How to align two frame axes on Simscape, without connecting the solids

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Hello,
I have a Simscape model of a drone with four propellers attached to four struts. Each propeller is surrounded by a duct, this duct is attached to the strut via 3 pairs of cylindrical and spherical joints evenly spaced at 120 degrees. Whenever I update the diagram I keep having a position violation error and don't know where it comes from. After a closer look at the model I realised that the Z axis of the strut frame and the Z axis of the duct are not aligned, so my question is the following : by looking at my model could someone tell me what I did wrong, and if not, how to align two Z axes of different solid frame without connecting the two solids (namely the strut and the duct).
Thank you,
Best regards
Vincent
Matlab version: Home edition R2018b
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Picture Matlab Help 3.jpg
Duct block
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Strut block

Answers (1)

Steve Miller
Steve Miller on 24 Jun 2021
Hi Vincent,
The joint combination of 3 parallel (Cylindrical - Telescopic) doesn't seem like a useful combination to me. I suspect your model is trying to permit the duct to pivot about its center. You will have a much easier time if you can use a single spherical joint or a single telescoping joint if it must also move up-and-down.
If you really want to model all three attachment points, your joints will need to accommodate for degrees of freedom within the plane of the duct. Your current combination doesn't permit that, which may be leading to the error you are seeing. Pairing a Rectangular Joint with the Telescoping joint on 2 of the 3 connections will allow the mechanism to move (some of those degrees of freedom must be actuated), but it will rotate about the 3rd connection instead of the middle. For small rotations, this may not matter.
--Steve

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