A 450mmx850mm Sand Table

I am building a 450x850mm (addressable area) non-ZenXY sand table to replace my coffee table, which is worn out and decidedly non-robotic. How about some Robert Frost?

Since the mechanism is cool, I’ve put it above the sand. But it would be easy to flip over if that was your thing.

The non-rolling ball is a little bit noisy as it grinds through the baking soda. I wonder if it could be suspended very slightly above the plywood base, if it could be spring loaded or made lighter, or if the base could be damped or lubricated so that the machine could be quieter.

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Removing noise is hard. What does the mechanism look like? Maybe the surface under the soda could be thicker?

If the ball is not rolling, could it be replaced with a stylus?

Might be fun to try a controlled rotating “pen nib” and do calligraphy.

The first thing I put in the 12mm cylinder tool holder was a AAA battery. It clears out its narrow path unlike the ball that creates a wider eased trough. Something like a polyethelene sheet on top of the plywood might quiet it down. See also UHMW sticky tape which makes a great bearing surface.

I would love to route power to the tool but it would be a tight fit since there will be a table top.

A thicker base is a good idea.

This box is a plywood skirt with a groove to capture the thin base.

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Video: https://www.youtube.com/watch?v=VV8uPtPWkMw

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That is a very neat design. I actually really like seeing it (because I am a nerd, and that’s ok). The stylus is “passive” because you don’t want any wires headed there. I think that kind of constraint actually makes this sand table design thing more appealing. Problems lead to solutions. I wonder if the gantry being visible would hurt if you were trying to sell this as a product, but since it’s for yourself, and you obviously like working on mechatronics, it is appealing.

So those side blocks are riding on strips of plywood, and that is your “linear rails”? And then the middle is some 1010, I’m guessing (or 2020, it’s hard to guess scale).

I imagine that if you reworked the gantry part to make it a tad thinner, then you would be able to see it just a little better.

I also like that the belts are pulling against the plywood frame, instead of screwed into the surface, and using the plastic and the screws to keep it straight. There are a lot of neat tricks in this build. Thanks for sharing.

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Looks like a very small BOM, Slick Idea for sure.

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I’ll have to try a hockey-stick shaped uncontrolled nib, or a paintbrush.

You have to wonder about the market for “robotic tables for non-nerds”…

It would work better thinner. There would be less torsion on the rod.

I’ve realized this design has the option of suspending the stylus above the plywood so that it never touches. Just add a little more sand. Then the machine would be very quiet, with the grinding noise no longer overwhelming the motors’ slight hum.

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Ummm… Not gonna touch that one (without sani-wipes)… :peach: :gear: :eggplant:

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Good point. These should belong in common spaces like living rooms or office waiting areas, or bars. I would hope the appeal is greater than the few percentages of people who are engineers or the few more that self identify as nerds.

You’ve probably noticed that the steppers rapidly lose torque after they hit a speed limit. They have a lot of torque when running slow and no torque when running fast. Mine seem to max out at about 10,000 pulses / second with x16 micro-stepping i.e. 625 full steps per second. I tried replacing the initial 20t drive pulleys with 40t and 30t pulleys. It runs fastest with the 30t pulleys, but with the 40t pulleys the additional torque required gets about the same (reliable) max speed as the 20t pulley. Runs around F7000 with the 20t/40t pulley and F10000 with the 30t pulley. It can run faster than that for a bit, but then it’ll skip steps when it runs into a rougher area of the table or perhaps when it heats up.