
BrachioGraph – a cheap, simple pen plotter - DanieleProcida
https://brachiograph.readthedocs.io/en/latest/
======
gknoy
This documentation is very impressive. I like that the author included a link
to "Why is the documentation structured this way?" [0].

0:
[https://www.divio.com/blog/documentation](https://www.divio.com/blog/documentation)

~~~
aurbano
That’s extremely well written!

I’ve been struggling to document an open source platform I’ve built with some
friends and colleagues [1] and this is finally giving me hope!

[1] [https://play.socialgorithm.org](https://play.socialgorithm.org)

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lukey_q
Awesome to see pen plotter stuff posted here with more frequency. This project
is pretty amazing in its frugality, kudos to the author. I have another pen
plotter and I'd highly recommend pen plotting to anyone who's into generative
art or anything similar, it's really fun to write a few lines of code to
generate some visuals and then watch the plotter as your design is made into
something tangible.

I'm working on a (free) app around making drawings on your computer, putting
some effects on them, and sending them directly to a pen plotter. So far it
only works with axidraw because that's the only one I have, but ultimately
it's just sets of coordinates so it could be adapted for other plotters pretty
easily. I'll post it here once it's in a decent state :)

~~~
romwell
FWIW, every 3D printer is also a pen plotter (just stick a pen to your print
head!).

Here's my old faithful Printrbot plotting a dragon curve:

Fountain pen, timelapse:
[https://www.instagram.com/p/BlQHk43gwra/](https://www.instagram.com/p/BlQHk43gwra/)

Fountain pen, final image:
[https://www.instagram.com/p/BlJHawZgFi1/](https://www.instagram.com/p/BlJHawZgFi1/)

Ballpoint, realtime:
[https://www.instagram.com/p/BlJ8dgmAaTA/](https://www.instagram.com/p/BlJ8dgmAaTA/)

~~~
aallen90
That's awesome! What print speed did you use? (your steppers sounded like it
was very high) And do you slice 1st layer normally?

~~~
romwell
Thanks! I didn't use a slicer, went straight into G-code for that one (wrote a
program that generates the G-code for the dragon curve: a sequence of G0
commands).

Don't remember what the feedrate was; with the pen attached tight, I could go
pretty fast.

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frankwiles
Daniele had it do my portrait at DjangoCon last month and it turned out pretty
well despite the fact I'm so hairy!
[https://twitter.com/fwiles/status/1177018222987448321](https://twitter.com/fwiles/status/1177018222987448321)

~~~
test1235
did you have a belt across your face?

~~~
frankwiles
hahaha no

~~~
Cheyana
It looks like the robot adds 10 pounds.

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hrnnnnnn
This looks like great fun, but I'd prefer to make something where the output
is a little more precise.

Does anyone know of a DIY plotter that's a step up quality wise from this one?
Or maybe a site or community that lists similar projects?

~~~
sleepybrett
I love my evilmadscientist axidraw but honestly they are a bit pricey. There
are several chinese knockoff kits to be found on alliexpress/banggood/etc that
work very well. There are also a few interesting 3d printed projects to be
found on thingiverse and in the greater maker community. I've built a midtbot,
fun little project if bart has boards available
([https://www.thingiverse.com/thing:2587684](https://www.thingiverse.com/thing:2587684))
and I've got the full BOM and have printed most of the parts for a modest
sized d.i.d. plotter
([https://www.thingiverse.com/thing:3789969](https://www.thingiverse.com/thing:3789969)).

Also don't discount polar style hanging plotters they can be tricky accuracy
wise due to sway, which i've seen countered both by decreasing plotting speed
and by working the potential sway into your design. Just a quick search turned
up this [https://www.hackster.io/fredrikstridsman/stringent-
the-15-wa...](https://www.hackster.io/fredrikstridsman/stringent-the-15-wall-
plotter-d965ca). You can start small like that and then improve components
along the way. Swapping the string for beaded cord or timing belt etc. They
are patricularly interesting drawbots because if you want to plot a larger
area you can just spread out the motors and add more string.

~~~
panpanna
Fredriks design looks really interesting!

Vertical plotters are usually hard to install and calibrate but his looks like
one you could slap on coworkers whiteboard and print something while he is on
lunch break ;)

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cpach
If you’re in to this kind of stuff, you might want to check out the hashtag
#plotterwitter. Some really good stuff there.

[https://twitter.com/hashtag/plottertwitter](https://twitter.com/hashtag/plottertwitter)

