Close
0%
0%

The Spice Must Flow Sand Table

A sand table project for the Milwaukee MakerFaire

Similar projects worth following
A 1.9x1 m table with a hidden corexy mechanism and a layer of "sand" through which the mechanism pulls a steel ball to create geometric patterns.

This started out as a cable driven mechanism, but I converted it to belt drive when I found cables to be a bit too troublesome.  It's a single level corexy mechanism with 3D printed motor mounts, pulley blocks, and Y axis bearing blocks.  The Y axis uses UHMW PE blocks riding in slots in the 45 mm square t-slot frame for guidance.  The X axis guide is a piece of 16 mm square aluminum tubing.  There's a 1" cube neodymium magnet that sits in a 3D printed carriage.

I used stacked F623 bearings for pulleys, but found there were some problems with the flanges being too small and the belt tends to climb and ride on them, so I'll be converting to some pulleys with much larger flanges.

Sand table printed parts
The printed parts of the mechanism are yellow. No fancy linear bearings or guide rails used- just the slots in the frame for the Y axis and a piece of square aluminum tubing for the X axis.  Belts are tightened by moving the motor mounts in the slots then tightening the bolts.

The top cover and base frame are made from 45 mm square aluminum t-slot picked up from a local scrap yard.  They are identical size, and the wood part of the table is designed slightly larger so that the top cover drops into the wood frame and the wood part drops onto the base frame.  I painted the wood parts flat black as this will be operating in a dimly lit room at the Milwaukee MakerFaire.  The "sand" will be about 50 lbs of sodium bicarbonate blasting media.  It's pure white and will provide great contrast with the flat black table.  It will be lit with red and blue LEDs.

The mechanism uses two NEMA-23 motors I had handy (NEMA-17 would easily provide the needed torque) with 40 tooth drive pulleys and 6 mm wide GT2 belt.  I copied the belt clamp on the magnet carriage from my 3D printer's Z axis- just a slot with a short piece of GT2 belt to engage the teeth.

magnet carriage for the sand table
This is the magnet carriage. The 1" cube magnet sits in the suqare hole, on top of a spring that sits in the round hole. The spring keeps the magnet pushed against the bottom of the table top.

I'm driving the mechanism with a smoothieboard controller I recently took out of my 3D printer when I installed a Duet board.  An SD card will be loaded with patterns to print that will just run continuously and overwrite each other.

Current status is 90% complete.  I added a corrugated cardboard cover to the bottom of the mechanism to keep people's hands out of it.  Testing with media to begin in a day or two.

  • A new magnet carriage

    Mark Rehorst11/09/2018 at 19:40 0 comments

    I emptied the sand and took the table home from the makerspace to work on it and when it was time to test it, I decided to see how my cat would like it.

    World's Greatest Cat Toy? from Mark Rehorst on Vimeo.

  • A new magnet carriage design

    Mark Rehorst11/04/2018 at 13:14 0 comments

    After the MakerFaire I opened up the table to check on the mechanism and found the magnet carriage badly worn.  The carriage was made of printed ABS and it was sliding on a powder coated aluminum X axis guide tube.  ABS/powder coating is not a good combo, and the ABS loses.

    Old magnet carriage design.
    Old magnet carriage worn bearing surface and cracked body.

    I have redesigned it to use a 1" square aluminum tube that fits over the 16 mm square X axis guide tube with room for UHMW bearings.  Milled slots in the carriage tube anchor the belts and hold the bearings in place. 

    In this design, the aluminum takes all the belt tension force, so there's none applied to printed parts.  The magnet box is held on with zip ties and can be changed easily to experiment with different magnets.  It may need some indexing to prevent it from twisting.  The fit is a little tight right now, but I intend to sand blast the powder coating off the X axis guide tube and I think that will loosen it up a bit.  If I have to I can sand the bearings down a little to loosen the fit.

    More details here...

    New magnet carriage design for the sand table. from Mark Rehorst on Vimeo.

  • It worked.

    Mark Rehorst10/04/2018 at 14:02 0 comments

    The sand table made its public debut at the Milwaukee MakerFaire last weekend and worked well.  It was very popular and I got a lot of nice comments about it.

    There were a few problems...

    The power cord got kicked out of the wall twice (how do you design against that?)

