My Coffee Table is a Robot – The Sand Plotter

Apparently I didn’t write this one up already. Here’s a build from a couple of years ago:


It’s a coffee table with a bed of sand, and underneath is a CNC plaform and a powerful magnet to drag around a stylus and make patterns.

The hardware is pretty straight forward. I bought a coffee table from Ikea and mounted a wooden frame underneath:


Then mounted the CNC gantry under that: IMG_7311.JPG

I spent a while troubleshooting the motion. Nick and I both made tables previously, and the secret seemed to be having a soft base underneath the sand, and also using a cylindrical disc magnet rather than a ball.


Spherical magnet made the pattern on the left, and a disc magnet mad the circles on the right

This is to minimize the amount of ‘uphill’ work the magnet has to do. A cylinder is just dragged through the sand horzontally, whereas a sphere tends to jump and skitter irregularly, which is bad for both the smoothness of the pattern, and how pleasing the sound is to hear.

Coffee Table v01.JPG

It has a glass top, but we removed it some of the photos.

Here’s it in the Powerhouse Museum, briefly brought in for a photoshoot before Maker Faire a couple of years ago. That’s right, something I made belongs in a museum😀


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Standing Desk & Aluminium Extrusion

I recently got a bunch of aluminium extrusion so that I can rebuild the Turquoisebot in a more accessible way.


I’ve used OpenBeam before, but not 8020 style extrusion. As a quick test project, I decided to make a standing desk addon for my work table.


“Before you cut firewood, sharpen the axe.” 


I noticed the metal bandsaw was cutting atrociously, so I spent an hour re-aligning it & testing out the tension and perpendicularity.

IMG_1624.JPG IMG_1625.JPG

Not perfect, but at least the right angle joints didn’t fail the laugh test when I put them together.


Cutting the lengths


Completed stock

Some assembly later:


The completed table

It should be at the right height to have my elbows perpendicular while standing & using the keyboard.

As a construction method, I’m amazingly happy with it. I have an extremely sturdy frame, and it was very quick to put together. Moreover, if I change my mind in the future I can reuse all the parts easily.

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Cause I’m a Rocket Lamp….


This was inspired by a pic, of a screenshot, of a photo sent to a friend of mine. No idea where the original came from. (If it’s you I’d love to give you credit).

I couldn’t resist immediately going out and getting a Saturn V kit after dinner, and finished assembling it at 2am. Next day I started on the wiring and assembly of the base. Completely rushed and I’m not going to impress any actual modellers, but hey.

Rocket Lamp

It’s just under 2m tall.

Lights are Neopixels and a quick sketch to make them flicker and flame.

rocket lamp 2

Edit: There’s been a few people asking for details of construction.

The base is a wood block with steel threaded rod for support. Unfortunately I didn’t have joiners, so had to use two rods and cable tie them together to get the length (Did I mention this was a rush project?)

The cloud material itself is polypropylene pillow stuffing. I went to Kmart and picked up their cheapest pillow that mentioned polypropylene for $5. I have about half left over.

This site here has a much more detailed writeup on making ‘cloud lamps’, which is how I got into this in the first place.

Edit2: Thanks to Reddit user Dschull for this photoshop:

Rocket lamp in space.png


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Restoring an unusual vintage clock display

I had a good find a few months ago when I picked up that rack for holding my time goodies. It’s an old bulb display unit for showing the time.

Before we had LCDs, TFTs, and even LEDs, there were very limited options for displaying information electronically. One way to do it was decatrons, but the tiny neon glow they create is impossible to read from a distance. Mechanical displays are another option, but they are noisy and unreliable.

The solution this manufacturer used, was to make a projector, using an incandescent bulb, photographic mask, projection lens, and frosted glass display:

Bulb display sketch - single v01

Actually it was a bit more complicated, since each display must be able to show multiple possible digits, there were 12 bulbs, 12 masks, 12 lenses per screen.

Bulb display - group v01.png

Which, for a clock showing HH:MM:SS, means 72 light bulbs to replace.

I didn’t fancy restoring a clock only to have it blow again, so I decided to replace the bulbs with LEDs.


I played around a bit with the colour temperatures. On the left, the ‘1’ is displayed using the original bulb, on the right the ‘8’ is using a cool-white LED.

I decided that a warm colour was more in the original spirit of the clock, so I did a bulk order of warm white LEDs, and started replacing the bulbs.

In order for the projector to work well, the LED must be in the exact position of the old bulb. I lasercut some jigs to hold the LEDs in place, and glued the wooden pieces into the frame.

Afterwards I ran horizontal wires telegraph-style between the digits, and made a multiplexed setup with common-anodes for each digit.


I used an arduino with a $5 RTC module as an accurate time source, and programmed it to display on the multiplexed LEDs. (Later I’ll hook it up with the Rubidium atomic standards as the time source, but for now it’s more than adequate).


Here’s what the final result looks like:


I’m very happy with it. The crispness of the digits is something that’s almost unheard of with modern displays. Check out the points on the ‘5’, they could take your eye out.



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Home ‘Supercomputer’ using spare raspberry pis

This project was inspired by James, who was inspired by Dave from EEVBLOG:


It’s a lasercut rack to hold all the Raspberry Pis I could get and make them do distributed computing. (Rather than the standard application for a raspberry pi, which is to sit unused on your shelf)


I was able to find four spare pis at home (see?), and scrounged up another couple from friends. The tricky part was making a caddy that could hold all of the different models (some of which lack screw holes) and allow for easy removal, and also making sure all the connectors were exposed while in the rack.

A network switch is bolted to the back, which avoids too much mess with cables. There’s a separate power switch for each unit, so that the whole cluster doesn’t have to be taken down to change one board.

After playing around with spreadsheets and running some tests, I’m of the opinion that this cluster running all year couldn’t match my macbook running full tilt for a few weeks. However per watt it’s actually not that bad. Dave goes into the numbers much more. 

Files are up on Thingiverse if anyone wants to make their own:


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Phi-lipers – Golden mean calipers

No more needing to argue about whether a particular design is ‘golden’ or not. Measure it and know that it isn’t!



Files here:


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Stepper test box

So many devices we work on have stepper motors in them. It occurred to me that it would be handy to have a device to allow quick testing of whether the motor was working or not.


The user interface is really minimalistic. A switch selects whether the motion is continuous or step-based, and there’s one button for forward and another for reverse.


Quick and dirty, but I wish I’d had this years ago. It would have taken the guesswork out of troubleshooting so many things…

Files here:


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