suggest asking for a tracked and insured service with a courier like DHL Express, and I am happy to set this up on request.