3D PRINT A ROBOT HAND THAT COPIES YOUR EVERY MOVE — IN A WEEKEND OF PRINTING
A 3D-printed robotic arm that mirrors your hand in real time — move the leader, the follower copies you.
by NormaCore
RoboticsOpen-hardware
- difficulty
- ●●●●○
- time
- a weekend-plus
- license
- MIT
- repo
- repo ACTIVE626 stars
●●●●○ · a weekend-plus · MIT · 626 stars · repo ACTIVE
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
COMPAREE VERDICT
ElRobot is a leader-follower robotic arm: you move one printed hand, the other mirrors it in real time over WiFi. Both arms are entirely 3D-printed PLA with off-the-shelf servos. 7+1 degrees of freedom, 430mm reach, 800g payload, about 28 hours of printing for the pair. The repository gives you STEP files, STL, a BOM, assembly instructions, firmware and a URDF. The single hardest part is not the printing — it is getting eight servos to behave identically when cheap clones vary wildly in torque and dead-band. The non-commercial licence means you cannot sell assembled units or offer it as a service without permission. If you want a weekend project that moves and grabs, this is one of the cleanest open designs available. If you need guaranteed servo performance or a permissive licence, it will disappoint.
IN THE REPO
NOT IN THE REPO
- —STEP and STL files for both leader and follower arms are in the repository.
- —BOM lists servos (MG90S, MG995, MG996R) and an ESP32-WROOM-32 board.
- —Firmware is provided; you flash the ESP32 and configure WiFi credentials.
- —Assembly guide and URDF model are included.
- —Licence is CC BY-NC-SA 4.0 — non-commercial use only, share-alike required.
- —No PCB design or custom electronics; you wire servos directly to the ESP32.
Can I build this?
Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.
Partner · KickstarterHeyGears G1: 10M+ colors and transparent parts in one print, plus UV printing on flat objects. Figures, parts and labels — no painting.
Gallery
Start here
Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.
- 1.Read the assembly guide in the docs/ folder to understand the build order. (Start with the BOM and print order — you need both arms and all brackets before assembly.)
- 2.Print the leader arm parts (7 STL files, ~14h) and follower arm parts (7 STL, ~14h).(Use PLA, 0.2mm layers, 20% infill. Some joints need supports. Print servo brackets (16 total) in a separate batch.)
- 3.Order servos and ESP32 from the BOM. Test each servo before installation.(Cheap MG90S clones vary in dead-band. If you can, buy from a supplier with reviews. Budget an extra $20 for replacements.)
- 4.Flash the ESP32 with the provided firmware and set WiFi credentials.(Use Arduino IDE or PlatformIO. The README in firmware/ walks through setup.)
- 5.Assemble both arms following the step-by-step guide, heat-set brass inserts, wire servos.(Servo calibration is iterative. Start with the base joint and work outward. Expect 1-2h of tuning.)
KNOWN ISSUES
- Cheap MG90S servos have inconsistent dead-band and torque. If you buy unbranded clones, expect 2-3 servos to jitter or stall. Order spares or source from a known-good supplier.
- The non-commercial licence forbids selling assembled units, offering build services, or commercial demonstrations without permission. Hobby use and education are fine; selling one to a friend is not.
- WiFi latency varies by network. If you see lag or jerky motion, check for 2.4GHz interference or move the ESP32 closer to your router. 5ms ping is workable; 50ms is painful.
- Brass inserts must be heat-set squarely or the servo brackets will sit crooked. A crooked bracket adds friction and throws off the mirror mapping. Use a soldering iron tip designed for inserts.
- The follower arm has no load compensation. If you mount a heavy gripper or camera, the servos will lag under load. The 800g payload is for the included gripper only.
- Servo calibration is not documented in fine detail. You will need to write a small test sketch to check center positions and end-stops before the mirror mapping works smoothly.
Can I use different servos?
Yes, but you will need to adjust the servo brackets and recalibrate the firmware. The STEP files are provided so you can modify mounts. Stick to the BOM servos for the first build.
Does it need two ESP32 boards?
No. One ESP32 runs both arms. The leader reads potentiometers (or hall-effect sensors if you upgrade), the follower drives servos. Both arms connect to the same board over I2C or PWM.
Can I control it with a VR headset or joystick instead of the leader arm?
The firmware is structured for a physical leader, but the joint angles are plain floats. You could replace the input source with joystick or VR controller data. Expect a weekend of firmware work.
How much does the print weigh?
Both arms together use roughly 600-700g of PLA at 20% infill. Add ~200g for servo brackets. Total filament cost is about one 1kg spool.
What is the repeat accuracy?
Not documented. Cheap servos have ±1-2° slop. If you need sub-millimetre repeatability, this design will not deliver it without upgrading to closed-loop servos or steppers.
Community builds
No community builds yet — be the first, we feature the best ones.
Discussion1
FROM THE COMPAREE TEAM
28 hours of printing, 16 servos, and you get a follower arm that mirrors your hand in real time. What would you make it grab first?
NormaCore
NormaCore is a Czech hardware collective building open robotics platforms. ElRobot started as an internal teleoperation demo and was released as CC BY-NC-SA in 2024. The URDF and STEP files suggest the team uses ROS for other projects.
Keep building — related projects
Same category, picked by how close they are to this build.
FULL CADDummy-Robot — compact 6-axis desktop robotic arm (15k stars)
RoboticsOpen-hardware●●●●●expert
FULL CADNASA published the plans for its Mars rover so you can build one
RoboticsOpen-hardware●●●●○advanced
Partner · KickstarterCodeeBot: build the robot from Lego-compatible bricks and program it by hand; a GPT tutor explains each step.
FULL CADElectronBot — cute WALL-E-inspired desktop robot (9.4k stars)
RoboticsOpen-hardware●●●●●expert
NO CAD FILESYou can build a palm-sized robot dog that does backflips
RoboticsOpen-hardware●●●○○moderate
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.
CompareeTEAM1mo agoedited
Practical notes from our verification: the repository structure is clean (STEP, STL, firmware, and docs all in expected locations), there is no official video walkthrough, and the single biggest risk is servo variance — cheap MG90S clones can differ by 20% in torque batch-to-batch, which will show up as lag or jitter in the follower. The BOM does not specify a supplier, so budget for one or two spares. The non-commercial licence is clearly stated in the README; this is a hobby/education project, not a kit you can sell.