Doll hand that grips

[doll-o-grapher]

The threaded rods I linked above, put another of the electrical eye shaped terminals on each knuckle (on the side away from the hand), run a cable from the crimped down part along the underside of the finger in to the wrist, with a light duty spring like that used on a Carburetor as 'throttle return' spring.

If you want to go full robotic, swap out the spring for a linear servo motor.

Add pressure sensors on the cables, and a PID loop based control using an F4 flight controller or Raspberry Pi, and you can control the grip from gentle-with-the-eggs to OMG-She-wont-let-go!

My point with the post above was - why re-invent the hardware when it already exists. The hardware is where we all get hung up, but with off the shelf parts we can whack the hardware together and concentrate on the control mechanisim software.

[Technician]

Heim joints are common knowledge, and would be a good choice for some things on a doll, like a ball and socket spine for instance so I agree they could be useful in a project doll. The concept of the hand is: simple, durable, cost effective - heim joints are simple and very durable but not cost effective since it would take 3 just to do a single finger. Also a doll isn't exactly a piece of military hardware, the hand has to be strong enough to repeatedly hold objects for photography and such, not fire a machine gun. It only needs a grip strength of 5-ish pounds.

What I'm trying to prototype is cheap, simple, self contained and far more durable than finger wires. On that note, I found some different spring material in .25" and ordered the other day. It's more along the lines of the snap bracelets that kids play with. It's rated just over half of a pound but thin enough to install as many as four layers. Each finger should have about 1.5lbs of grip strength to be useable ...... I think ..... this is my first go at prototyping a robot sex doll hand so trial and error is going to have to tell the story.
In the end I'd like to try to fabricate an entire hand that splays the fingers when opened, and has a grip down to within maybe 1/2" of a fist (not expecting any hand to hand combat in the chamber where my dolls sleep so no fists) then move on to actuation or a ratcheting mechanism.
Lately I've been experimenting with a very small vacuum pump that's really quiet, runs on 4.5VDC, and drops just shy of 20 in hg, so I'm putting some thought into an air muscle type creation to use vacuum or possibly a couple of very small pneumatic cylinders in parallel.
I'll post my findings when the new springs arrive and I may may even get some aluminum tubing involved so it's all terminator looking.

[doll-o-grapher]

heim joints are simple and very durable but not cost effective since it would take 3 just to do a single finger.

The ones I linked from the RC Model supplies, I thought were very cost effective.
Might be that I'm used to seeing larger ones be a lot more expensive, especially the sizes used on race cars.

We're happy to add $80 to $120 (depending on your currency) for standing feet or shrugging shoulders, an option of around the same value for 'advanced gripping hands' compared to the normal wired type fingers would be pretty good value IMHO.

Splayed fingers - there'd be enough sideways movement in some versions of the Heim joints to do that with ones at the base of the fingers, and I'd agree on it being a desirable feature - hands is one of the two areas that break the illusion when looking at some of the better photography out there, as that lack of splaying leads to the fingers not sitting in natural positions.

And half a fist will be more then enough - to look good cupping breasts or resting on thighs, or posed with a cup or utensils or pen or mouse,..

Terminator look? You'll need a head that looks like Summer Glau

Another thought crossing the mind - what are most manufacturers using for the end of the skeleton structure at the wrist?
The winkle lines across the wrist would make an easy way to hide a cut and joint, if one wanted to carefully turn the TPE/Silicon of a hand in to a glove to ease over home made hand skeletons, so long as they could be easily attached to the existing structure.

I'd love a couple of joints in the spine too - one at the base of the neck, another under the ribs, and a third at the hip frame, allowing closer simulation of normal spinal curvature.

[pursuitofperfection]

@dm1234

So, I think I understand what type of action you are looking for. Slowed and controlled, like back in the day when tape decks would open slowly by some sort of mechanism. The only thing that comes to mind nowadays are "oh sh*t" handles on cars. They have that automatic foldback action when not in use. Maybe go rip one out of a car just to see how it works. I'm sure there is a torsion spring and a small gear mechanism that has a lot of drag on it inside. The drag of the gear mechanism slows the return rate of the torsion spring.

[Technician]

I've been thinking much more seriously about getting a 3D printer in 2023, that would open some new doors for fabrication of finger bones and much more. Shooting nylon is far more common than when I researched it a couple of years ago, and nylon is tough stuff so that could make a great material that's strong and machinable after printing. Also there's TPU and TPE filaments which could lead to printing flexible joints and tiny airbags for actuation.
Nylon tubing is available in 1/8" OD, and finger motion would really only require 1-2 PSI so thin nylon tubing and tiny TPE airbags could really lead to something interesting.
Valving is a problem, I've been looking for efficient, cheap(need many), low voltage solenoid valves and haven't really found anything that felt right, there are, however very small 8mm and 6mm stepper motors that run in the 3-6V range so with a 3D printer shooting nylon it wouldn't be insane to try printing cheap nylon valve bodies. Some of those tiny steppers are interesting in that they terminate to a tiny leadscrew complete with a cradle to support the ends of the screw.
Tiny servos are inexpensive as well and one PCA9685 board can drive 16 steppers from I2C commands, and they're addressable so they can be sort of daisy chained to run up to 992 servos, so that's definitely expandable beyond anything doll robotics considering humans have about 700 muscles.

[MannequinFan]

Wow how time flies, it's been a while since I posted in this thread.
If anyone's interested, I've made many improvements to my replacement hand skeleton design since then.
Parts are now available here from Sculpteo printed in HP's Multi Jet Fusion (MJF) nylon. MJF is much stronger than FDM printing (no layer weakness).
The two end finger joints are now hinged instead of wire, and finger bones are round instead of square profile.

Click on image below for more info...

[-Ragnar66-]

Wow how time flies, it's been a while since I posted in this thread.
If anyone's interested, I've made many improvements to my replacement hand skeleton design since then.
Parts are now available here from Sculpteo printed in HP's Multi Jet Fusion (MJF) nylon. MJF is much stronger than FDM printing (no layer weakness).
The two end finger joints are now hinged instead of wire, and finger bones are round instead of square profile.

Click on image below for more info...

Thanks, bookmarked!