If not please ask questions. I am trying to paraphrase
so ordinary mortals (non-engineers) can understand it :)


The University of Queensland School of Engineering. Quote:

"Mechanical failure is generally interpreted in terms of change,
some physical or chemical process having produced failure.
However the improper location and guidance of components
also constitutes an important mode of failure often ignored
in mechanical engineering practice."

Any object is said to have six degrees of freedom or movement.
Rotation about the X, Y, and Z axises.
Translation (movement) in the X, Y, Z directions.

In order to hold any object from moving in any way requires only
three  connections. If a fourth, or more, connections are added
additional loads and stresses are introduced that cannot be determined
by simple means. A three legged stool is a classic example.
It is trivial to calculate the loads in the three legs and
the forces these loads apply to the floor. A four legged chair
on the other hand is a much more complicated situation and it
usually requires a finite element analysis computer program
to resolve the individual loads and stresses. The fourth leg
is therefore redundant and in fact considered  undesirable.

Paul Lamar ...No rotor no motor.

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