BrachioGraph – a cheap, simple pen plotter • Hacker News Board

Re: BrachioGraph – a cheap, simple pen plotter

#51

Post by ISL » Thu, Oct 17, 2019, 3:24 PM UTC

xVedun wrote: post #37

ISL wrote: post #32

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

Pi Zero ($5): https://www.adafruit.com/product/2885 4 Servos ($9): https://www.amazon.com/dp/B07Q6JGWNV/ref=cm_sw_em_r_mt_dp_U_... Shipping might go over $14 though.

So cool. Thanks!

Re: BrachioGraph – a cheap, simple pen plotter

#52

Post by dougmany » Thu, Oct 17, 2019, 3:27 PM UTC

Ididntdothis wrote: post #12

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.

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.

Re: BrachioGraph – a cheap, simple pen plotter

#53

Post by philpem » Thu, Oct 17, 2019, 3:28 PM UTC

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.

Re: BrachioGraph – a cheap, simple pen plotter

#54

Post by th0ma5 » Thu, Oct 17, 2019, 3:29 PM UTC

hrnnnnnn wrote: post #23

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?

I bought a kit called the EleksDraw and found it for $140 shipped. It uses G Code and didn't take too long to put together maybe a couple of hours at a slow place.

Re: BrachioGraph – a cheap, simple pen plotter

#55

Post by MisterTea » Thu, Oct 17, 2019, 3:58 PM UTC

iamgopal wrote: post #41

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

You could get a lot more precise with stepper motors paired with a micro stepping drive. Since a stepper does not necessarily need feedback the software doesn't have to close a loop but spit out position and velocity commands. Integrated stepper chips exist on breakout boards which keeps the design simple as it will handle the complex microstepping current control. The entire design would not increase much in complexity at all and gain a massive amount of precision.

Re: BrachioGraph – a cheap, simple pen plotter

#56

Post by C1sc0cat » Thu, Oct 17, 2019, 4:14 PM UTC

hrnnnnnn wrote: post #23

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?

A more rigid frame and an X Y layout of the servos maybe an maybe a port of GINO-F

Re: BrachioGraph – a cheap, simple pen plotter

#57

Post by C1sc0cat » Thu, Oct 17, 2019, 4:17 PM UTC

Ididntdothis wrote: post #12

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.

Back in the day we used to use HP's biggest and badest Super A0 plotter for small print runs used to park it the computer room (to keep the temperature controlled) and let it run all nig

Re: BrachioGraph – a cheap, simple pen plotter

#58

Post by carapace » Thu, Oct 17, 2019, 4:22 PM UTC

hrnnnnnn wrote: post #23

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?

I'd say the next step up would be something like the Morgan RepRap: https://reprap.org/wiki/RepRap_Morgan

Re: BrachioGraph – a cheap, simple pen plotter

#59

Post by carapace » Thu, Oct 17, 2019, 4:24 PM UTC

ISL wrote: post #51

xVedun wrote: post #37

Earlier quoted context omitted.

Pi Zero ($5): https://www.adafruit.com/product/2885 4 Servos ($9): https://www.amazon.com/dp/B07Q6JGWNV/ref=cm_sw_em_r_mt_dp_U_... Shipping might go over $14 though.

So cool. Thanks!

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

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

Re: BrachioGraph – a cheap, simple pen plotter

#60

Post by carapace » Thu, Oct 17, 2019, 4:32 PM UTC

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".