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Amethyst

## Problem in specifying rotation constrainsts

Actually, i am working on a differential which getting some forces from pinion.

These forces would make an impact on the body to rotate bolt in x-direction.

So, i want to hold the bolt in x-direction of rotation to see the effects of forces.

But as i am doing this i am geeting a warning that these constrainsts wont make any effect.

Ihow should i move forward to analyse the case correctly

1 ACCEPTED SOLUTION

Accepted Solutions

## Re: Problem in specifying rotation constrainsts

Yes a cylindrical csy (created in simulate mode) is a way to do this.  Always attempt a Free Body Diagram.  You seem to be missing the loads/constraints at the output shafts. (R in my image).

Also, the pinion load may be statically redundant if using 2 pinion gears as is typical.  The load may be higher on one pinion gear than another based on manufacturing tolerances and wear.  I would not assume full halving of stress and load is happening due to the 2nd pinion gear.

Also see this for my quiz on mechanizing a differential.

FEA RING GEAR

21 REPLIES 21

## Re: Problem in specifying rotation constrainsts

A basic, fundamental fact of 3D solid elements is that they do not/cannot possess DOF in rotational directions. I will assume you are modeling the areas you wish to apply rotational DOFs with solid elements. If so, Simulate will not allow this type of constraint. Some codes allow for "tricks" through clever interface coding to allow some application of rotational BCs - and these are usually limited, like the "TLAP" in Simulate.

## Re: Problem in specifying rotation constrainsts

What should I do in such case if I want to restrict the rotation?

If it was not possible, then it would have been shown greyed. But at this point, i can apply it but it's not making an effect.

Am I doing something wrong while defining other parameters or its just not possible?

## Re: Problem in specifying rotation constrainsts

Can you use a pin/cylindrical joint constraint? This should allow you to trap the desired direction.

Highlighted

## Re: Problem in specifying rotation constrainsts

The rotation of the pin joint can be allowed or suppressed about the axis of the cylinder surface.

In this case in the x-direction.

But here I want it to restrict rotation in the Y direction to solve the purpose.

## Re: Problem in specifying rotation constrainsts

Yes a cylindrical csy (created in simulate mode) is a way to do this.  Always attempt a Free Body Diagram.  You seem to be missing the loads/constraints at the output shafts. (R in my image).

Also, the pinion load may be statically redundant if using 2 pinion gears as is typical.  The load may be higher on one pinion gear than another based on manufacturing tolerances and wear.  I would not assume full halving of stress and load is happening due to the 2nd pinion gear.

Also see this for my quiz on mechanizing a differential.

FEA RING GEAR

## Re: Problem in specifying rotation constrainsts

Even after using the cylindrical co ordinates. it is showing same Warning box after applying rotational constraints

## Re: Problem in specifying rotation constrainsts

You can't fix the rotation of a surface in that manner.

If you want to fix the rotation and you are not interested of surface deformation, then you might use the pin constraint. Otherwise you should put a point in the centre of the hole, then use a weighted link and then put a ground spring on the point with a very high values of all stiffness.

## Re: Problem in specifying rotation constrainsts

i would try that fraulini

## Re: Problem in specifying rotation constrainsts

When using cylindrical CSY, Theta is the rotation.

Degree of freedom 1 is R (radial), DOF 2 is Theta (rotation about Z) and DOF 3 is Z translation.

Leave those other rotations free. (DOF 4,5,6)