CLN closed-loop NEMA drivers: open hardware with encoder feedback on the board

Closed-loop feedback as the reason to exist

The CLN series is described in the README as an open-source project aimed at creating a range of compact, cost-efficient, high-performance closed-loop stepper drivers for various NEMA form factor motors. The stated goals are silent and smooth motion, high-precision position control and energy saving.

The mechanism that makes closed-loop different is the encoder. The feature list puts it first: the driver integrates an encoder for real-time position monitoring, which is what ensures precise and safe motion. A stepper motor is open-loop by nature, it follows commanded steps and silently loses them when it is overloaded. Adding an encoder turns that failure into a detected error.

The position claim is specific. The README states a position control accuracy of 0.01 degrees, and the CLN17 V3.0 specification lists 21 bit position feedback, which is what a closed-loop driver reports back about the shaft.

The application list is broad and worth reading as a scope statement rather than a promise: learning platforms, CNC machines and 3D printers, robotics and automation systems, collaborative robots, camera and telescope stabilisation, laboratory equipment, industrial motion control, and haptics and force feedback systems.

The audience is a maker or a small engineering team who wants closed-loop behaviour with a stepper and would rather not design the driver board from scratch.

A repository of hardware, not firmware

The repository layout is worth understanding before you clone anything. There are two directories that matter. The wiki directory holds design documentation, and the hardware directory contains design source files, manufacturing files, schematics, block diagrams and 3D models.

There is no source directory for firmware in this repository. The README points to two external options instead. CLN-SimpleFOC is described as SimpleFOC based firmware for CLN, described as pretty stable and ready to use, hosted in a separate repository. TunePulse is described as firmware for CLN and RadiX motor drivers, currently a work in progress with an estimated release date still to be determined.

So the split is: this repository tells you how to build the board, and somewhere else tells you how to make it move. That is a reasonable arrangement for open hardware, and it keeps the mechanical and electrical design files free of build system churn. It also means an evaluation has two parts, and the firmware half is where the schedule risk sits.

For the modular drivers aimed at embedded systems, the README sends you to the RadiX project repository instead, so the CLN family is one branch of a broader product line rather than a closed set.

Interfaces: STEP-DIR-EN, USB, CAN-FD, USART, I2C, SPI and ABZ

The CLN17 V3.0 is listed as the active version, described as the newest version with the best performance and BLDC support, with a specification document in the wiki. The key specs are given inline: discrete MOSFET based, 6 to 48V, 3.2A RMS and 4.5A peak, up to 60W output power, 21 bit position feedback, and a dual-sided SMD only assembly.

The supported interfaces list is what makes the board usable in an existing machine. STEP-DIR-EN is the familiar step and direction input that lets the driver stand in for a plain stepper driver. Beyond that come USB, CAN-FD, USART, I2C, SPI and ABZ, which is the incremental encoder output format.

That spread is a real design decision. STEP-DIR-EN means drop-in compatibility with existing CNC and 3D printer boards, while CAN-FD means several axes can be put on one bus, and USB means configuration and monitoring from a host. The supported motor list includes stepper and 3 phase BLDC or PMSM, so the same board covers a closed-loop stepper and a brushless axis.

The assembly note, dual-sided SMD only, matters to anyone planning to hand-build. V3.0 as described is a surface mount assembly.

Version history with obsolete and NRFND markers

The hardware directory carries several revisions of the CLN17, and the README is careful about which to use. CLN17 V1.0 is marked OBSOLETE and described as the pilot version. CLN17 V1.5 is also OBSOLETE, a cost-efficient version. CLN17 V2.0 is marked NRFND, a high voltage version, and V2.1 is an improved version of that line. CLN17 V2.5 is NRFND, described as having been meant to be the final version but to be skipped.

The README states plainly that obsolete designs will not be supported in future. That is a genuine warning for anyone who bought a CLN17 V1.0 from a group buy two years ago and is now planning a second unit: the board will keep working, but firmware fixes and new features will land on V3.0.

For the larger frame, the CLN234 V1 is listed as under tests, described as powerful and versatile, with external MOSFETs, 8 to 75V, 10A RMS and 20A peak, up to 1000W output power, 21 bit position feedback, and a 56x38x18mm size that fits inside a 60mm diameter mount. Its status as under tests is the deciding factor for an adoption decision rather than its specification.

Every version also links to its own specification document under the wiki, which is where the electrical and mechanical details live.

The non-commercial licence and what it rules out

The licence field for this repository is listed as Other, a custom licence GitHub cannot classify, and the README links a license.md file at the root. The badge on that file names the terms: CC BY-NC-SA 4.0.

The NC in that identifier is the part that matters for an engineering team. Creative Commons Attribution NonCommercial ShareAlike permits you to copy, modify and redistribute the design files provided the use is non-commercial and derivatives keep the same licence. A company building a machine it sells, or integrating a CLN board into a product, is commercial use, and the licence does not grant that.

The share-alike requirement compounds it. Modified hardware designs derived from these files have to be released under the same terms.

This is a common pattern for open hardware that is funded by sales of finished modules, and it is a perfectly coherent choice by the author. But it is a hard boundary on adoption, and it is worth being blunt about it: a company that wants to build CLN into a commercial machine needs a different arrangement, and that conversation, not a technical one, is what decides the project.

The repository also carries a sponsors.md file and a Discord community badge, plus Ko-fi and Patreon links, so the project is funded partly by its community.

Where the documentation stops

The README is explicit that it will be updated to reflect the latest progress and changes in the project, which reads as an acknowledgement that the front page is a status board rather than a manual.

Several things a buyer would want are not on it. There is no bill of materials, no assembly instruction document and no bring-up procedure in the repository listing; the wiki directory is said to contain design documentation, and each version links a specification document, but the README does not enumerate what those documents cover. There is no stated stepper motor size list beyond the NEMA 17 and NEMA 23 and 34 frames, no guidance on encoder selection for a given motor, and no statement of which firmware version pairs with which hardware revision.

There is also no list of GitHub releases, so there is no versioned artefact to reference, and the last push was on 2026-09-03.

The practical reading is that this is a hardware project delivered through a wiki and a Discord rather than through a documentation set you can consume offline, and that a first-time buyer should budget time for the community channel, not just for the parts.

Editorial conclusion

CLN is worth adopting if you are building a motion system where a stepper's lost steps would cost you more than a closed-loop driver, and you are willing to source parts and assemble the board yourself, since the value is the published design. It is the wrong tool for a commercial product you intend to sell, because the licence file is CC BY-NC-SA 4.0 and therefore non-commercial, and it is the wrong tool if you need firmware support today, since the SimpleFOC option is a separate repository and TunePulse is described as a work in progress with no release date. Before you commit, read wiki/CLN17/V3.0/specification.md, pick the firmware repository you will actually build, and confirm the CLN17 V3.0 supply chain, since the earlier V1 and V2 revisions are marked obsolete or not recommended for new designs.

Frequently asked questions

Official sources

1. creapunk/CLN-ClosedLoopNemaDriver on GitHub
2. Issues
3. Project website
4. README