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DUMMY-ROBOT — COMPACT 6-AXIS DESKTOP ROBOTIC ARM (15K STARS)

A desktop arm that mirrors your hand movements, with harmonic drives and custom servo drivers — every file public.

by Peng Zhihui (稚晖君)

FULL CAD BOM FIRMWARE DOCS

RoboticsOpen-hardware

Built withSTM323D printing

difficulty
●●●●●
time
weeks to months
license
license not specified
repo
repo ACTIVE15,595 stars

WHAT YOU’LL NEED

Videos
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COMPAREE VERDICT

This is a six-axis desktop robotic arm with harmonic-drive joints, closed-loop stepper drivers on a CAN bus, and a wireless handheld controller. Every main design file - STEP models, PCBs, firmware for the controller and the stepper drivers - is on GitHub, and fifteen thousand stars say people want to build it. The catch: this is an advanced machining and electronics project dressed as a desktop toy. The original build uses CNC aluminium structural parts and commercial harmonic reducers, which the creator bought second-hand for about 600 CNY each. The repo has no assembly manual, no licence, and a README in Chinese. If you have a machine shop, can fabricate precision metal parts, and are comfortable working in STM32 firmware, this is an extraordinary reference design. If you were hoping for a weekend kit, you will spend the first weekend just figuring out what to order. The firmware accepts commands over USB, UART and CAN and exposes an application layer, so other input devices are possible if you write the code. The thing most likely to go wrong: ordering PCBs and printed parts, then discovering halfway through that the arm depends on machined aluminium brackets and reducers you do not have access to.

GOOD TO KNOW

  • —3D models (STEP), PCB Gerber files, a pre-built stepper-driver HEX and firmware source for the controller and drivers are in the repo.
  • —No license file — the repo is public but there is no explicit permission for commercial use or derivative works.
  • —No build guide or assembly instructions — you are reading circuit diagrams and working from CAD files alone.
  • —The original design uses CNC aluminium parts and Harmonic-brand harmonic drive reducers, not 3D-printed gears.
  • —No standalone bill of materials; components have to be read from the Altium schematics and PCB files.
  • —The wireless controller (Peak) is a separate ESP32-based handheld in its own repository (a port of the X-Track project); using a different controller means writing your own interface to the arm's command protocol.

Parts to buy

9 items

From our check of the build. Exact quantities and part numbers are in the creator’s BOM.

  • Six stepper motorsFind
  • Six harmonic reducersFind
  • Stepper-driver PCBs (Gerbersfrom the repo files
  • REF controller boardFind
  • Separate Peak handheld controllerFind
  • STM32 partsFind
  • BearingsFind
  • FastenersFind
  • Aluminium if machining your own bracketsFind

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Can I build this?

PrintStructural parts, motor covers and enclosures can be exported from the STEP models in the repo, but the original design uses CNC aluminium for load-bearing joints.
BuySix stepper motors (size 42 / NEMA 17 for the larger joints, size 20 / NEMA 8 for the wrist), six harmonic reducers (or the creator's cycloidal alternative), stepper-driver PCBs (Gerbers in repo for the 42 driver; other boards as Altium projects), REF controller board, the separate Peak handheld controller, STM32 parts, bearings, fasteners, and aluminium if machining your own brackets.
Tools3D printer (if printing any parts), access to CNC milling or a machine shop for aluminum components, soldering station for PCB assembly, precision screwdrivers, hex keys, multimeter, oscilloscope (recommended for debugging motor drivers), STM32 programmer (ST-Link or compatible), and a 12–24V power supply (current depends on motor count and load).
SkillsAdvanced. You need to machine or source precision metal parts, assemble and debug custom motor driver boards, flash and tune STM32 firmware, and troubleshoot real-time inverse kinematics. Reading circuit diagrams and navigating repositories with minimal English documentation is required.
TimeWeeks to months, depending on whether you machine parts yourself or order them. PCB assembly and firmware bring-up alone can take a weekend per board if you hit bugs. First-time builders should expect at least a month of part-time work.
Cost$$$. Harmonic reducers dominate the cost: the creator paid about 600 CNY each for six second-hand units. Motors, PCBs, electronics and aluminium come on top. For comparison, his planned low-cost printed version with cycloidal reducers targeted under 2,000 CNY for the whole arm.
SafetyStandard electronics risks: verify power supply polarity before connecting motor drivers, and do not touch driver heatsinks under load. The arm has no built-in collision detection, so keep hands clear during motion.

Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.

Videos

Creator demo video showing the teach pendant in use and the arm mirroring hand movements. No assembly walkthrough or voiceover tutorial.

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Gallery

Start here

Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.

