Welding? More Like “Well, Dang”
Really interesting project!
Sorry, I am not up to speed on all of your iterations or design considerations, but instead of using a centre stiffener, have you considered a higher strength material? For instance Maraging 350 steel has more than twice the ultimate tensile strength as 17-4 stainless. I know a version of this material is used in golf club faces (drivers), so is great testament to it's impact resistance (high toughness).
I just want to say that I really hope you don't quit. I've only been following you for a short time, but watching your process and struggles has been a huge source of encouragement and inspiration for me to work on my own projects. Maybe it's because I'm only an undergrad majoring in engineering and not a real engineer yet, but I think what you're doing is amazing, and I really am rooting for you to see it through.
He is in Quebec province but a partnership with him or at least a consultant external view could potentially help you!
Structurally your cage seems to work more like a net while regular cages are more like shells, which is quite different...
Are the anchors welded on top of the two hoops instead of in between them (which I think would look better) because it makes welding easier?
When looking at the design, my impression is that the anchors seem pretty much only loaded in compression.
Therefore, a few plastics spacers that fills the empty space between the outer and inner hoops might be able to transfer forces compressively from the former to the latter only being constrained in between because of geometry.
plastic is too low rigidity for long structural members, but even a thin walled lego brick can easily support the weight of a person without buckling.
Imagine if there was a thick curved bar of HDPE plastic that runs the whole length between the two top steel tubes and a few other places (avoiding the corners because of the way they bend)
If my explanation was hard to follow I could do a quick fusion 360 sketch.
Resin casting (google guerrilla guide to resin casting) or SLS nylon 11 or 12 SLS printing would probably work for low volume plastic production.