Originally Posted by niznai

That's not how ECS driveshafts work. In reality they're nothing else but CV driveshafts (CV=constant velocity) but such is the generation Y world, everything has to have some incoprehensible acronym today to attract their attention to repackaged old technology. Xray is good at this and optimising too.

The problem with the single universal joints is that when the shaft goes through a rotation, the axle (the other shaft if you will) does not rotate around the same arc (because the cross in the joint is at 90 degrees - CROSS joint, get it?) therefore putting a small stress on the joint. As the rotation continues, the axle "catches up" and compensates for this small difference, so after a complete rotation both shafts have done 360 degrees, but rotational speed is different on sections of this complete revolution. The double jointed shafts compensate for this because the second joint (or uni if you will) returns the point where torque is applied to the driven shaft at 0 degrees to the input shaft.

Imagine you have a piece of string with a weight at the end and you spin it in the air, standing in front of a wall with a source of light behind you. The shadow of your weight on the wall will be a circle. If you move sideways, the shadow changes into some sort of ellipse. This elipse does not have the same circumference as the circle that was there before, so the shadow of your weight must travel at a different speed to the weight at the end of your rope to cover a different length trajectory. The truth is that the shadow speeds up and slows down and you will be able to see this in the shadow. In total, the shadow takes the same time to do a full lap of its trajectory, just as your weight does, but the shadow doesn't go at constant speed. That's what happens with a uni joint, where your weight is one arm of the cross joint and the shadow is the other arm (which in corners does no longer go on a circular trajectory as viewed from the input shaft). The angular speed of the two is the same, but equal angles do not divide an elipse in equal lengths on the circumference as they do with a circle. That's where the problem comes from. Using two cross joints overcomes this problem as the difference introduced by the first joint is cancelled by the second.

Hopefully this makes some sense.

There is a website where you can just plug in these questions:

"howstuffworks"

Most companies offer ECS driveshafts these days.

Try it.