Armor Articulation - How To Bend Arms 90+ Degrees?

[NOLAIronMan]

I'm curious if this problem has been solved yet. I'm wondering how to get good arm articulation in an Iron Man arm.

I'm 3D printing a Mk III arm and have properly sized and scaled it to fit my arm dimensions, shown here:

I specifically modified the arm pieces to be as accurate as possible while also giving me a minimum of 90 degrees movement, shown here (it might be hard to see without being zoomed in, but there is enough clearance for 90 degree bending):

(I'm rigidly attaching the elbow to the gold upper forearm piece; this may not be the most screen accurate, but it's an artistic choice I'm making)

However, I'd like to somehow be able to get around 130 degrees of movement. Since the armor is physically hitting itself at 90 degrees, I need to essentially disengage the elbow hinge past 90 degrees and have a new point of rotation, shown here:

Has anyone figured out a method for achieving this?

Here's my thought process: The elbow would have pegs at the normal elbow axis of rotation. Around these pegs would be disc / ring magnets. The bicep loop would be cut in half, and a semi-circle magnet would be placed there:

(The elbow schematic is shown in perspective view, the bicep schematic is shown in side view)

Thus, when the arm is bent less than 90 degrees, the ring magnet is attached to the semi-circle magnet, and the elbow+forearm can rotate freely between 0 and 90 degrees. Once the arm needs to move past 90 degrees, a small tug on the ring magnet (by simply bending your arm with a little force) will separate it from the semi-circle magnet, allowing the elbow+forearm to move freely past 90 degrees.

Thoughts? Is this physically realizable? Are there alternative methods that work and I'm just trying to reinvent the wheel?

Finally, I'd like to note that the 3D print files I'm using are personally modified from Dancin_Fool's Mk III pep files, with his permission.

Thanks!

 

[George]

How about connecting the two pieces with one or more thick,wide elastics used in sewing? They stretch when they need to,but are tucked in on the inside of the arm.

 

[NOLAIronMan]

How about connecting the two pieces with one or more thick,wide elastics used in sewing? They stretch when they need to,but are tucked in on the inside of the arm.

Thanks for the reply. Do you have any examples of the material I could use? All my build experience is with plastics and rigid materials, I wouldn't know where to begin to look for elastics.

Also, how would this preserve the axis of rotation of the elbow?

 

[George]

Separate elastics should be easy to find at clothing stores,tailors etc. They're the same wide type of elastics that you would find in underwear,corsets,belts and so on.If you google it,you should find plenty.
It would seem to me that the mobility/flexibility of elastic is pretty much limitless.Just box it in on the inside of the arms/legs between your 3D plastic printed part and another rigid,flat object.One end of the elastic could be attached to a purse magnet that allows rotation and detachment/disassembly when needing to travel with your costume.

 

[JPH]

Not to be a buzzkill, but when you go to the additional flexion the entire forearm portion is going to get pushed up your wrist/hand. Unless you have an area in the forearm that compresses.

You could use bunjie cables on either side of the elbow as well. Also, are you worried about chaffing or breakdown at that contact points?

1/2 inch aluminum strips that overlap and acordion EDIT: The Acordion pic is not correct dimensions, I just hope it conveys he idea