Harsh Mistress

Photo-Kinetic Sculpture based on the Robert A. Heinlein classic “The Moon is a Harsh Mistress”

Harsh Mistress sculpture – background data

Mare Crisium on Luna’s north-east quadrant (upper right as seen from Earth) is the principal setting of Robert A. Heinlein’s classic novel “The Moon is a Harsh Mistress”. This sculpture is based on a Lunar Reconnaissance Orbiter image with LEDs highlighting places mentioned in the novel. The LED locations are a best guess based on repeated careful readings of the source material. The sculpture measures about 970 x 570 mm, designed for wall mounting.

The entire sculpture is close to real scale. The curvature of the moon’s short horizon is obvious. The major item that is not to scale is the launcher. It is about twice as long as described in the novel. The location of the LuNoHoCo launcher is a guess, based on deliberately vague mentions in the novel. The locations marked by LEDs are: Lunar Authority (blue); Luna City (red); Crisium Spaceport (white); Tube Station West (orange); Davis Tunnels (green); LuNoHoCo (yellow). Each of the LED colours is biased in the specified shade, but has a pseudo-random variation. The name of each location is displayed in Morse Code.

The Launcher brass housings also act as touch-sensitive controls. Brightness and speed can be controlled within narrow parameters. The LEDs can be turned on or off, although the circuit always runs when power is applied. There is a mounting option of an internal battery bank. Current draw varies from 20 – 50 mA. A 2600 mAh battery will run the circuit for almost 2 days. Choice of battery bank is important. Since the current draw is so low, most battery banks designed for phone charging will shut off due to their power-saving feature. The best long-term display option is the provided USB wall charger.

The core of the Harsh Mistress sculpture is MDF, laminated from standard sheets. 16 hours of CNC machining produced the 3D surface and the cavities on the back. Multiple layers of epoxy consolidate, protect, and smooth the MDF. Metallic tints provide the background and the feature colour highlights. The control circuit is an Arduino Nano with custom code. The lights are AdaFruit NeoPixel individually addressable LEDs.

The Harsh Mistress sculpture is unique. There will not be any copies or reproductions. It will make a fine addition to any collection of Robert A Heinlein memorabilia.


“Harsh Mistress” is complete. It was a six week project. My intention was to start “Galileo” next. However, Rob Sawyer generously invited me to a Patreon-only party at his home. I mentioned this project to him, and my plans to eventually do a similar piece based on “Land”, the continent on which his trilogy of the “Quintaglio Ascension” is set. I asked for his permission to use one of his maps as the basis for a sculpture, to which he readily agreed. My work sequence changed after I got home. There is an off-cut of MDF from “Harsh Mistress”, which is perfect for a smaller version of “Land”. “Galileo” will come later.

This item is for sale in the Fabrikisto.com store.


Harsh Mistress done

Harsh Mistress is done. I immediately moved on to “World”, the inhabited moon of the Quintaglios.


Harsh Mistress on wall

There were a couple of “What was I thinking (or not)” moments in mounting this piece. First, it turned out the mounting slots didn’t have the undercuts. I took care of that with a hand-held palm router. I have no idea how that happened. Second, the entry/exit holes for the mounting slots were spaced such that it was impossible to engage both mounting screws on the wall. A drill took care of that. Then it worked as designed, with the wall screws in the slots, allowing quite a bit of horizontal movement for alignment.

I’ll take archival and promotional images and videos later this coming week.


Final coat epoxy on Harsh Mistress

The Harsh Mistress sculpture is done. It just needs a couple of days for the final epoxy coat to fully cure. I applied a full clear coat, then using smaller brushes added 8 different colours in semi-random locations. I concentrated most of the colours on craters and crater walls, spreading and slightly blending in those areas using disposable acid brushes. Along the dorsa in the mare I sprinkled colours from a wooden stick, then stippled them into the epoxy with a small artist’s brush. The epoxy was already gelling at that point.

Now I leave it for a couple of days. I have a wall location in my office in mind, so it will be prominent when anyone walks into the room.


Harsh Mistress all lit up

Getting the test circuit moved to the sculpture proved to be a bit challenging. The proto boards did arrive on Tuesday. They are a brilliant idea, one of those that when you see it, you wonder why someone didn’t develop it decades ago. However, my ancient soldering iron’s tip was quite eroded, to the point where the point was several millimetres across. This caused some bridging on the narrow traces. I eventually removed the tip, ground it down, and successfully removed the bridging.

The next challenge was more a case of requiring patience than talent. This afternoon I got the wiring between the components all done. Everything worked on the first try. The only unusual thing is that the touch sensitive brass contacts are responding differently than what I programmed. The On/Off should be the outer guides, in practice they are second in from the ends. The end contacts are controlling the speed. I don’t know yet why, but everything works. I have the circuit running on the battery pack, although I provided for a USB power connection.


Harsh Mistress cleaned up

Today I made good progress. Trimming the piece from the surrounding MDF blank only took a few minutes, and sanding the perimeter down took only a bit longer. After thinking of various ways of suspending the piece while working on the various aspects, I decided to keep it simple. I drilled 16 mm holes at four points on the perimeter, and inserted dowels. They will be stored in the back cavity when not in use.

