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Refining the Formula

I was invited back to the science museum to do something cool with my machines. Any time I do a public event it’s an opportunity to figure out what’s engaging and do better the next time around.

I was maybe a little too motivated and brought several machines, almost my whole apparatus, and deployed them in various modes. 1 PewtyBot, 1 Mirror PewtyBot, 1 PlottyBot & 1 SkecthyBot doing portraits, and 1 PewtyBot people could control with their phones. The laser portraits worked wonders again, but the original PlottyBot drawing post-it portraits worked even better.

People were clearly keen on getting a tangible souvenir from the evening. Having a robot draw their portraits on a Post-it note struck a chord hard. I think what I’ve learned from this event is that while the lasers throw a lot of pazzazz at you, they are more complex machines that most people don’t try to engage with beyond taking in the light show. While a pen based machine is doing the same thing you’d do with your hand so it’s more approachable to be curious about. As usual a small fraction of them were fixated beyond reason on watching the machine at work. There has to be a “drawing automaton obsession” gene present in ~10% of the population.

Unfortunately, I only had one PlottyBot doing the Post-it portraits, and they take much longer than the lasers so I spent much of the evening trying to keep track of a queue of people who wanted one.

I built 2 4’x4′ photoluminescent paper holders so I could deploy this easier. In the past, finding a decent spot on a wall for the rolls and unrolling them was difficult and time consuming. I also have plans for doing random outside events at dusk in random places this Summer, which is why having something deployable was worth the construction effort. I tried it some already at home last Summer and it’s kind of cool to have the lasers go on a warm Summer night.

I had several people ask me if this was AI :), this seems to have become the go-to explanation for anything tech based that can’t be explained easily. Much like Clarke’s law that “Any sufficiently advanced technology is indistinguishable from magic”, only now it’s AI instead of magic. I’d respond that it was just good old organic grain-raised free-range “I”.

As usual, it was very hard to capture the coolness while manning it so I don’t have much visuals to represent what went on. Ultimately it’s just me running 5 machines, a software stack and talking a lot. Suffice it to say people were into it and I’m emboldened to keep trying public events. Fun times!

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Fancy Meerers

The mirror based PewtyBot proved conclusive enough but since the laser is reflected twice, a degradation is clear on the medium if the mirrors aren’t high quality. Clearly the cheap plastic ones I got to test with aren’t, but they served their purpose. With much research on mirror specs & bounding agents, I went ahead and spent $70 on two tiny “surface first enhanced aluminum” mirrors. Once again, I forgot everything about my high school physics lessons, but some vague notions are left to help me navigate through specs. And this being 2026, of course there’s a website dedicated to optics of all sorts I can buy any sort of mirror from. The modern world has its flaws, but access to information and stuff is definitely covered.

These new fancy mirrors are extremely crisp. Unfortunately, one of them slid on the epoxy as it cured, this won’t impact use but I’m bummed for I really did all I could to get everything perfect.

I tested the upgraded machine and it performed just as well as before, but the laser pointer was pristine as it hit the medium. This might not be a $70 improvement, but if I’m going to build a machine it’s hard to leave it lacking. The kids have been curious about this new development, it’s always fun to see the gears turn when they engage.

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Overcoming Inertia

The design of PewtyBot 1.0 left something to be desired: the whole top section (stepper motor, assembly & laser) is moving, and that is a decent amount of mass that needs to be accelerated rapidly many times over.

As I was tuning parameters, it became obvious that I needed to slow things down to avoid inaccuracies from the vibrations of a fast accelerating mass. I found happy parameters which led to several public deployments, but deep inside I knew I wanted to try the mirror approach. Instead of moving the laser, it remains static and only a couple of light mirrors are doing all the moving.

Introducing PewtyBot 1.1!

There’s a funny story in there about losing code, reimplementing, and a core issue I was struggling with being solved without knowing why. As always, a few unforeseen challenges got in the way, but ultimately the math is exactly the same as PewtyBot 1.0 so that was a relief. It’s just the motion code that needs to be adjusted some to deal with mirrors.

And well the results are cool, but somewhat mitigated. Definitely not “rocks your socks off” levels of cool. I can definitely move the laser a lot faster. Although through the exercise, I’ve realized that the “slow” speed of PewtyBot 1.0 may have been in the perfect sweet spot for laser light retention on a photoluminescent medium. And so maybe I got lucky there. Of course I could get a beefier laser that emits more light to compensate for the reduced time it spends on any particular area. I’m pretty convinced though that I want to remain in the “cat laser” realm for risk & safety. And so the other variable I get to play with is mirror quality, and I shouldn’t be surprised that there exist a whole world of mirrors of various specs. I got some very cheap craft type acrylic mirrors at first to test concepts. But you can tell the pointer hits the medium diffused and discolored. And so ultimately I’ll want to spend the money on a few square centimeters of first surface mirrors rated for blue light wavelengths. But first I’d like to convince myself that the mirror approach actually brings something extra to the table.