    I started off using ball switching which would work for the first few changes, but would jam up with sand and then stop working, so I removed the ball changer and let the thing run with just 1 ball.  I will have to review my ball changing technique and see if I can come up with a better way to do it.

    I tried to get Michael Dubno's RPi software working at the Faire and couldn't get it to run properly- I'll be revisiting that in the next few weeks because it generates really nice patterns and has a bunch of other great features and capabilities.  The problem seems to be in the communication between the RPi and the smoothieboard.

    I may redesign the motor mounts to allow NEMA-17 motors to be used and may switch the controller to a Duet board or one of the others that uses 256:1 ustepping drivers to reduce the noise level from the mechanism.

    The magnet sliding against the plywood creates some very fine dust that tends to accumulate on the X axis guide tube and can jam up the motion.  I had redesigned the magnet carriage with large holes to allow the sand to fall out, but I'm going to look at redesigning the X axis, milling a UHMW shoe for the magnet, and maybe applying a coat of polyurethane to the plywood to minimize dust generation.

  • Converted to stacked belts

    Mark Rehorst09/17/2018 at 17:09 0 comments

    There was too much belt wear at the corner pulleys due to the twist in the belts, and where the belts contacted each other at the twists, so yesterday I converted the mechanism to stacked belts.  I also installed some LED strips with 60 5050 LEDs per meter.  I'll be updating the CAD files with new details.  

    The new lighting uses red and blue 12V LED strips with buck converters to drive them from the 24V power supply.  I can adjust the voltages on the converters to control the relative brightness of the lights.  The LED strips are mounted on pieces of aluminum L stock to act as heatsinks and make it impossible to see the LEDs directly.  The way it is lighting the table is exactly how I wanted it to look.

    I recently made a tool to level the sand - just a piece of wood with screws near the ends.  I push the tools down until the heads of the screws are contacting the plywood, then just pull it across the table to level the sand.  I've done some experiments with the depth of the sand and it seems like having 1/3 or less than the ball diameter seems to work well and guarantees that the ball won't get stuck.

    The video doesn't have the contrast that the table has when you looking at it- the shadows are much darker so the red and blue really stand out.

    The mechanism seems to be finished from Mark Rehorst on Vimeo.

  • Installed LEDs, generated more patterns

    Mark Rehorst09/10/2018 at 01:39 0 comments

    I spent a lot of yesterday generating patterns for the table to run at the Milwaukee MakerFaire.  I ended up with about 30 different patterns and put them together into one gcode file.  It takes 2-3 hours for the entire sequence to run (at 500 mm/sec) before the patterns start repeating.  I put 6 copies of the sequence into the file, so I should be able to leave it running unattended at the MakerFaire.  I added a 60 second pause after each pattern is complete so people could admire it before the table starts overwriting it with a new one.  

    Someone at the Makerspace pointed out that when the machine stops running for 1 minute, a lot of people will walk away, and then when it starts running again, a new crowd will be able to get a good look at it.

    I installed some COB LEDs, blue on one side and red on the other.  Unfortunately, after about 10 minutes the red ones ran so hot they started burning up.  I'll be shopping for more LEDs tomorrow.

    I also tried running with a 15 mm ball instead of the 1" ball I was using.  It seems to go all the way to the bottom of the sand and leaves narrower tracks so the patterns appear sharper.  Here are a few more teasers:

    15 mm ball on sand table from Mark Rehorst on Vimeo.

    circles with 25 mm bal at 500 mm/sec from Mark Rehorst on Vimeo.

    Some of the nicest effects come from the patterns overwriting each other, especially when there are gaps between the lines in the new pattern.  

  • New patterns, more speed

    Mark Rehorst09/08/2018 at 03:33 0 comments

    I generated a bunch of patterns using sandify today.  The plan is to stack a bunch of patterns in a single gcode file and let it run on the machine during the Milwaukee MakerFaire, so that I can hopefully leave it unattended.

    Sandify shows where the patterns start and end using green and red dots.  I generated a bunch of patterns and initially put them into file folders labeled with the side of the table where the pattern starts.  Each file was named for the basic shape and where it ends.   I then made a list of patterns, starting with a wipe to overwrite whatever was on the table with parallel lines.  That pattern ended at the top right corner of the table, so the next pattern chosen started at the right side of the table and ended on the left side.  The next pattern started on the left and ended at the center, etc...  I stacked all the gcode in one file and then set a speed parameter with the first move command.

