The diy skeleton problem

[RevJack]

Why people do not base skeletons around, y'know, human skeleton?
Since the end goal is doll that feels as realistic as possible, skeleton as realistic as possible is something such doll would benefit from.
Granted some aspects would be different, like longer segments for spine or different jaw design (two that come to mind), but overall starting with human skeleton and then altering it as needed would be good design approach.
How common is that?

Problem is that humans have ball-joint joints that constantly repair themselves. They are supported by muscle networks so they don't flop around like a ragdoll.
Doll joints need to be stiff to mimic the muscle tension that keeps us stable, and doll ball-joints can't heal, so when they wear, they get loose.

I am 100% behind a more anthropomorphic skeleton structures inside dolls, hip bones and ribs especially. That part could be done pretty easily within the restrictions of TPE and TPE pours. But the actual joints themselves, I think the gear-joints being developed are the best possibility we have right now.

[rubherkitty]

All we need is a real human type skeleton system all held together with artificial tendons.
Attach various density muscle and fat packs.
Cover this in a tear proof kevlar/poly blend cloth, silicone impregnated and cast inside a doll mold.

I don't think we have the tech nor could most of us afford such a complex assembly of doll.

[blackrave404]

All are fair points.

As for joints, I don't think ball joints are absolutely necessary.
It would be perfect if we could make relatively stiff ball joints that would last for very long time, of course, but I think combined joints (not sure what proper term in english is for that) would be good enough.
Let's take wrist as an example- they have limited movements up&down and sideways (plus combined directions).
You could mimic it close enough with two joints one right after another- one that is responsible with vertical direction and another for horizontal movement. Movement itself would look a bit unnatural, but dolls don't move on their own, so fixed positions is all we care for and those would be realistic enough.

Rotation (like rotating forearm&palm) could also be done by putting one rotatory joint in elbow with another joint attach to it for bending elbow, but I suspect such variety of motion would put significant strain on TPE/silicone. Just stretch your arm in front of you and start rotating your palm to face up and then down, pay attention how much flesh in forearm moves. That would be a concern for TPE/silicone.

And of course all joints should be limited in motion to mimic ranges of human motion.

P.S. And, yes, I'm aware that complexity would inevitably drive up price, but that is not a concern for me in this discussion.

[rubherkitty]

I'm all for making the best, most realistic doll possible.
I never believed the "Cheap Chinese dolls are going to put top shelf silicone doll makers out of business" idea.
There will always be $$ for someone that wants the best.
Datsun and Toyota never killed the exotic car market!

[blackrave404]

There will always be $$ for someone that wants the best.

Heh, true.
Honestly, wouldn't mind looking at RealDoll skeletons.
Interesting how complex those are and how their joints are designed.

[justustoo]

I've been thinking that using a closed centralized hydraulic system to keep uniform tension on the skeleton in much the same way our tendons do, wouldn't be all that hard to implement, and would result in uniform joint tension throughout the skeleton. i. e. ball joints with a central cable run back to an hydraulic actuator (or more than one if necessary).

[squirrel]

have you thought about using threaded rod ?
and matching joining nuts , and nylon locking nuts
these can be drilled and tapped easily enough through their sides to give a bendable joint ,, but with strength

then ,, if you want to put a outer plastic tube over the rod to reduce weight by taking up the space otherwise taken by the TPE material ?

[blackrave404]

I'm not sure hydraulics is the way to go.
Materials will just wear and tear and then liquid will create a mess.
Plus that would require pumps and those are quite loud (unless I misunderstood your proposal)
If we're going all in, then electroactive polymers seems better way to go.
Granted they are currently in r&d stages, but once we have good candidates, we can actually start implementing them in all kinds of things, dolls included. Especially if those can be coupled with self-gluing design to extend lifespan.
But that's approaching synthmuscle territory and that stuff is near future tech, not current year one.

[rubherkitty]

For cable tension joints, why not just use springs? Then you can have specific tension for specific joints.

[justustoo]

For cable tension joints, why not just use springs? Then you can have specific tension for specific joints.

Convenience more than anything else. You could conceal a small pushbutton pump and pressure locking valve pretty easily. I suppose you could do something similar with a spring tensioner, but the pump doesn't necessarily need to be inline with the cable system, just the actuator itself. I'm taking into consideration that sometimes you might want tighter joints (posing) and at others you might want looser joints (shagging). It would be nice to be able to quickly and easily transition from one to the other. Seems a lot of folks on this site have multiple dolls pretty much for that reason.

[SeanSteel]

I think you could dead-end yourself very quickly with hydrolics. I think that the equipment to drive hydralics is heavy and bulky.

If you're looking for squishy compliance, new robotic actuators are designed to be "back-drivable" and are squishy and compliant. I think someone could experiment with tendon drives on an actuator like this...

https://www.robotshop.com/en/my-actuato ... c300a.html

[SeanSteel]

Also, I've seen people on this form get pretty awesome results starting with a halloween skeleton. Has anyone tried using an actual science class skeleton, or do you remember those wood skeletons. What if you made a human skeleton like those wood models

[Iceblazer]

The next evolution of human like mechanics in robotics would likely come from a parody of ball joint movement involving jamming phase transitions graphed to a lightweight framing at specific joints.

[Artbyrobot]

Why people do not base skeletons around, y'know, human skeleton?
Since the end goal is doll that feels as realistic as possible, skeleton as realistic as possible is something such doll would benefit from.
Granted some aspects would be different, like longer segments for spine or different jaw design (two that come to mind), but overall starting with human skeleton and then altering it as needed would be good design approach.
How common is that?

I agree that this is ideal and this is the method I plan to use for a roboticized doll. However, for a static poseable doll, not sure how you'd lock its joints if it is a standard skeleton.