Saturday, 23 February 2013

Geneva drive in Lego Technic

The Geneva drive is a mechanical device that transform a smooth rotation into an intermittent rotary motion. Traditionally, this has had applications within watch making.

The Lego mechanism showcased here transfers one rotation of the drive axle into 1/4 rotation of the output axle. Here are the basic movements explained.

The driving axle (to the right) locks the output axle, due to the black half circle shape.

Sunday, 17 February 2013

Helicopter rotor with cyclic control

In 2012, LEGO released the 9396 Helicopter model. While this is a good set, with realistic looking helicopter blades, the blade operation is still far from realistic.

The model includes collective pitch adjustment for the rotor blades. The word collective in this case refers to the fact that the pitch of all the blades change at the same time, collectively. This is all well, however, not really anything new, since this feature was also included in the 852 Helicopter model from 1977!

The key to the success of the helicopter is the cyclic rotor pitch adjustment, usually operated through the pilot's stick. This involves having a swashplate below the rotor, to which there are rods connected to the rotor blades. The rods control the pitch of the blades. As the swashplate is tilted, the pitch of the rotor blades change cyclically through the rotation. This animated GIF explains how the a tilted swash plate affects the cyclic blade pitch:

Animation made by Richard Wheeler (Zephyris) for use in Wikipedia, and uploaded using the GNU Free Documentation License

In the animation, the disc below the rotor is the swashplate.