Close
0%
0%

Arrakis Sand Table

A table that draws patterns in sand.

Similar projects worth following
I'd call this a 2nd generation table, but the first one, The Spice Must Flow, went through about 5 major design changes, so maybe this is better called 6th generation. The table uses a redesigned and 3D-printed corexy mechanism with sliding PTFE bearings to move a neodymium magnet that pulls a steel ball through a thin layer of sand, leaving behind interesting patterns. The patterns are lit from low angles by red and blue LED strips, lighting ridges red on one side and blue on the other, with dark shadows in the valleys between ridges.

This is a project that's got a lot of off-the-shelf electronics and open source software to control the mechanism. Unlike most other sand tables you may have seen around the web, this one is powered by servomotors that allow insane speed and acceleration, operating at very low to low noise level, even at high speeds.

I'll be posting a lot of details to my blog, and post a link to it soon. In the meantime, here is some basic information about the table.

General

I put a lot of effort into making the mechanism and electronics reliable and quiet., and largely succeeded. It is also capable of extraordinary speed and acceleration (for a sand table, anyway).  My sand table running in real time looks like other sand table time-lapse videos.  I routinely draw patterns at 500-1000 mm/sec but the table is capable of almost 2000 mm/sec.  Acceleration can go up to 2gs before it throws the ball, though I normally run it at 5k-10k mm/sec^2.

The Mechanism

Arrakis uses a belt driven corexy mechanism powered by servomotors with 20 tooth pulleys. The frame is made of 45 mm square t-slot aluminum and all the mechanical parts fit inside the rectangular frame. The slots in the long rails serve as guides for the Y axis with sliding PTFE bearings. The X axis guide is a square aluminum tube and it too, uses sliding PTFE bearings to keep noise down. Pulleys are made from stacked F625 bearings. All bearing, pulley, motor mounts, and the magnet carriage are 3D printed. The table uses a 1" cube, N52 neodymium magnet. Patterns are drawn using an 11mm steel ball. 

Electronics

Each motor has its own power supply, as does the Duet 2 WiFi controller board. There are two LED strips, red and blue, that are each powered by buck converters connected to one of the motor power supplies.  The motors are iHSV 78W (there's no kill like overkill!) Nema-17 integrated servomotors. They are driven by step/direction/enable signals from an expansion board plugged into the Duet controller. The Controller has a web server that can be accessed to control the table via phone or laptop computer.

The Sandbox

is made with 1/2" walls and a 1/4" bottom from Baltic birch plywood. There's a layer EPDM rubber on the bottom of the box to minimize noise from the ball rolling. The sides of the box are finished with 1/2" high density upholstery foam covered with red and blue striped fur cloth.  The box is mounted so that there's an air gap between the bottom of the box and the magnet to minimize noise. The top cover consists of an oak frame that has been stained and finished with oil based polyurethane which holds a tempered glass cover. The cover was put at coffee table height and the bottom of the sandbox placed close to the floor to keep sand from sticking to the glass. The sides of the box come down almost to the floor to keep Ms. Kitty from getting under it and chewing on wires or belts.

Software

Patterns are generated using Sandify. I wrote a post processor to take advantage of the high speeds that the servomotors can provide. The post-processor allows two speeds to be set in the pattern files- a low speed for drawing the pattern and preserving detail, and a high speed for travel around the edges of the table. Now, for example, I can specify that  the drawing should occur at 100 mm/sec and the edge motion at  1000 mm/sec. In some patterns with a lot of edge motion the result is a significant reduction in pattern completion time and reduced boredom if you're watching the table draw the pattern.

View all 2 project logs

Enjoy this project?

Share

Discussions

Ossum wrote 09/20/2021 at 08:09 point

Beautiful pictures, the two colours really look great. Do you have a video of it in action?

  Are you sure? yes | no

Mark Rehorst wrote 09/20/2021 at 19:12 point

I'll shoot some video in the dark tonight and post it. In the meantime, there's this video demonstrating the dual speed post processing: https://www.youtube.com/watch?v=Z_B7TTNTJzc

  Are you sure? yes | no

Mark Rehorst wrote 09/21/2021 at 04:38 point

Here's a video shot in a dark room. The table is drawing at 200 mm/sec. It can go much faster- I'll post a high speed video tomorrow.

https://youtu.be/NoC4QaVx97M

  Are you sure? yes | no

Ossum wrote 09/21/2021 at 08:53 point

Really really awesome, great work, thanks for sharing! It is incredible how quiet you managed to make it.

  Are you sure? yes | no

Similar Projects

Does this project spark your interest?

Become a member to follow this project and never miss any updates