~~~
RickS
Nice! I've been enjoying the work from skullcat recently:
[https://twitter.com/mrmrs_/status/1159339640459059200](https://twitter.com/mrmrs_/status/1159339640459059200)

------
DanieleProcida
Some more images of and by the plotter:
[https://www.dropbox.com/s/fuifujd70jvn7lw/brachiograph-
image...](https://www.dropbox.com/s/fuifujd70jvn7lw/brachiograph-
images.pdf?dl=0)

~~~
nmstoker
Produces a wonderful artistic effect! Great project Daniele!

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Ididntdothis
I love pen plotters. When I worked with CAD we still had them. It was so much
fun seeing it slowly working on a technical drawing. Laser printers are
obviously much better and faster but much less fun to watch.

~~~
dougmany
Oh yeah. When it would change colors it would run over to the pen holder and
pick up a new color. That was fun to watch.

~~~
ficklepickle
That reminds me of the create-a-card machine that was in Hallmark stores in
the 90's!

I had forgotten about that. I remember watching in awe as it drew a Simpsons-
themed card.

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HeWhoLurksLate
This is awesome! To the people that made this happen: Thank you so much!

I've been wanting something to demonstrate how the gap between hardware and
software is fairly easy to bridge at this point- thank you for sharing
something that demonstrates this well!

------
DanieleProcida
On GitHub:
[https://github.com/evildmp/BrachioGraph](https://github.com/evildmp/BrachioGraph)

------
DanieleProcida
Thanks for all the interest and kind remarks this has received. I have updated
the documentation substantially and included more photos in it.

------
timthorn
And if you want a COTS replica with a bit more polish: [https://www.line-
us.com/](https://www.line-us.com/)

~~~
itronitron
The line-us looks really good, the software also looks well put together.

~~~
person_of_color
Is it hackable?

~~~
itronitron
It looks like people can code Scratch to control it...

[https://www.line-us.com/scratch.html](https://www.line-us.com/scratch.html)

... and there is also a programming tab that links to a github page with lots
of example code in other languages.

------
ISL
Where can we buy a Pi and three servos for $14? That sounds darn fun.

~~~
xVedun
Pi Zero ($5):
[https://www.adafruit.com/product/2885](https://www.adafruit.com/product/2885)
4 Servos ($9):
[https://www.amazon.com/dp/B07Q6JGWNV/ref=cm_sw_em_r_mt_dp_U_...](https://www.amazon.com/dp/B07Q6JGWNV/ref=cm_sw_em_r_mt_dp_U_nbiQDbCF84TB2)

Shipping might go over $14 though.

~~~
ISL
So cool. Thanks!

~~~
carapace
Don't buy servos from Amazon though: you could get anything.

Spend a few more bucks at e.g. Digikey, eh?

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diafygi
It's my understanding that higher quality plotters/3d printers/mills' accuracy
and precision come from higher quality motors (e.g. stepper motors instead of
servos). Will it be possible to someday just put cameras on the plotter which
watch the current print and self-correct as needed? That's basically what our
eyes do when we write/sculpt/carve.

Will cheap motors + cameras + software eventually meet or exceed the quality
of expensive high precision motors/controllers?

~~~
yakz
Rigidity is a major factor--if you inspect one you'll notice that high speed
and high repeatability machines (e.g. a 6-axis +/\- 0.020mm repeatability
manipulator) are made from rigid (often high-mass) components with robust
joints.

~~~
diafygi
I see. I wonder if my hypothesis is still valid, even given lower quality
rigidity. Human arms aren't made of big heavy metal rods, yet we can still
draw beautifully. Couldn't cameras and software compensate for cheap unstable
draw arms?

------
philpem
I remember a similar Mike Cook "Beeb Body-Building" article from Micro User.
He used a similar layout and two potentiometers to build a "radius-arm
digitiser".

A little bit of calibration and some trigonometry and you can work backwards
from the pot positions to Cartesian X/Y co-ordinates.

A little bit more work and you can enter line points from a paper drawing into
the rudimentary CAD systems which existed on the BBC Micro at that time.

------
joquarky
Someone at my local makerspace made something like this, but for vertical
surfaces.

[https://github.com/brandonagr/gocupi](https://github.com/brandonagr/gocupi)

~~~
jstanley
It's a shame the repository doesn't have any examples of the pictures it's
drawn.

