YOU CAN BUILD A DRAWING ROBOT OUT OF TWO STICKS AND A PENCIL FOR ABOUT 14 EUROS
A drawing robot made from two sticks, three cheap servos, and a Raspberry Pi Zero that plots sketchy line art for about fourteen euros.
RoboticsDisplays
Built withRaspberry Pi
- difficulty
- ●●○○○
- time
- an evening
- license
- MIT
- repo
- repo ACTIVE750 stars
●●○○○ · an evening · MIT · 750 stars · repo ACTIVE
WHAT YOU’LL NEED
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COMPAREE VERDICT
BrachioGraph is a pen plotter designed to be built in about an hour from parts you can find in a drawer or buy for under twenty euros. The mechanics are deliberately minimal: two wooden sticks or lolly sticks for the arms, three SG90 hobby servos, a pen, and some glue. A Raspberry Pi Zero runs the Python software that converts a photo into a line drawing and then sends servo commands to plot it. The draw is not precision — the cheap servos and the rigid stick geometry mean the lines come out loose and sketchy, which is exactly the aesthetic the project leans into. The documentation is thorough and honest: it walks you through assembly, wiring, calibration, and troubleshooting, and it explicitly says the calibration step is fiddly because the servos are inconsistent. The most likely failure is skipping calibration and wondering why the output is worse than the examples — the servos need individual tuning. This is not a plotter for technical drawings; it is a plotter for portrait sketches and wobbly art that looks hand-drawn because it almost is. If you want a weekend project that produces something genuinely charming and costs less than a movie ticket, this is it. If you need repeatable accuracy, you are looking at the wrong machine.
IN THE REPO
GOOD TO KNOW
- —Complete Python software and detailed documentation in the repository.
- —Bill of materials is embedded in the tutorial pages, not a separate file.
- —No CAD files because the mechanical structure is two sticks and glue — dimensions are specified in the docs.
- —MIT licence permits commercial use.
- —The project's own estimate is about €14–15 for the whole machine, Raspberry Pi Zero included; genuine SG90 servos and a separate power supply can push it higher.
- —Calibration is manual and essential — the repository includes a whole page on it because the cheap servos drift.
Parts to buy
7 itemsFrom our check of the build. Exact quantities and part numbers are in the creator’s BOM.
Can I build this?
Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.
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Start here
Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.
- 1.Read the 'Get started' page in the documentation to understand the build and what you need.(This page lists the parts and walks through assembly with photos.)
- 2.Order three SG90 servos and prepare two sticks — lolly sticks or wooden coffee stirrers work.(Sticks about 10 cm long work. What matters is the geometry: the tutorial puts the centres of rotation exactly 8 cm apart on both arms, which gives a drawing area of about 14 x 9 cm, enough for A5 paper.)
- 3.Set up the Raspberry Pi with Raspberry Pi OS and install the BrachioGraph Python library.(Install a few system packages (including the pigpio daemon), create a Python virtual environment, clone the repository and run pip install -r requirements.txt. The tutorial gives the exact commands for Raspberry Pi OS and Ubuntu.)
- 4.Assemble the plotter following the build instructions, then work through the calibration page.(Calibration is manual and essential — the servos are cheap and inconsistent.)
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 ~€14 estimate is tight. Genuine SG90 servos cost more than the cheap fakes the docs warn about, and a separate power supply for the Pi makes it more reliable, so budget a bit more if you are starting from scratch.
- Skipping calibration is the single biggest mistake — the servos drift and the geometry is never perfect, so you have to tune each servo's range or the drawings will be worse than the examples.
- Counterfeit SG90 servos are common. The docs say servos sold as SG90 for under 3 euros each are probably fake and recommend a reputable retailer. Stick to analog servos: small digital ones such as the SG92R oscillate wildly in this mechanism.
- The sticks must be rigid — flexible sticks or uneven glue joints will make the pen wander even more than the servos already cause.
- The plotting software is Python and runs on the Pi itself, so you need SSH or a monitor to interact with it — there is no standalone app or web interface.
- The sketchy line quality is inherent to the design — if you want plotter-grade precision, you need a different machine with stepper motors and linear rails.
Can I use a different Raspberry Pi model?
Yes — the software runs on any Pi, but the Zero is recommended because it is cheap and low-power. A Pi 4 will work but is overkill.
Do I need a specific brand of servo?
No specific brand, but you need fixed-range analog servos with about 180 degrees of rotation. SG90s are recommended; the docs report good results with Miuzei SG90 and the larger Futaba S3001. Avoid small digital servos such as the SG92R, which oscillate in this mechanism, and continuous-rotation servos.
Can I plot on something other than paper?
Yes, as long as the surface is flat and the pen can write on it — card, wood, and fabric all work if the pen is right.
How do I improve the line quality?
Better servos and stiffer arms will help, but the sketchy quality is part of the design — if you want clean lines, you need a different plotter architecture.
Is there a way to plot without a Pi?
Not with this software — the BrachioGraph library is Python and expects to run on a Pi. You could port the code to Arduino, but that is a different project.
Community builds
No community builds yet — be the first, we feature the best ones.
Discussion1
FROM THE COMPAREE TEAM
The project says the whole build takes about an hour and costs around fourteen euros, Raspberry Pi Zero included. What would you plot first if you built one this weekend?
Daniele Procida
Daniele Procida, known for his work on documentation (the docs follow his Diátaxis structure), created BrachioGraph in 2019 as the world's cheapest, simplest possible pen plotter, with Python software and a step-by-step tutorial.
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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 has not moved, and the full documentation lives on brachiograph.art (the old readthedocs address redirects there). The documentation is unusually thorough for a hardware project: a step-by-step tutorial from construction and wiring to first plots, followed by chapters on improving the output, more sophisticated calibration and working with the hardware's limitations. The project site also has a short video of a BrachioGraph drawing, and the construction page embeds a community build video. The cost figure is genuinely low: the documentation puts the whole build at about 15 euros including the Raspberry Pi, hobby servos and household items, and the README says about 14 euros. The thing to plan time for is calibration: the cheap servos are imprecise, and the docs warn that SG90s sold for under 3 euros are probably counterfeit. 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.