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Thanks Brendan, I think the favour for the 4 point adjustment was in the way the 3 point affected the x axis when you adjust y whereas the 4 points didn't. I have no intention in re-inventing the wheel, just considering all possibilities since I'm building this from the ground up.
one other thing, with serrurier truss OTA's, are all the truss nodes strictly under compression or tension, or can there be radial forces as well?
I've been looking at the CF tubes, and the common ones are pultruded where the carbon is laid axially, whereas twill weave tubes are multidirectional so have higher axial and radial stiffness.
I got a sample of a pultruded tube and while its very stiff under compression and tension, they're not good if loads are non-axial.
My understanding of truss structures is that all members are always under tension or compression. if that's the case pultruded tubes would do as they're cheaper. I was advised against roll wrapped tubes.
in an exaggerated example, if one were to twist the upper cage by hand like turning a wheel, would the loads on any of the 8 nodes be non-axial?
the real world scenario would be the torque induced by 2kg of camera gear hanging off one side which I presume is very low. haven't calculated that though.
I got a source for 2mm wall 20mm OD twill weave tubes for a decent price but they're about twice the price compared to pultruded.
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