I spent part of Saturday working on my latest plotter project.

We spend a lot of our time making art with pen plotters, and I’ve become really interested in all aspects of the machines – from the varied combinations of inks, pens, and papers that can be used to create unique and individual designs, to the software and hardware of the devices themselves.

The primary two plotters that we use in the studio are an AxiDraw, and a Roland DYX-1100. I’ve also built a BrachioGraph, and a hanging Polargraph. My current project is a CoreXY plotter.

This is a series of modifications on top of a basic plotter kit that I picked up on AliExpress. By default, the plotter comes with a clone Arduino UNO board, and a motor shield. It’s a cheap(ish) kit, that came with some largely pictorial assembly instructions, and far too many parts. You can read a write-up of a similar machine over here.

The majority of these kinds of devices run GRBL, an Arduino firmware that works with Gcode – I already did a lot of hacking with that as part of the Pico-based polagraph project, and I was also looking for a way to improve the speed and configurability as well as adding wireless connectivity. So, instead of sticking with the vanilla build, I decided I was going to upgrade the machine to FluidNC, which is a newer firmware based on ESP32.

I’ve replaced the Arduino attached to one side of the X axis, with a FluidNC board with 2 TMC2209 motor controllers. On top of that, I added some copper heatsinks on the motor drivers. I still need to design and print a new box holder for the controller, to replace the one I removed from the plotter – I don’t actually want that to be floating around on a nest of wires off the side of the machine.

In addition, I’ve added limit switches on the negative (min) sides of the X and Y axes; wired them via the existing cable holes; and, replaced the original coiled plastic cable covers with better quality cable sleeves. I’m pleased with these improvements. There’s technically the option to add another pair of limit switches on the max sides of the axes, but I wasn’t intending to add them as well.

So far, so good; well, I’m happy with things on the hardware side, at least. I made the modifications one by one, and I can see the limit switches tripping when the axes run through the homing process.

The largest issue I’m having is the calibration. I haven’t changed the motors or the dimensions of the machine, but, I’m also not confident that the GRBL build on the Arduino was accurate in the first place (the plotter came with a zip of various bits of code, but I’m not sure that it reflects the specifics of the plotter), so I’m not completely sure that the parameters directly transfer to the FluidNC configuration. This is not straightforward for me – although I’m a coder, I’m not always great at the mathematical side of things, and between spindles, rotations, steps, and power ratios, I’m having “fun”. Although I’ve got most of a working FluidNC config, there’s clearly something off in the settings, as I’m still (!) seeing the machine try to shoot past the limits, and then I have to pull the power.

Once I’ve got this working, I’ve also got a couple more DIY-build plotter projects in mind… if only I have the room for them all…

andypiper.co.uk/2024/07/20/hac…

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