skeleton joints.

msasdfjkl · Post by **msasdfjkl** » Thu Nov 11, 2021 10:00 pm

There is a lot of discussion about the need to improve the movement characteristics of joints in dolls. I have thought about it for some time as I'm sure others have as well. Right now we seem to be stuck with friction joints which are formed from metal to metal connections where the amount of friction which translates to the amount of force used to move a dolls leg/arm/ect is determined by the precision of the person torquing the bolts. Below are the only two solutions I have come up with as a possiblity.

Solution 1:
Use a clutch where the disks are permentatly in contact with one another as determined by springs. The clutch disks itself would be a wear item, however I have the feeling the speed and amount use would be quite low compared to what such a material was designed to do in the first place, to the point where it may not wear at all. https://storefeederimages.blob.core.win ... 43hgfs.jpg . Something like the linked image, but with springs applying pressure to an outside disk. If the right spring force was used it should creat an extermely predictable and constant joint stiffness. There would be a slight change in force while moving a joint due to the difference in static friction and dynamic friction.

Solution 2:
I can't figure out exactly how to do this. The utilization of clock springs or other pulley type system that would allow smooth operation of all joints. Still figuring this one out.
Solution 3:
Slightly more complicated. Use the clutch system as described in solution 1. However the springs are replaced with an inflatable airspring. (Like an air suspension on transport trucks). The pumping mechanism would be placed somewhere like where the knee cap would be imbedded in the TPE. When depressed the clutch disks would engage and stiffen the joint. With another mechanism/button that would release the pressure back into the original resevor disengaging the the clutch plate resulting in loose joints. There would still need to be a spring mechanism to (maybe) so that at rest the clutch plates are naturally disengaged or maybe it doesn't matter. experimentation needed.

That's all I got so far.

ZombieWinter · Post by **ZombieWinter** » Thu Nov 11, 2021 10:06 pm

I believe your 1st idea is best. The other 2 are more complicated and may require higher precision manufacturing (raising costs).

King Solo · Post by **King Solo** » Thu Nov 11, 2021 10:27 pm

I too agree with solution 1 .... as well as some type of locking mechanism located near each major joint. So that way you're able to lock the joint into a specific position or pose before limited free range of motion is applied to the clutch joint.

Kinda like locking the doll into your favorite position and then only allowing a limited range of motion with each joint, while they spring back as you push against them.

ZombieWinter · Post by **ZombieWinter** » Thu Nov 11, 2021 11:20 pm

King Solo wrote:I too agree with solution 1 .... as well as some type of locking mechanism located near each major joint. So that way you're able to lock the joint into a specific position or pose before limited free range of motion is applied to the clutch joint.

Kinda like locking the doll into your favorite position and then only allowing a limited range of motion with each joint, while they spring back as you push against them.

+1

Kaori Kusanagi · Post by **Kaori Kusanagi** » Fri Nov 12, 2021 7:09 pm

Speaking of (overly) complex joint ideas (as well as some simple ones):
viewtopic.php?p=2043678#p2043678

Mbuti Lover · Post by **Mbuti Lover** » Wed Mar 09, 2022 2:57 pm

It wouldn't be too hard to have springs that attempt to pull the doll's joints back to a neutral position, or help maintain a standing pose or sitting pose or legs up in the air pose in missionary or arched butt in doggy. The doll's weight could also help. It would probably be a matter of coming up with the default poses you want the doll to be in, and then cast the doll in positions that would make those possible.

King Solo · Post by **King Solo** » Wed Mar 09, 2022 7:17 pm

jimbob22 wrote:It wouldn't be too hard to have springs that attempt to pull the doll's joints back to a neutral position, or help maintain a standing pose or sitting pose or legs up in the air pose in missionary or arched butt in doggy. The doll's weight could also help. It would probably be a matter of coming up with the default poses you want the doll to be in, and then cast the doll in positions that would make those possible.

The Ruby13 was perfecting this method before they went out of business, due to the founder passing....

It would be nice if other doll manufactures incorporated some of their skeleton designs.... because if they did, we would probably be much further along in skeletal designs and capabilities by now.

Technician · Post by **Technician** » Mon Mar 21, 2022 4:20 am

Pushbutton joints would be perfect, TPE is so resilient I can't imagine fatigue from pushing the button being an issue unless the joint was moved very frequently for a long time. Even then, an occasional TPE repair would be a more than fair trade off for ease of movement and positive locking in place.

https://www.beckerorthopedic.com/Produc ... eries/1800

Also

https://www.rockwestcomposites.com/463090

And

https://adjustajoints.com/product/34-fe ... djustable/

Kaori Kusanagi · Post by **Kaori Kusanagi** » Mon Mar 21, 2022 10:54 am

Technician wrote:Pushbutton joints would be perfect, TPE is so resilient I can't imagine fatigue from pushing the button being an issue unless the joint was moved very frequently for a long time.

As long as there is no sharp line on the interior anywhere around the area being pushed, it's unlikely to fail; the sharp line (like edge of a cylindrical shape, etc) could act as a "cutter" or even just a stress-riser and cause "fracture" lines in the soft material that propagate thru it over time. (or if it is pushed really hard, can cut thru very quickly).

Technician · Post by **Technician** » Mon Mar 21, 2022 1:26 pm

Actually looking at the test weight data this one looks about perfect. The failure weight to pop the mechanism (not break) was more than my whole doll weighs, and at 90 degrees, not a standing position, and the weight would be divided between two.

https://www.rockwestcomposites.com/464090

chachacast · Post by **chachacast** » Wed Jan 04, 2023 1:55 am

I dont think there is a real solution other than use stronger friction joints and learn to weld better and design more functional armatures frames. They could switch to a titanium clevis fork joint and just charge more for the dolls. Constant torque joints will always be needed for proper articulation and posing. When you start adding switches and more moving parts, thats when more can go wrong. There are companies that already make constant friction joints and hinges that have virtually no wear, problem is they are expensive. So for now we will have to settle with metal on metal friction joints.