World’s Smallest? I’m not sure, but it’s definitely smaller than any other “Useless Machine” that I’ve seen so far*. I’m sure a tinier machine could be built, so if you have one, be sure to let me know in the comments. To explain things, here’s a video of it in various experimental stages:
If you’re not familiar with the “useless machine” concept, you flip a switch, and it turns itself off. Clever idea, but not mine originally.
This model was very much done “free-form” I had a general idea of what I wanted to do (build a tiny useless machine using a sub-micro servo and ATTiny chip), but I didn’t draw any CAD models. I just cut as I went with my milling machine and Dremel tool. Photos at different points in the process are after the “read more.”
As you can see, the results are quite shoddy, but as an engineer, it was refreshing to make something without all the details worked out. OK, maybe that’s what I do a lot of the time as an engineer, but at least there was no pressure to get it done and working correctly this time!
Most “useless machines” use a DC motor, but this one uses a sub-micro servo (like this one from Amazon) and an ATtiny chip (my introduction to this cool little chip), to cause a “finger” to pop out of the box and turn itself off when disturbed. Here’s the code, I’ll go over more details of controlling a servo this way in an upcoming post). As seen in the video, I don’t have this totally perfected yet, but I hope to eventually make a better one, possibly with my CNC router and a few pieces of MDF.
The electronics of this machine consist of 2 CR 2302 batteries (super-cheap from Amazon) stacked in series to provide roughly 6VDC to power the servo and ATTiny chip. There’s only one input. When the switch turns on, the servo pops out until the switch is no longer on. One input, one output. A 10KOhm resistor is used to pull the switch to ground so the input doesn’t float around, and the perfboard keeps everything relatively neat.
One “unique feature of this tiny “box” is that the 1/8 inch polycarbonate top door was drilled to accept a pin meant for sewing to act as a hinge. This worked pretty well, but I had to be very careful with the drill bit to make this bearing surface. I’ve got some ideas on how to improve this in the next iteration, so be sure to subscribe (upper right on this page) so you don’t miss anything!
If you found that interesting, you might also check out my “mechanical useless machine prototype.” It’s more or less the same concept without any electronics.
*If you want to know the actual numbers, This little prototype is 1.71 inches high, 1.75 inches wide, and 2.06 long including the switch and hinge/pin. Or around 6 inches cubed (probably less in reality, considering the switch and hinge were counted in the dimensions).