Thank you both for the helpful replies — I really appreciate you taking the time.
To give a bit more context, the model is a 1.4 m rotating arm with a linear motion axis mounted to it. The left “fixed” end in the model will actually be connected to a motor-driven rotating hub; the other end is hanging free in space but the tip needs to have minimal displacement under the load riding on the linear axis as it moves back and forth along the arm. It’s a bit like a miniature tower crane.
I’m new to FEA. I initially modeled the “cable” as a solid steel element, assuming it would always remain in tension under load and that this wouldn’t matter — which, as I’m now learning, isn’t a safe assumption. I haven’t used truss elements before, but I’ve done a tiny bit of reading on them since your replies.
I do have a question about implementation. I’m not sure how best to get the required 1D geometry out of Fusion 360 and into PrePoMax alongside the 3D geometry. As far as I can tell, STEP export from Fusion doesn’t include sketch entities. One idea would be to extrude the sketch line into a very thin surface and then select only the edge for meshing, but I’m not sure if that’s good practice. Importing a 3D STEP file and a separate 2D DXF also feels like it could easily lead to alignment issues. Is there a tutorial video that might help me with first time usage?
I also have a question about partitioning geometry. Is this something that’s ideally done at the CAD stage (by splitting bodies or surfaces before export), or is there a straightforward way to do it inside PrePoMax if I didn’t plan far enough ahead in CAD?
Finally, to clarify one point: I’m not actually trying to model the cable sliding over the top of the post. In retrospect, tying the cable at the top of the vertical post would clearly give minimal beam deflection. That was a mistake on my part — I was only thinking about compression in the post and didn’t think about how it might lean under un-equal forces.
@fatmac — would you consider sharing a very simple spar-and-truss example that I could study, just to understand the setup and workflow?
Those research papers are a bit too advanced for me I think. However I’ll have a good read of the forum link about tension_only cables.
Thanks again for the guidance.
Oh yes, simply adding mesh refinement to my existing round top model did indeed get sensible results! However this is also a great opportunity to learn about truss’ and the other things mentioned.
Edit: One more question — possibly a very obvious one. Is there a way to hide or show geometry while a constraint (or similar) dialog is open? At the moment, if the surface I want to select is obscured by another part, I have to select a random surface, exit the dialog, hide the obstructing object, reopen the dialog, make the correct selection, then exit again and restore visibility. That feels very inefficient, so I suspect I’m missing a simpler workflow.
