This is an example of a Useless Machine. Its only purpose is to unplug its own power supply.
It is largely 3D printed, with the necessary electronics. All drawing and simulation was done on Fusion 360, all programming was done in Arduino.
- 3D Printer
- Power supply + plug
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Step 1: Design and Print
Designed in Fusion 360, I was able to test most of the operation before printing. However, I didn't have any stats on the motor, and 3D printed gears are not exactly frictionless, so had to add another set of gears.
If you have a different motor then adjust the drawings to fit.
For my motor, it came with a wee gear already on it. This was fine, but due to the small tooth size, the connecting gear had to be printed with a very thin outer wall.
Step 2: Assemble and Test Movement
Wire up the motor and plug, assemble the gears, try it out.
If things turn as planned, you'll find something weird happens. Just as the plug gets unplugged, the motor will stop. The tiny amount of flex in the socket carriage will bend back, connecting the plug again. It will then bounce back and forth as it connects and reconnects. For this, we need to ensure there is either enough momentum to keep it turning after the power is cut, or enough energy in the wires to keep the motor turning after the plug is unpluginated.
The simplest way to do this is to use a capacitor. This keeps the power on for just long enough for a clean break.
Another thing to consider is that even with a capacitor, you have to put the plug in quickly, before it moves too far away. This requires a bit more than a capacitor, we need some sort of delay circuit. A few options here, maybe a 555 timer, but I used an Arduino.
Step 3: Electronic Controller
The Arduino code delays the startup of the motor, giving you time to plug the plug in, then ramps up the speed of the motor using PWM to ensure it doesn't rip itself apart.
It would be easy enough to add some lights here, or maybe a beep or two. I went straight for the basics, no point adding extra features to a useless box.
Wire it all up, test it out. If it works, tidy it up.
Step 4: Done!
Put the lid on, and there is your brand new useless box.
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Make it Move