Ubuntu Summit BrachioGraph is a Raspberry Pi Zero built DIY pencil stylus that comes with low servo motors that cost $2, as well as household parts like clothes pegs, bulldog clips…and controlled in Python.

The fun aspect of the Ubuntu Summit was that unlike some noteworthy events from the business side of the industry, people here were presenting their personal passion projects. BrachioGraph He is one of those, and it was introduced by its creator, Daniel Procidawhose day job is director of engineering at Canonical.

BrachioGraph in action. Pic of Danielle Procida

These days, if you want a hard copy of something big, like an engineering diagram, there are large format printers that will need you, but back in the days, that task fell to XY draftsmen. Decades ago, your author had one, tied to the Archimedes nut. As Procida said, “You don’t really see them anymore, but they were nice to watch in action.”

They were also a very complex group – they have Featured in On CallIn fact More than once. Amateur versions still exist: for example, there is AxiDraw, whose budget is MiniKit About $325.

So, Procida decided to build himself… “But all my tools were to fix bikes.” So, he bought some cheap servo motors for $2 from a Chinese sales site, and used household items for the rest: some popsicle sticks (Ice lollipop), clothespin (clothes clips), binder clip, a sheet of cardboard, and spare parts. Raspberry Pi Zero. “That’s what I had in my hand, and I wanted to do something with it,” It is to explain. “I like to have limits, because when you face a limit, you have a challenge.”

Call it the result Graphfrom ancient greek αχίων (brakhīón) and arm and γράφω (gráphō), to write: “arm clerk.” (This eagle has been a sucker for a classic reference ever since Asterix and Obelix.) Instead of an XY mechanism, the chin chart has a shoulder motor, an elbow motor, and a rudimentary wrist to lift the pen off the paper.

The result is that he can only draw curves: As Procida said, “It is very difficult to do Withdrawal straight line with your arm than to walk one by one.”

To do this, he had to go back to high school trigonometry and Python, with some help from numpy Library. The result is limited: she can only draw on a small, somewhat curved area of ​​u200bu200bthe piece of paper or paper, and her lines are wobbly. Each of the three motors has a limited range of motion of about 120 degrees. He told us, “You can get about 150 degrees, but it gets very imprecise. Any more than that, and they’ll explode. I ruined a lot of those. I’ve never used a single Raspberry Pi—they take so much abuse!—but the servos, the loads” .

He recommends the basic $2 machines: Apparently, more expensive ones actually lead to worse results. (Beware even the cheapest engines: there are engines offered for about $1, but they are fake and don’t work.) A big problem is that the hardware has a non-linear response, and had to allow this in the Python code. You can calibrate your setup by drawing a few preprogrammed lines, measuring the results with a ruler, and entering the resulting values ​​into the code, which improves the output.

The code can do line extraction in bitmap files, and for a more artistic drawing, you can put a charcoal pencil in a clothespin for a drawing-like result.

As you might expect from the person responsible for the Ubuntu documentation, the project and accompanying code are clearly described, especially for a project named version 0.1. It was very fun to watch the machine in action, and Reg The Office of Free and Open Source Software is planning to try to build one.

Youtube video

You can see one in action in the video above. ®


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