    I tested speed and acceleration in addition to generating patterns.  I pushed it all the way up to 500 mm/sec with acceleration at 1000 mm/sec^2.  I was very surprised it could run this fast- I was expecting for it to run at 30 mm/sec or so.  I may push it higher still...

    sand table 500 mm/sec test from Mark Rehorst on Vimeo.

    more 500 mm/sec from Mark Rehorst on Vimeo.

    The LEDs arrived today, so I'll test them tonight and mount them in the machine tomorrow.

  • Fusion360 CAD Files for table design

    Mark Rehorst09/07/2018 at 01:55 0 comments
  • Today I changed the pulleys

    Mark Rehorst09/07/2018 at 01:37 0 comments

    I was using stacked F623 bearings for pulleys, but found that the flanges weren't large enough and the belt kept climbing up on them which was starting to wear out the back sides of the belts, so I got some similar size pulleys with larger flanges and installed them today.  Luckily, there was room for the larger flanges in the printed parts of the mechanism and I was able to just drop them in.  Now the belts stay where they are supposed to.

    A motor and Y endstop
    Electronics enclosure mounted on leg brace
    Two patterns
    Whole table with two patterns

    one more test video, increased speed from Mark Rehorst on Vimeo.

    Cardboard guard on underside of mechanism
    Corner pulley block with new pulleys
    Y axis slider with new pulleys


    Tonight's project- generate more patterns for the 1" ball (in the photos and video) and generate some for a 15 mm ball, too.  I'll try to make a tool to level out the sand.  Tomorrow: testing for speed and acceleration using the new patterns.

  • First test with "sand"

    Mark Rehorst09/05/2018 at 03:04 0 comments

    i was able to test with "sand" today- it works!  The "sand" is sodium bicarbonate blasting media from Harbor Freight Tools- a 50 lb bag was $32 with a 25% off coupon.  It turns out I only need about 25 lbs of the stuff on the table.

    I still have to play with it to determine the optimal depth of sand and then test speeds and accelerations.

    First test of sand table with sand from Mark Rehorst on Vimeo.


View all 9 project logs

Enjoy this project?

Share

Discussions

Jeffeb3 wrote 09/06/2018 at 21:11 point

Sandify!

  Are you sure? yes | no

Mark Rehorst wrote 09/07/2018 at 00:57 point

been there, done that!

  Are you sure? yes | no

Ryan wrote 09/06/2018 at 16:59 point

You should try baking soda. It gives really sharp peaks and is less "crunchy", very little grinding noise as the ball gets dragged through it.

  Are you sure? yes | no

Mark Rehorst wrote 09/07/2018 at 00:55 point

I used baking soda...

  Are you sure? yes | no

Ryan wrote 09/07/2018 at 01:20 point

I assumed blasting media was more coarse, sorry. My peaks are much crisper for some reason with arm and hammer.

  Are you sure? yes | no

ken.do wrote 09/06/2018 at 13:32 point

How does your 'sand' react to black lights?

  Are you sure? yes | no

Mark Rehorst wrote 09/06/2018 at 14:03 point

It reflects it (lights up blue) but doesn't fluoresce.  I'll be experimenting with adding chemicals to make it fluoresce over the next few weeks.  I'm not sure that fluorescence is desirable for this- if it fluoresces there won't be any shadows and that will make the patterns in the sand less visible.  I'm planning to light if from a low angle in red on one side and blue on the other to create shadows that enhance the appearance of the patterns in the sand.

  Are you sure? yes | no

ken.do wrote 09/07/2018 at 00:11 point

That lighting sounds cool. In 3D...

  Are you sure? yes | no

Mike Szczys wrote 09/05/2018 at 15:35 point

This came out great, well done! Now I really need to make sure I make it to Milwaukee Maker Faire this year to see it in person.

  Are you sure? yes | no

Mark Rehorst wrote 09/06/2018 at 13:59 point

Thanks, but it isn't quite finished yet.  I'll be adding red and blue LEDs in a few days, and have some other tweaking to do.  I'll see you at the MakerFaire!

  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