CNC Etchasketch Working, need suggestions

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CNC Etchasketch Working, need suggestions

Post by Quint » Wed Jan 09, 2019 3:43 am

Got my hat a couple weeks ago and got it working. My goal is a cordless Etch-a-Sketch inside a clear acrylic case as a demo for the science fair at my kids' elementary school. As you can see in the picture, I've already got it drawing the mascot for the school (a roadrunner). The hat is only using about 300mA so I should be able to get the few hours of run time I need with some 18650s mounted to the back.

My question is, what is the best/simplest way to switch this system on and get it running the program? I don't want to have to plug it into a monitor and keyboard every time it finishes drawing. Ideally the kids could pick it up (with supervision) shake it and press a cycle start button to draw a fresh picture. I'm told it's pretty easy to have any program (like bCNC) start automatically on the RPi at startup. But how do I load the roadrunner program and press start? Is that a python script? I'm not exactly fluent in python but can generally get a program working once someone sets me on the right track. Another option as I understand it is to use an android phone as a display and control it over WiFi. While that would be cool (and something I'd eventually like to try at least once) that's a pretty small screen and would be an extra hassle. Lastly it continues to run even when I unplug everything but power, so if I can get a cycle start button figured out, I could connect a monitor and mouse at the beginning of the science fair to start it then use cycle start each time the program ends. I'd still rather leave it off and just have everything come when I power it on.

Is that pretty much it or am I missing some other option? Any suggestions and pointers would be appreciated. In case you're wondering, I'm compensating for the substantial backlash in the g-code itself with software intended for sloppy 3D printers. Right now I'm using 0.8mm in the X and 1.6mm in the Y. I know I can fine tune it a little more but it's already plenty good for the intended purpose. Thanks in advance for your help.

Etch1.jpg (336.15 KiB) Viewed 124 times

Bertus Kruger
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Re: CNC Etchasketch Working, need suggestions

Post by Bertus Kruger » Wed Jan 09, 2019 6:32 pm

That is an awesome project.

With the RPi it will be a combination of things to get it going. A Cron job can start the drawing script and there is a Python example of streaming g-code on Github >>> ...

Getting the script to run on the startup might be the easiest and then just restart the RPi. (I would take a few backup SD cards incase the restart corrupts the image)

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