Universal Joints

    A Universal Joint, or a U-Joint, is among the most common obscure things you possess many of. At least two for each car you own, plus you probably have one in a ratchet set. Why are they useful? When a rod is rotating, it needs to be completely straight, or it will look wobbly. Plus, the input and output must be in line with each other. But if that were the case, all vehicles would have to be so low to the ground that the engine and transmission would both take damage. Thus, we needed a way to allow a rod to rotate at angles, dropping it down simply and easily.
    We already knew how to make a simple joint, one with the parameter only along one plane. This is like your knee. It only bends one way. But rotation requires that this joint also rotate. So what if we combined two parameters along perpendicular planes, planes that rotated? Concept, check. Having a second, perpendicular plane creates a three-dimensional parametric system, so that the altered line does not need remain on the plane. Instead, the planes can rotate all they want, without disturbing the alteration. As this rotates, the individual components of the 3D vector change, going from positive max to zero to negative max.
    I have only found one problem with U-Joints so far, and that is their angular limit. Somewhere between 30 and 60 degrees is their limit, and at 90 you can get what I call "Wobbly Lock". Wobbly lock is where the components 'Lock', turning the 'Wobbly' into a pivot. This makes a poor excuse for a wrench. So keep that in mind next time you change your spark plugs. This can get annoying.