28 Jul 2011, Samuel Hinton

The Most Useless Machine

Now with a use: birthday present denial.

The year before this, I created a thick paper mache wrapper around a present to make it more interesting to unwrap. So in 2011 I decided to do a take on the “Most Useless Machine Ever” - a box that’s sole function is to flip a switch back to its off position when a user flicks it on.

Mechanically, this is simple, the flick just needs to be connected to a DC motor switch, such that either side of the switch changes the voltage across the motor. The motor would turn off with a circuit break attached to the reverse direction that the lever would hit on its return to the default (hidden) position.

To make this interesting for a present box, I wanted it to lock. So I used a circular lever arm, such that as the longer tongue returned back inside the box, rotating anti-clockwise, a second (smaller) lever arm would come forward into a slot in the lid, locking it closed.

But it was too easy to open, so I also wanted it to be locked whilst the tongue flicked out to hit the switch. This was easy to do, I just had the tongue pass through a steel U shape attached to the lid, such that once the lever passed through the U shape the lid could not be opened further than pushed by the tongue.

To have it openable at all, I made sure that the shorter level (which keeps it locked when closed) and the longer lever (the tongue that hits the switch) had an angular gap, such that the smaller lever would disengage before the larger lever would relock the box. And it worked well, so long as you timed it right the box was dead simple to open, and to relock all you had to do is put the lid down and press the switch, as shown in the Youtube video above.

Unfortunately the entire plan fell apart, because the wrapping paper I used trigger the switch and also didn’t allow the lid to open, meaning that overnight the batteries ran out of charge and the box was unable to lock.

We got it open eventually… via disassembly.