A new, smaller version of The Spice Must Flow with servomotors: Arrakis

I’ve started building a smaller version of The Spice Must Flow to use as a coffee table. I haven’t chosen a name for it yet. This one is 120cm long x 83 cm wide, with glass top. The mechanism is being kept near the floor so the top can be higher above it and hopefully not require as frequent cleaning as the original. I am using the same 45 mm square t-slot for the frames.

electronics

I have built the top cover and XY frame, and mounted the electronics. I am in the process of remaking the cables to the motors (MUCH shorter now) and redesigning the Y axis bearing/pulley blocks to be similar but a little less fragile than the previous generation. I printed one of them and will print the other tonight. The new bearing block is printed in two pieces without support material and clamps down on the 16 mm square tube X axis. I hope to have the mechanism up and running by this weekend, and then I’ll start on the new sandbox design.

One thing I’m currently stuck on is making the electrical connections to the LED strips in the sandbox. I’m going to try to set it up so that there will be contacts on the frame and on the sandbox and when you set the sandbox on the frame the connections will be made automatically- no loose cables, no connectors. I’m thinking of using magnets mounted on springs to allow some lateral error in the placement and the connections will find each other without any manual intervention.

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I think for my next one I am going to try and mount everything in one corner so it could be hidden in a leg or something. The only other options I can up with is a folding tray like you have so it is easy to work on and then fold it up and out of the way 99% of the rest of the time.

Have you seen “spring test probes”? They would work well for making the connection to the lid for the lights. You could still put magnet or two nearby to make sure they align with the pins.

In my design, no local control panel is needed, so the electronics stays under the sandbox, out of sight. I use a Duet wifi enabled controller running as an access point so I can connect to it via my laptop or phone. I can even have it load a macro that calls pattern files on power-up, so if I take it to a public showing, I just set it down and power it up and it will start running patterns.

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Yeah, I’m aware of those. I’ll have to do some experimenting…

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What is that? Like those things that happened in 2019?

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No motion yet, but I have almost all the mechanical work done on the mechanism. I have to mount the endstops and then I should be able to test it, hopefully tonight or tomorrow.

Business end of the mechanism with electronics and assembled X axis. There are two power supplies, 150 and 200W, a Duet WiFi controller with expansion board, and of course, two servomotors.
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Magnet carriage- the magnet will be glued to the top using silicone. The blade(s) will be used to trigger optical endstops.
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One of the two Y axis pulley blocks. Both have PTFE bearings that slide in the t-slot - one is screwed to the block, the other is mounted on pins and spring loaded. The blocks are printed in two pieces and the screws that hold them together clamp the X-axis tube between them.
Google Photos

Once it is working to my satisfaction I’ll get started on the sandbox. I’m considering covering the bottom of the sandbox with metal foil and grounding it electrically so the sand won’t accumulate a static charge that will tend to make it stick to the glass top.

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How much torsion does the Y axis pulley exert on the slot? Any reason for PTFE instead of UMHW this time?

The Y axis pulley on the other end of the X axis twists the whole thing the other way, so there’s probably not much net torsion. Of course the X axis tube is being twisted, but it doesn’t seem to mind.

I was out of UHMW and happen to have a big brick of PTFE.

It’s all assembled but the motors aren’t spinning yet. I have some troubleshooting to do. One of the endstops is not working properly so I ordered more of them and should have them on Sunday.

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It’s running, and very quiet at lower speeds. But, or course, it can go super fast, too, with a bit more noise.
I had some problems with the controller board that are mostly sorted out now.

Arrakis test video #1
Arrakis test video #2
A tour of the Arrakis mechanism while it runs very quietly at 200 mm/sec.

Next step is to decide on the LEDs and make the electrical contact pads on the frame so the sandbox can just drop onto them. I may go with some RGB LEDs so I can change the LED colors to suit the mood or season or pattern. They will not be flashy and cycling while the machine runs- just static two colors or white. I’m trying to figure out if I can use some of the PWM fan outputs on the controller board to drive the LEDs.

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The sleeper has awakened! Please release your STLs so we may learn the weirding way!

I’ll do better than that- I’ll post a link to the CAD file. The STLs wouldn’t be of much use because they are specific to the hardware I used, but with the CAD file you’ll be able to modify my designs to fit your hardware. I’m using Fusion 360 to model everything.

The t-slot frame is 45 mm square with 10 mm slots (Bosch?), not a common size, I think. The X axis tube is 16 mm square. All that stuff came from a local scrap yard. The springs on one of the Y axis bearings came from a box at the makerspace. I don’t have any part numbers to order that stuff, but if you’re reading forums like this you probably don’t need a BOM and can modify the design to suit whatever hardware you have.

One thing I haven’t tested yet is whether the magnet will interact with the X axis tube and create drag on the mechanism at high speeds/accelerations. It didn’t seem to be a problem in the previous design, but I think the magnet was further from the tube.

This is what the magnet carriage looks like inside:

In the photo, the printed part on the X axis tube is the top and the other printed part is the bottom. I quickly realized that was going to be an assembly nightmare, so I changed it so the screws come up through the bottom part and screw into the top part (which means they want to fall out of the holes while you’re trying to assemble it…). I switched to a single endstop flag and moved it to the top piece as you can see in the videos. There are four 13 x 30 x 5 mm PTFE bearings fit into slots in the top and bottom pieces, and I control the pressure they apply to the X axis tube by shims cut from a beer can. Even with the changes, assembling the carriage is a little tricky because of the way the belts have to be looped around the screws. Having 3 hands would help…

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