  1. 1.Read the repository README and locate the CAD files (The STEP models are in the 4.Model directory. Open them in CAD software to identify which parts are machined vs. printed.)
  2. 2.Source or fabricate the harmonic reducers and aluminum brackets(The original uses Harmonic-brand harmonic drive modules; the creator bought his second-hand for about 600 CNY each. For a cheaper, lower-precision route see his cycloidal reducer repo (peng-zhihui/CycloidAcuratorNano). This is usually the longest lead time in the build.)
  3. 3.Order PCBs and components for the servo drivers(Gerbers for the stepper driver are in 1.Hardware/MotorDriver-42/Gerber; the REF controller and other boards are Altium projects you export yourself. The 20 mm driver board is also Altium-only.)
  4. 4.Assemble and test one servo driver in isolation(Do not populate all six boards at once. Test one motor and driver pair, verify the firmware boots, and confirm you can command position before scaling up.)

Resources

Documentation, files and community threads for this build — we link straight to the original sources and never rehost the creator’s files.

KNOWN ISSUES

  • The original design uses Harmonic-brand harmonic drive modules, which the creator bought second-hand for about 600 CNY each. If you cannot source equivalent harmonic reducers, the arm will not match the precision or load capacity shown in the demo; the creator's cheaper cycloidal reducer is a separate, lower-precision route.
  • There is no license file in the repository. Ask the creator before any commercial use or public derivative project.
  • There is no standalone bill of materials. Parts must be pulled from the Altium schematics and the STEP models, so budget time to build your own BOM before ordering.
  • The handheld controller (Peak) is its own ESP32 project in a separate repository; if you want a different input device, you will need to send commands to the arm over USB, UART or CAN yourself.
  • Motor tuning is not documented. Expect to spend time adjusting PID gains and acceleration limits to avoid oscillation or missed steps.
  • The repository has not seen major updates since 2024 (README last revised February 2022). Some linked components may be discontinued or hard to source.

Can I print the structural parts instead of machining aluminum?

The joints and motor mounts in the original design are aluminum because they carry torque and need dimensional stability. You can try printing them in a strong filament like carbon-fiber nylon, but expect reduced precision and a higher chance of layer separation under load. The demo videos show a machined version.

What harmonic reducers does the design use?

The original uses Harmonic-brand harmonic drive modules that the creator bought second-hand for about 600 CNY each; the README works with a 30:1 reduction. For a cheaper route he published his own cycloidal reducer (peng-zhihui/CycloidAcuratorNano).

Is there a pre-compiled firmware binary?

For the stepper drivers, yes: a ready-to-flash HEX is in 2.Firmware/_Released HEX. The main REF controller firmware is source code (STM32 HAL, FreeRTOS) that you build with the STM32 toolchain.

Can I use this arm with ROS or other robot software?

Not out of the box. The firmware speaks a custom serial protocol for position commands. You would need to write a ROS driver or adapter layer to translate standard joint position messages into the format the arm expects.

Why is there no license file?

The repository is public but the creator did not include a LICENSE file. In most jurisdictions that means you can view and study the code, but you cannot legally redistribute, modify, or sell derivatives without explicit permission. Open an issue on GitHub or contact the creator if you need clarity.

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Discussion1

FROM THE COMPAREE TEAM

Fifteen thousand stars, but no licence and no step-by-step assembly guide, just STEP models, PCBs and firmware. Would you machine the aluminium parts yourself, or take the STEP files to a shop for a quote?

CompareeTEAM2mo agoedited

Practical notes from our verification: the repository was created in October 2021 and last pushed in March 2024; the README is in Chinese and the GitHub repo has no licence. It contains Altium PCB projects, firmware source plus a pre-compiled HEX for the stepper drivers, and STEP models (no STL files). The arm combines size-42 (NEMA 17) and size-20 (NEMA 8) steppers. The single biggest barrier is the reducers: the original uses Harmonic-brand harmonic drive modules, which the creator says he bought second-hand for about 600 CNY each, and he mentions a cheaper version with a self-designed cycloidal reducer as a future plan. If you have access to a machine shop or used harmonic drives, this is an extraordinary reference design; if you expect to order everything from a maker electronics site, you will hit a wall early. Correction (4 October 2026): we re-checked this page line by line against the project's own repository, documentation and videos, and fixed errors in earlier versions.

Peng Zhihui (稚晖君)

Zhihui Jun (稚晖君) is an engineer and maker known for compact robotics and electronics projects. He built Dummy-Robot as a compact six-axis arm with his own closed-loop stepper drivers and a CAN bus, documented it in a video, and published the CAD, PCBs and firmware on GitHub, where it has more than 15,000 stars.

GitHub

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  • Information is provided without warranty and may become outdated as projects evolve. Prices are indicative bands only — always check the creator’s parts list for current costs.
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