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Bosourire1-Visitor
1-Visitor
March 23, 2018
Question

Half Angle Constraint for CV Ball Joint Mechanism

  • March 23, 2018
  • 3 replies
  • 2199 views

Hello,

 

I'm building a Ball type CV Joint CAD model for a mechanism study and I'm having difficulties constraining the ball cage which is usually half the angle of the joint itself.  The outer race is constrained as default and the inner race (and shaft) are constrained with two constraints; ball for pivoting and general for clocking the rotation.

 

The problem is with the ball cage which needs to be half the angle of the inner race.  I created a user defined analysis of the angle between the outer and inner races which I called "CV_Angle".  Then I created an axis between the planes of those two races and use that axis to create a relative half-angle plane with the offset angle defined as "CV_Angle/2".  Finally, I constrain the cage to that plane and clock it with the inner race and attach the balls to the cage.

 

The problem is that the user defined value of CV_Angle doesn't appear to be updating in a dynamic fashion and the cage and ball do not follow the half angle of the inner race.  Looking for a solution...  Thanks!

3 replies

T
TomD.inPDX17-Peridot
17-Peridot
March 23, 2018

If you are using angles in your mechanism constraints, you can limit them there.

 

 

B
Bosourire1-VisitorAuthor
1-Visitor
March 23, 2018

 TomD,

 

Thank you for your  reply.   You are right, I might be able to create a half angle servo motor that actuates the cage but I think that it would much simpler if I could just get the analysis value to regenerate dynamically. 

T
TomD.inPDX17-Peridot
17-Peridot
March 23, 2018

That's not what I was thinking.

 

I've done conventional U-joints where I could control the max angle between elements.

This kept the assembly from locking up while dragging the tail shaft.

The only difference in your application is that the "U-Joint" [the balls in the yoke] is that the half-shaft can move linearly inside the hub.  I would add this on top of a conventional U-joint constraint set.

This sets up how the assembly sequence should be constrained as well.

 

I will ad this disclaimer... most of my mechanism efforts entail some level of "driven" results if I need the motion analysis to run but not all links are constrained logically in the assembly.  For instance, I won't make a surface tangent to a screw thread when I can mimic the thread parameters with a generic gear ratio.  I've run multiple servo motors to match the desired results.  But that doesn't mean my assembly constraints are lacking... it just means the CPU didn't need to be taxed so much.  But like you, I definitely want the dragging function to be functional up to allowable physical limits.  I also do not use collision detection (if I even have that?).  Have a look at the recent mechanism thread which includes the model of a double U-joint in Creo 2 I uploaded.

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