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 hadn't looked at the Maraging 350 in particular, but -- as far as I understand my problems -- it isn't really the tensile strength that was the limiting factor in the design. The frame wasn't breaking, so it wasn't reaching that ultimate strength. In fact, it wasn't even yielding / plastically deforming.
So my problem was still in the elastic range, which is the realm of Young's modulus. 17-4 has a pretty high modulus of 28.5 x 10^6 psi, Maraging 350 is apparently a comparable 29 x 10^6 psi. Just going off the wiki list (https://en.wikipedia.org/wiki/Young%27s_modulus#Approximate_values), my only somewhat reasonable way to step up seems to be tungsten carbide, but nothing in engineering is free -- so it's tensile strength is quite low. As far as I can see 17-4 is my best solution for now. Maybe eventually if I can design a full mask around the concept, things could be different, but for now, the vertical bar seems to be the right way to go.
From my limited knowledge steel alloys pretty much all have the same stiffness, so high strength steel is only pertinent for applications where you expect the steel will flex substantially because they can handle that better (also applications that need hardness)
However for a lot of structures you want to focus on reducing flex in the first place
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.
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.
- they would hold the net away from the mask and prevent chafing
- I could't come up with a bend radius tight enough to get them between the two hoops (the gap's only ~.25")
New design will have the anchor at least partially on the inside -- should help the load path.
I played around with a few similar ideas (I'll detail them more in the next update) but ended up not liking where the rope would end up and also wanting to just go with materials and methods that I know will work. There's always a v2 and even if that's a better solution, I think it will take a little more time to fine tune
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).
Thanks!
I hadn't looked at the Maraging 350 in particular, but -- as far as I understand my problems -- it isn't really the tensile strength that was the limiting factor in the design. The frame wasn't breaking, so it wasn't reaching that ultimate strength. In fact, it wasn't even yielding / plastically deforming.
So my problem was still in the elastic range, which is the realm of Young's modulus. 17-4 has a pretty high modulus of 28.5 x 10^6 psi, Maraging 350 is apparently a comparable 29 x 10^6 psi. Just going off the wiki list (https://en.wikipedia.org/wiki/Young%27s_modulus#Approximate_values), my only somewhat reasonable way to step up seems to be tungsten carbide, but nothing in engineering is free -- so it's tensile strength is quite low. As far as I can see 17-4 is my best solution for now. Maybe eventually if I can design a full mask around the concept, things could be different, but for now, the vertical bar seems to be the right way to go.
From my limited knowledge steel alloys pretty much all have the same stiffness, so high strength steel is only pertinent for applications where you expect the steel will flex substantially because they can handle that better (also applications that need hardness)
However for a lot of structures you want to focus on reducing flex in the first place
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.
Really appreciate it Nate! No plans to quit just yet. Very glad to hear that it's helping your projects along!
https://www.facebook.com/profile.php?id=100054474009333&mibextid=ZbWKwL
He is in Quebec province but a partnership with him or at least a consultant external view could potentially help you!
Thank you Yannick -- looks very promising! I'll reach out.
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.
There were on top because of
- ease of welding / spot weldability
- they would hold the net away from the mask and prevent chafing
- I could't come up with a bend radius tight enough to get them between the two hoops (the gap's only ~.25")
New design will have the anchor at least partially on the inside -- should help the load path.
I played around with a few similar ideas (I'll detail them more in the next update) but ended up not liking where the rope would end up and also wanting to just go with materials and methods that I know will work. There's always a v2 and even if that's a better solution, I think it will take a little more time to fine tune