The Unpluginator - Self-Unplugging Useless Box



About: I'm Dan, hobbyist and maker of things.

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
  • Arduino
  • Motor
  • Capacitors
  • 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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    15 Discussions


    18 days ago

    "No point adding features to a useless box"
    Unless ofcourse these would be totally useless features


    24 days ago

    Funny project!
    How does the mechanism reset itself for the next unpluginating? Do you have to reset it by turning the gears by hand?

    2 replies

    Reply 23 days ago

    Yea, it's pretty much a one shot. I was thinking about putting a spring in, but never got around to it. Maybe someday.
    One of the issues with just putting a spring straight in is that it'll power itself back up again if it plugs in. The motor provides the most return resistance, so I figure sticking a weak spring in and a manually activated clutch to disconnect the drive gear would be a suitable solution.


    Reply 23 days ago

    How about a microswitch placed inside near the plug hole, so that when you pull out the plug, the microswitch trips and signals the arduino to reverse the motor direction to reset the mechanism.


    23 days ago

    Perhaps adding another power chassis socket on top of the first, but pointing to the other side of the box? Ensure that the motor will turn in the opposite direction and you may keep on plugging it......

    1 reply

    Reply 23 days ago

    I like your thinking. I'll get it drawn up this evening.


    24 days ago

    You gave me a laugh, thanks. I see you having a "bunch" of capacitors there.
    Wouldn't it be better to use a cap. in order of Farad?
    I know, these caps are for 2Volts only but anyway...

    1 reply

    Reply 23 days ago

    Yup, but these were the only caps I had handy and they did the job. If it was a commercial product, or something that had to work reliably, it would be properly engineered.


    24 days ago

    If there was an award for the MOST useless box this would place 2nd behind the block of wood. I suppose a block of wood could be used for something other than a box. I retract my first assumption and think you would take place first. Congratulations! Rube Goldberg would be proud! NICE job.


    24 days ago

    I see Dr Doofenshmirtz has been giving lessons again...;)

    Great little project....:)


    24 days ago

    Made my day!


    24 days ago

    Fantastic. You made my day. It serves to perfection what it is meant for: to self unplug. Exactly what I did not need, so I am glad I found this thing. Right on the spot.


    24 days ago

    "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."

    That IS the point! The fewer reasons there are to added features is a tribute to it's uselessness. It's useless on higher conscience. ;)
    Antzy Carmasaic

    24 days ago

    I can relate: "Don't wake me up, let me sleep"


    25 days ago

    Ha! I love it. Taking the useless machine to the next level. :)