Smokeycub wrote:Again I must be missing something. Mechanically, I can't see how it can change it's speed, even within one revolution.
Yes, that is exactly what happens. The 2x difference happens at 60 degrees, which is a pretty sharp angle and beyond the practical operating range of most joints. It can be worse, imagine turning it to 90 degrees. One end turns freely through a limited angle while the other end is blocked from moving at all.
This is a lot easier to understand by playing with a joint that isn't attached to anything.