Polar robot arm for sand table, many glow forge cut parts

The forge is great for rapid prototyping. I am building a zen garden sand table and the guts are mostly bits of plywood from the forge ( base, mounts, spacers) Being able to change the mounting points in a matter of minutes allowed this come together with minimal heartache. I got all the electro-mechanical bits working and wanted to share. Video and more photos here The 27 second long video shows the currant state of the bot.

So, a central pivot with a linear slide mounted on top. a pair of stepper motors and a limit switch. All controlled by an arduino with a CNC shield . A magnet will be mounted to the slide and then entire thing will be positioned just under a bed of sand. The magnet will drag a steel ball through the sand to create patterns.


Sounds really cool (although a robotic Zen garden strikes me funny). Please, I would love to see the finished project. I bet it will be fascinating to watch.


I have everything ready for an MPCNC build from V1engineering. Just haven’t had time to dedicate to assembly. One more unfinished project on the list.

His Zen table is pretty cool.

Here is SomeOldGuyCoding’s build:


One of these have been on my list too.

that seems to be an x-y plotter base but a similar idea. by virtue of his being x=y, he can get into corners while mine will be constrained to an outer diameter. I am scaling this to fit into an existing table so the diameter will be abut 31 inches or so.

this is my inspiration for this.


That should have been the title…and the first sentence… still got me anyway… ha😎

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The Sisyphus is beautiful!

I would really love to do one of these. I had impossible internet speeds yesterday so couldn’t get this link from the original designer copied to post.



I was skeptical at first and now I want to build one.


that tensioner looks wonky to me. you are going to beat the living crap out of that belt.

I just had a chance to look at the video. in the picture above it looks like that spring is mounted on the arm. and you were going be pulling the belt through the spring. Whew!!! it moved. :slight_smile:

It never passes through a pulley. What is the issue?

The community just keeps topping yesterday

See my reply above. the picture looked like the spring was mounted and the belt was going to be grinding through it…

some progress

a video of it in action is here

still working some of the kinks out on some patterns but this gives the flavor


Very nice. I’ve been wanting to do one of these for a long time. Too many projects. :slight_smile:

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This is so far out of my ability and knowledge I am embarrassed. However, I feel so fortunate to be part of this forum to be able to see and learn about things I never even dreamed about. Thanks for sharing with us mere mortals.

10 years ago, I could not do any of this. Never say never.

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Trust me, I will keep trying and learning. I ‘retired’ from my career about 12 years ago and I swear my brain cells died off quickly as I have been largely taking care of and homeschooling my youngest. Now that she is becoming much more self-sufficient I am able to once again dive into learning things just for me. I have tried to keep up to date in computers, Photoshop, etc so I was able to quickly teach myself Illustrator over the last couple of months. Next, I WILL figure out Fusion if it takes every last one of my brain cells. I’d prefer not to wither in a corner when she launches in just a few years LOL


One is reminded of the story of the first-grade teacher that managed to hit a pole with her new car on the way out of the sales lot getting out and looking and saying “Oh, Oh, Oh… Look, look, look,…Damn, damn, damn” :slightly_smiling_face: