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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 Zhihui Jun (peng-zhihui)

FULL CAD BOM FIRMWARE DOCS

RoboticsOpen-hardware

difficulty
●●●●●
time
weeks to months
license
license not specified
repo
repo ACTIVE15,282 stars

WHAT YOU’LL NEED

  • 3D printer + filament — printable parts — files are in the repo
  • Electronic parts — full list with part numbers in the repo BOM
  • Dev board / microcontroller — runs the project firmware
  • Soldering kit + basic tools — one-time buy, serves every future build

Partner

Reach your Pi from anywhere — Remote desktop to the machine running this build — no port forwarding, works right from the browser.Try Getscreen.me
Videos
1

COMPAREE VERDICT

This is a six-axis desktop robotic arm with harmonic-drive joints and a wireless teach pendant that tracks your hand in space. The arm mirrors your movements, and every design file — CAD models, PCBs, firmware for the custom stepper servo drivers — is on GitHub. 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 aluminum structural parts and commercial harmonic reducers, which alone will cost several hundred dollars if you can source them at all. The repo has no assembly manual, no license, and documentation that assumes you read circuit schematics fluently and can navigate Chinese-language CAD notes. If you have a machine shop, can fabricate precision metal parts, and are comfortable writing motor control firmware when the provided code does not quite fit your hardware, 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 teach pendant is clever — an IMU board transmits orientation data over 2.4 GHz and the arm solves inverse kinematics in real time — but you cannot substitute an Xbox controller or a phone without rewriting the whole input layer. The thing most likely to go wrong: ordering printed circuit boards and 3D-printed parts, then discovering halfway through that the arm depends on machined aluminum brackets and gearboxes you do not have access to.

NOT IN THE REPO

  • —3D models (STEP and STL), PCB Gerber files, and firmware for the servo drivers and teach pendant 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 aluminum parts and commercial harmonic reducers (e.g., HDUC-5-50 or equivalent), not 3D-printed gears.
  • —A bill of materials exists but is embedded in Chinese-language documentation and scattered across subdirectories.
  • —The wireless teach pendant uses a custom IMU board and STM32 firmware; you cannot swap in an off-the-shelf controller without rewriting the protocol.

Can I build this?

PrintStructural parts, motor mounts, and enclosures for the servo drivers and teach pendant. The repo includes STL files but the original design expects CNC aluminum for load-bearing joints.
BuySix stepper motors (NEMA 17 or equivalent), harmonic reducers (HDUC-5-50 or compatible, six units), PCBs for the servo drivers and teach pendant (Gerber files in repo), STM32 microcontrollers, IMU sensor (e.g., MPU6050 or MPU9250), 2.4 GHz wireless module, linear voltage regulators, motor driver ICs, bearings, fasteners, and aluminum stock 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 — six units can exceed $600 if bought new, and Chinese suppliers may have long lead times or require bulk orders. Stepper motors, PCBs, and aluminum stock add another $200–400. Total cost typically runs $800–1200 unless you already own reducers or salvage motors.
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. No mains voltage or lithium cells in the design as published.

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

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HeyGears G1: 10M+ colors and transparent parts in one print, plus UV printing on flat objects. Figures, parts and labels — no painting.

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Videos

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

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 and STL files are in the Hardware directory. Open them in CAD software to identify which parts are meant to be machined vs. printed.)
  2. 2.Source or fabricate the harmonic reducers and aluminum brackets(The design expects HDUC-5-50 or equivalent reducers. Check Chinese suppliers (Taobao, AliExpress) or consider ordering custom gearboxes. This is the longest lead time in the build.)
  3. 3.Order PCBs and components for the servo drivers(Gerber files are in the Electronics subdirectory. You will need to source STM32 microcontrollers, motor driver ICs, and passives from the schematic.)
  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.

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KNOWN ISSUES

  • The design expects commercial harmonic reducers, not 3D-printed cycloidal gears. If you cannot source or afford HDUC-5-50 units (or equivalent), the arm will not have the precision or load capacity shown in the demo.
  • There is no license file in the repository. Ask the creator before any commercial use or public derivative project.
  • The bill of materials is scattered across Chinese-language PDFs and directory READMEs. Budget time to inventory every component before ordering.
  • The teach pendant firmware is tightly coupled to a specific IMU and wireless module. Swapping hardware means rewriting the sensor fusion and communication protocol.
  • Motor tuning is not documented. Expect to spend time adjusting PID gains and acceleration limits to avoid oscillation or missed steps.
  • The repository was last updated in 2020. 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 creator used HDUC-5-50 or similar Chinese-made harmonic drives with a 1:50 reduction ratio. These are not standard off-the-shelf parts in most Western markets. Search Taobao or AliExpress for 'harmonic reducer HDUC' or contact robotics suppliers directly.

Is there a pre-compiled firmware binary?

No. The firmware is source code only, and you will need to set up the STM32 toolchain (e.g., STM32CubeIDE or PlatformIO) to compile and flash it. The repo includes a Makefile but no step-by-step build instructions.

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.

Community builds

No community builds yet — be the first, we feature the best ones.

Discussion1

FROM THE COMPAREE TEAM

Fifteen thousand stars, but no license and no assembly guide — just CAD files and firmware. Would you machine the aluminum parts yourself, or try to find a shop that will take the STEP files and give you a quote?

CompareeTEAM1mo agoedited

Practical notes from our verification: the repository has not been updated since late 2020, and the README is a mix of English and Chinese with no consolidated build log. The creator demo video confirms the teach pendant works as described, but there is no footage of the assembly process or a working bill of materials. The single biggest barrier is not the electronics — it is sourcing or fabricating the harmonic reducers and aluminum brackets, which are not standard hobbyist parts. If you have access to a machine shop or know a supplier for HDUC-5-50 reducers, this is an extraordinary reference design. If you are expecting to order everything from a maker electronics site, you will hit a wall before you even print the first part.

Zhihui Jun (peng-zhihui)

Zhihui Jun is an engineer and maker known for compact, high-performance robotics and electronics projects. He built Dummy-Robot to demonstrate precision desktop manipulation with off-the-shelf steppers and custom drive electronics. The project went viral on Chinese social media and GitHub, and has been referenced in academic papers on low-cost robotic arms.

GitHub

Star the project on GitHub

DISCLAIMER

  • Comparee is not the author of the projects featured here. All rights to each project belong to its creator — every page links to the original source, and we never host creators’ files.
  • 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.
  • Building and operating any project is at your own responsibility. Protective equipment, safe workshop practice and compliance with local regulations are the builder’s responsibility.
GitHub repo