It was only early afternoon so I kept going. The individual LEDs are now all wired and inserted in their proper locations. I was lucky with the 6th one – it’s not visible in the photo, and represents the “secret” location of the LuNoHoCo launcher. Once the piece is complete and the LEDs are running, it’ll be obvious.

Next is wiring the circuit. I have some proto boards on order from PiShop.ca. They should arrive Tuesday or Wednesday. Once the circuit is tested and working I’ll apply the colours.


Another epoxy coat

There are now two layers of EcoPoxy FloCast on the back and three of UVPoxy on the front. The FloCast is a slower-setting blend, intended for deeper pours. It’s what I had. It has very low odour. The UVPoxy I picked up a few days ago is much more viscous, has a shorter set time, and stinks. So this morning I picked up a 3M mask intended for mild organic vapour exposure. It works, and is fairly free-breathing.

At first I thought that the higher viscosity of the UVPoxy would be a problem, but now with the third coat on, perhaps it is the better choice. Next will be a clear coat with hand-applied colours to highlight craters and other features. Everything so far, from the original topographic image to the colouring, has been as accurate to reality as possible. The colours will be purely artistic.


Harsh Mistress machined

Two full days of running the CNC and dust system later, the 3D machining is done. Total time was about 16 hours. It would have been much longer, but after letting the fine detail toolpath run for a while I decided to terminate it. The MDF doesn’t support that level of fine detail. Instead, I re-machined the medium toolpath with a 1/4″ ballnose cutter, set about a half millimetre lower than the first time.


Harsh Mistress underside

After an exciting and stimulating weekend in Mississauga, I’m back to work on Harsh Mistress. Today I machined the underside of the sculpture. That only took about 2 hours. The 3D work will take much longer. I plan to start that tomorrow.

The main cavity will hold the LED wiring and the Arduino Nano. The narrow channels are sized for a USB cord, allowing access from all edges. The two slightly slanted grooves are keyhole slots for mounting on wall-mounted screws. The are spaced for either 16 or 24″ OC.


Launcher parts

The vertical supports for the launchers look a bit out of proportion, but with anything smaller diameter the LEDs would not have fit inside. Even with these, it was a tight fit with all the wires, especially the ones attached to the brass tubes for touch sensing.


Launcher Modules

This is a part of the project I was not looking forward to. It turned out to be a half-day project, but it turned out to be relatively stress-free. The key was to make a jig for each part in the sequence. The first jig was to hold the cut-off tool so I could rotate the brass tubing for a clean cut. I cleaned up each piece, both longer and shorter, on the lathe using sandpaper in 2 grades. The second key was another jig to hold each short piece for cross-drilling. That required a fitted dowel inside the brass tube to prevent the tube from collapsing, and allowing a clean hole. I then used that same dowel to hold each assembled piece for soldering. I heated each assembly with a blow torch before applying solder to each quadrant. The last part was to sand and polish each assembly after it had cooled.

Each assembly will be mounted in the “launcher” pattern with a programmable LED at the junction. The light will reflect inside the horizontal tube, producing a sequential light show.


Harsh Mistress lights breadboard

I’m learning Arduino programming. The circuit and software in the image above is the interim result of a week’s work. The microcontroller is an older Arduino Nano. The connector is a bit flaky, so I ordered several more. In that process, I found that the Raspberry Pi foundation now also has a microcontroller, the Pico. That one runs on C or Python, the Arduino on a proprietary language modelled on C. If I didn’t already have the Arduino and was starting from scratch, I would probably have used the Pico. However, the ecosystem, particularly add-in libraries, for Arduino is much more mature.

I now have 5 Arduino Nanos and an Uno, and 4 Raspberry Pi Picos. Given that they run between $6.60 and $16, it’s not a big deal if I damage one. So far they’ve proven to be robust.

In the photo above I’m doing a battery run-down test. The small flashlight/power cell is rated at 2600 mAh. It’s been running for almost 9 hours. At this rate a fairly standard cell phone battery bank could run this circuit for several days. If the test runs successfully for 24 hours, I’ll get a good battery bank and power this circuit with that, not worrying about a wall power supply.


I also successfully uploaded an Arduino sample file to the breadboard circuit for Harsh Mistress. I had to revert to my old Surface Pro 3, since my Surface Book wouldn’t recognize the Arduino Nano. The sample file works great! Now I can start modifying it to give the patterns I want for Harsh Mistress.


Harsh Mistress Simulation

Here is the result of several iterations and days’ worth of work on this concept. Mare Crisium on Luna’s north-east quadrant is the principal setting of Robert A. Heinlein’s classic novel “The Moon is a Harsh Mistress”. This sculpture will be based on a Lunar Reconnaissance Orbiter image with LEDs highlighting places mentioned in the novel. The LED locations are a best guess based on repeated careful readings of the source material. The sculpture will be about 970 x 570 mm, designed for wall mounting.

The next step in the process is diving into Arduino programming for the LEDs.

By the way, I have a Patreon profile, which is a simple way to support my efforts.