It really isn’t but I was inspired by your builds and I first came across sand tables here when researching my Lowrider 2 so I thought I’d share it here.
I am a fan of round tables but I always felt the polar construction was pretty weird. I have a SCARA design in mind. Also, I wanted it to be low cost and achievable with what most of us here have: A CNC router.
And this is the concept for the gearbox and the arms. I have ordered parts to move the belt under the upper arm, allowing me to slide the upper and lower arm directly one over the other. I hope that will be stiff enough to avoid the lower arm being bent up by the magnet so that I get no scraping on the underside.
Still ways to go, especially with the software, but it’s been fun so far…
Looks cool, and very interesting. Maybe I just don’t understand, but the SCARA design seems like it uses “nested” polar construction anyway, no? Looking forward to more.
You’re absolutely right, if you go round it has to be some kind of polar, I guess. I meant the “on the nose”-way of the theta rho design of the Sisyphus.
I want to be able to feed my machine GCode so I have to do conversion and segmenting anyways. I thought I might as well go all in and do that for the arm-on-an-arm design I’ve always wanted to do…
Impressive work!
I´m also a huge fan of polar table style building. They simply look really smooth and I like the possibility to build a round table. When I had my first go at building a sandtable I was trying to do a spin off designing an own version of the famous Sisyphus pinion construction but never managed to finish it.
During my research I found this clever guy which has a nice design available. He also has some Scara calculations and examples.
My naming convention is: “Upper arm” is the one connecting shoulder and elbow, like on our bodies, even though when you look at it from the side it is the one positioned below the other.
For my software development these will have to do but eventually I’m planning to move the belt underneath the upper arm. Then I can have a larger “elbow” area (disk shaped) where the two arms sit flush to avoid any play in the Z axis. That would be hard to achieve otherwise, with only 6mm strength in the arm material. For the moment, I have doubled that up by using two layers of material for the upper arm.
This is my plan for a table, should this prototype prove capable of moving a ball around:
Yes, I have, thank you very much! I’m taking inspiration from it but since I don’t own a 3D printer nor a laser cutter I have to make my own design anyways. Plus, I didn’t want to use NEMA steppers because I find their whining a bad fit for a meditation piece like this.
The gears in my prototype rattle quite a bit, too, but I have hope that once I close the case, decouple it with rubber and maybe put some insulation around it that will be less of an annoyance than “real” steppers. (Maybe other drivers would solve that?) Also: The 28BYJ-48’s were dirt cheap.
I’m not so sure about the programming side as I seem to remember he used a pre-processor and I wanted to be able to do it on-machine but it certainly is close enough for me to be able to use portions of it…
