The U-joint puzzle

[Lorne Heslop <HESLOPL@domain.elided>]

Joel and others in the U-joint puzzle:

I agree with the input from Bill Thiebert regarding U-joint phasing.  In a
2-joint shaft, the input and output joints should be equal and opposite. 
That is the yoke on the end of the transmission and the yoke on the
differential should be parallel.  If the output shaft of the transmission and
the input shaft to the differential are parallel, this ensures that the
oscillations that exist in the centre shaft are cancelled in the final joint.  I
believe the theory also extends to situations where the centre shaft is X
degrees relative to the transmission and the differential is 2X degrees.

"Situations involving 3 or more U joints become more complicated."  This
was the concluding comment by my engineering professor in the lecture
of U joints.  We went on to a new subject in the next lecture.  Shortly
after graduation, I was faced with a production problem in which drive
lines were exploding in the field because of joint phasing.  In this 3-joint
case, the output joint was 90 degrees to the input joint and the centre
joint was essentially at 0 degrees except for cornering. (pull type farm
machinery)  The essential field fix was to rotate the output joint until it
was parallel/ equal and opposite to the input joint.

Another good way to analyse the situation is to pretend you are situated
in the plane of rotation of the 1st yoke.  This plane of rotation is a circle. 
The 2nd yoke will describe an ellipse on the plane of rotation of the 1st
yoke.  To do this the speed of the 2nd yoke must oscillate.  to balance the
oscillations, the next yoke assembly must transform the ellipse back into
a circle.

I hope that a little bit of the above is clear.

Lorne Heslop
Almonte, Ontario