Most Useless Machine

Owen

The box features a switch and a hinged lid. When someone presses the switch an arm inside lifts the lid, switches the switch back in the opposite direction and then closes again. Useless, but strangely compelling.

After seeing the original most useless machine ever I couldn’t resist making one myself, not for myself though, this one was a present. As the site hosting the original is horrible, I used the nice clear instructions provided by Make Projects.

I spent some time looking for a suitable box to house the machine’s useless innards, but finding one the right sort of size without any ugly decoration proved tricky, so I opted to make the box myself.

Useless machine

The arm popping out to turn itself off

The way the box works is down to the arrangement of the two switches. The switch on the top of the box is wired so that in one position the motor will rotate to push the arm out of the box, and then when switched in the other position the polarity to the motor is reversed and the arm rotates back inside.

The clever bit is that the side of the switch which causes it to rotate back inside is wired in series with a microswitch which disconnects the power to the motor. The arm that pops out has a cam cut into the end nearest the motor which activates the microswitch once it has fully retracted, turning the machine off.

The machine consists of the following components:

  • A box
  • A DPST switch
  • A microswitch
  • A geared motor (I converted servo)
  • A battery box
  • Some kind of arm
  • Hinges
  • A battery box and batteries
  • Thermoplastic
  • Metal hooks
  • Rubber bands

Useless machine

The wooden arm and elastic band keeping the lid tight

As suggested in the Make article I drew around the components I had and then arranged them so that they would fit within the dimensions of the wood that I bought. This gave me an idea of how everything would be arranged in the box.

I made the wooden box and rotating arm from a single piece of pine from B & Q cut into sections which became the various sides and lid. I glued the  sides together and then secured with some small nails for extra stability.

Useless machine

The thermoplastic servo mount and other gubbins

To move the arm I took the control board out of a servo and connected wires directly to the motor. This gave me nice slow, powerful movement that could be controlled by simply applying power, no PWM control necessary.

The servo and arm wouldn’t quite fit in the box while horizontal so I had to devise a way to fix it in place at an angle. As time was tight I decided to make a mount for the ┬áservo and microswitch using thermoplastic. This softens enough to be moulded by hand when heated above 60C and then when cool again becomes rigid.

Useless machine

The cam which operates the microswitch

After I’d installed everything into the box and got it working I found that the lids would often get stuck in a raised position due to some stiffness in the small hinges. To solve this problem I screwed some metal hooks into both the lids and two places on the bottom, then I linked the eyelets with some small rubber bands. These pulled the lids down enough to let them spring back into place when the arm retracted into the box.


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