You also wrote some interesting things about mounting payloads. But here I wonder whether the system you envision would prove applicable to all the different kinds of payload that the SX45 has been fitted to carry? The last page of the "Mobile Elite" brochure has a few schematics of the possibilities: missile system carrier, bridgelayer, system cabin…..a ladder frame chassis that is torsionally stiff enough for the forces that act on it to not twist it.
AbsolutelyNo such thing as a "100% Torsional Stiffness" chassis. Doesn't exist, never will. All structures will flex. Some can flex significantly before failure, others barely distort before failure, but they all do flex.
If I may rephrase so you don't contradict your previous affirmation: torsionally stiff enough so that the twist caused by the forces that act on it is not great enough to damage the payload?What can exist, and possibly does, is a ladder frame chassis that is torsionally stiff enough for the forces that act on it to not twist it.
My issue with the semi-rigid mount is that as the frame twists it compresses the springs which in turn pull on one or other corner of the payload. It's not torsion free, it just reduces the stiffening effect the payload has on the chassis (see your point below), and reduces the twist the chassis exerts on the payload.If there is such a thing, I think that they are not necessary with a 'normal' chassis, that simply resting on the top rail with anti-friction methods in place as well as methods that allow the frame rail and the part resting on it to move independently while still securing the payload is all that is needed. To me that is several straps or bolts with compression springs not fully compressed per frame rail.
AgreedI think it unwise to try to increase the torsional stiffness of the chassis with the payload. Trying to do so will create a large stress riser at the point of transition from your efforts to the OE's frame.