There are some on
[http://brandonagr.github.io/gocupi/](http://brandonagr.github.io/gocupi/)

------
makotoNagano
Nice stuff. Raspberry Pis are generally pretty terrible at running servo's
though. Adding an intermediate Arduino would work wonders (I appreciate the
complexity would jump significantly though)

~~~
DanieleProcida
Turns, out, it's actually very reliable in practice. I'm trying to work out at
the moment just how far I can go with more powerful servos:
[https://raspberrypi.stackexchange.com/a/104662/42583](https://raspberrypi.stackexchange.com/a/104662/42583).
There are limits, but they seem to be greater than I expected, especially when
the only power to the Raspberry Pi is provided by a MacBook.

~~~
dekhn
we live in a world where a macbook can power a raspberry pi which powers
servos.

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carapace
Ooo! Combine this with a sand table, the arm draws in the sand w/ a stylus,
and add a little vibration motor to "erase" the "screen".

------
akamor
Is there a video somewhere of this in action?

~~~
cbertschy
[https://youtu.be/Rn4X2ZgZvsk](https://youtu.be/Rn4X2ZgZvsk) and
[https://youtu.be/u4Jh1daCl60](https://youtu.be/u4Jh1daCl60)

------
antcas
Reminds me of [https://www.handwrite.io](https://www.handwrite.io)

~~~
Frodo478
Wow, that's reminds me of Her (Spike Jonze)

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Autowired
This is amazing and I want to add something like this to my side project list
right now.

But maybe it is a bit too extreme, i.e. using a ruler and glue won't save you
that much money compared to using some better materials. But I guess that was
the intention of the author, extreme frugality.

------
ashish01
I am a complete n00b at this but very interested in making a CoreXY plotter. I
get struct at how to get parts like linear guides and servos needed for this.
What is the best way to educate oneself about this. Is there something like
sparkfun how mechanical hardware. Thanks!

~~~
all2
My goto while building a 3D printer is this:

[https://hackaday.com/2018/08/03/classy-corexy-build-
breaks-d...](https://hackaday.com/2018/08/03/classy-corexy-build-breaks-down-
the-design-pinchpoints/)

------
bullen
If you like this and have some dough:
[https://axidraw.com](https://axidraw.com)

If you have less, google 4xidraw...

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edge17
I like the layout of this site, what is being used to present the
documentation on this site? Or is it a fully custom built site?

~~~
swsieber
I think it's the standard [https://readthedocs.org/](https://readthedocs.org/)
standard. It's definitely not custom. I've seen many projects with it.

Edit: Seems to be linked to the doc tool called Sphinx.

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allenu
Really cool hardware, but I wish there were a bunch of more photos of plots on
the page! I want to see the output.

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aleksgrach
I have never seen such a device, now I will tell the artists.

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iamgopal
What is the best way to increase accuracy of such servo motor ?

~~~
pp19dd
Better motor control.

Timing: assuming rigidity of linear position is crappy, allow more time for it
to bounce back.

Speed: ramp-up speed in one direction may be different from the opposite
direction.

Position: accuracy of RC servos is almost not worth measuring, so many
companies haven't. But you can hack it (via contact switch and something that
juts out) to add a simple shaft rotation encoding and correct when needed.

Software correction: draw a grid of straight lines and adjust drift in
software until it looks like a grid.

~~~
DanieleProcida
Also it's hard to defeat hysteresis in the system, both in the servo motors
(they have significant dead bands) and the mechanical arrangement of the
arm/pen.

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FinalAngel
Had the chance to see it live once in Amsterdam _thumbsup_

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cbertschy
I saw it in action, draws beautiful and unique pictures :-)

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kareninoverseas
This is great! Thanks for sharing.

