Lego Universal Joints – Constant Velocity to Variable Velocity

Very clever idea.

And with explanation:

“When a universal joint is oriented so that the input and output shafts are at different angles, given a constant input velocity, the output will rotate with a variable velocity.

Within some mechanisms this can be bad, resulting in unwanted vibration. To overcome this, two universal joints can be put together with a specific orientation to form a double Cardan shaft, where one universal joint cancels out the vibration of the other universal joint.

Within other mechanisms, this variation in velocity can be used to our advantage. In this video, four universal joints have been oriented so that their variable velocities do not cancel each other out, but rather, the acceleration and deceleration of the output shaft are amplified.

The input shaft (left) rotates at a constant velocity, whereas the output shaft (right) slows down between the 2 o’clock and 3 o’clock positions, then speeds up between 3 o’clock and 8 o’clock. It repeats this again, going slow between 8 o’clock and 9 o’clock, then speeds up between 9 o’clock and 2 o’clock.

It is also important to note that, on average, both shafts are travelling at the same velocity. They both line up at the 1 o’clock position, and again at the 7 o’clock position.

This mechanism could be used in situations where you need a mechanism to switch between two states, such as turning on/off a switch, or for various mechanisms within a great ball contraption.

Hi-Res photos available.


Very clever…


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Nortebrick 2013March 23rd, 2012
The big day is here.
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