Tuesday, 30 April 2013

LEGO Technic useless machine

In popular mechanics, a "useless machine" is one that does nothing beyond turning itself off again. When made in LEGO, you will often find them powered by a motor, by gravity, or by some other means. When I saw the new wind up motor in the LEGO Technic sets 42033 and 42034, I knew it could be used to power a "useless machine".

The only disadvantage of using a wind up motor, is that it runs very fast. It easily reaches a high speed, as long as the friction is low. To overcome this problem, I put a clockwork escapement mechanism into the machine, to limit the speed of the motor when the device is running. Here is the result:

The black 12t bevel gear on the lower front of the machine winds up the motor. Turn it clockwise to wind up the motor. While winding it up, there is a ratchet gear which slips, allowing the rest of the machine to be stationary. The grey 24t gear in the centre below slips upwards while winding up the motor:

When the motor is allowed to run, though, the 24t gear does not slip, but the movement is transferred to the grey 7L axle on the right below, which turns the 3L liftarm, and lifts the yellow pusher mechanism.

What initiates the movement in the first place, is the red beam switcher, which pushes the black crossblock to the right downwards. This lifts the small grey wheel up, releasing the 16t grey gear and starting the yellow pusher action:

Once this axle starts turning, the dark grey crossblock and the dark grey 3L beam attached to it prevents the wheel from locking with the grey 16t gear again, until one full round of rotation has been achieved:

After one rotation, the grey hub slips down again, locking the 16t gear so that the yellow pusher is in the lower position:

Here, the yellow pusher is in the lower position:

I chose the double pin wheel clock escapement type, which is simple and easy to understand:

The pendulum is hinged at the tan pin in the centre of the dark grey 24t gear. The black pins move towards the upper part of the pendulum from each side, in an alternating way. As on pin hits the pendulum, it has to swing to one side before allowing the pin to pass. Once it has passed, the pin from the other side hits the pendulum, forcing it to swing the other way. This keeps the motor running at a slow pace when the mechanism is engaged.

The dark grey 24t gear is used solely for the purpose of achieving a half stud offset in two directions, by using the pin hole connectors.


  1. Hi, i am building your useless machine but i cant really see everything on the video or on the pictures, could you please do a step by step turorial.

  2. Hello, I am trying to build your machine but one of the things stumping me is how the whole stopping mechanism for the pullback motor works. Can you make some other thing dedicated to showing a tutorial on the stopping mechanism? I would appreciate it.