# Choose joints

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Hi,

I have to simulate the kinematics of the line trasmission of the primary flight controls and I have many problems in choosing joints.

In this line, motion is given to elements circled in blue in the picture below.

In the picture, green lines define the motion, while nodes red circled are points where I have to insert joints.

Elements need to rotate around the three axis, but rotation around axis off element's plane is limited (8°).

Moreover, in elements with three points, the point in the middle is fixed and only rotation is possible. I tried to insert in those points revolute joints and in other points I tried ball joints but I didn't know how to limitate rotation up to 8° so I tried many joints but with poor results.

Consequently, I would like to ask you which joints could be good in the elements in the picture.

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Hi Laura - Defining revolute in all places will lead to model being over-constrained. That means, overall there are more constraints than the no. of degree of freedom. In reality, are all of these pin joints ? Or are there ball joints too. ? You may chose to work on a combinations of revolute and cylindrical/ball joints to avoid over constraining.

Alternatively, you can define joints with compliance. (Turn on "Allow Compliance" check box while adding the joint). Then you'll get the option to toggle the joint from non-compliant to compliant. So then it is not really an idealized joint but a bushing with stiffness and damping property. Provide high stiffness values (1e6 or high) in all directions except Rotational Z. (leave it to zero).

Provide some minimal damping (0.1% of stiffness is a good starting value).

Regarding the out of plane rotation of 8 deg, you may want to model based on what exactly causes that rotation or what exactly limits the rotation to 8 deg. Is there some kind of a gap/play somewhere?). To begin with, you might want to ignore that out of plane rotation.

regards

praful

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