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Hanging A Realdoll Vertically

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DaveC
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Hanging A Realdoll Vertically

Post by DaveC »

I have struggled in the past, when photographing Claire Marie, to get her to stand upright, when supported by her neck bolt. I came to the conclusion that it was because the neck bolt doesn't lie over her centre of gravity, so she swings at an angle to correct this.

George66 has solved the problem by modifying Emma's head. I am too chicken to try this on Claire, so I've had a go at designing a Lifting Bracket to achieve the same thing.

It is simply a vertical rod, rigidly fixd to the neck bolt, with a 4 inch bar at the top, to put the lifting rope over the centre of her head. I've taken a few pictures of its construction, which can be seen by clicking on this thumbnail:-
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The rod material is silver steel (about 50Ton/sq.in). It needs to be high strength because there's a high bending moment from the overhang of the doll's weight. It may not be clear from the pictures, but I've had to put a steel tube around the vertical 3/8in rod. I had to do this, because the rod wasn't strong or stiff enough. A better design would be to do away witht the tube and use a 7/16in diameter rod. The rod has a 5/8in UNF thread each end, of 1in length to attach the top and bottom components. All the remaining components are Mild Steel. I obtained the materials from a model engineering supplier on the internet.

I made the bottom nuts myself, as I'm a tightwad :D but I could have purchased ones instead. The main thing is to really tighten this connection onto the neck bolt.

A 4in offset seems to work. I would not feel comfortable with any more, as this may put too much bending into the neck bolt, which, although high strength, is only a 3/8in UNC thread.

Hope this is of interest. the end result can be seen in Clair's album:-

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mytime
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Post by mytime »

Hi DaveC,

Great idea!
You put quite a moment on the neckbolt.
But it really corrects for the distance the neckbolt is from the "centre" of gravity of the doll.
She really stands straight while hanging free.
Its a neat solution, and looks better than a bolt in the centre of the top of the head.

Mytime & Helen
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dwhite601
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Post by dwhite601 »

Hi DaveC,

Very impressive!. Thanks for sharing.

David

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Cyclops
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Post by Cyclops »

This is what I wanted to see! THANK YOU! THANK YOU!
This is stuff I can go out and buy!


PS, is that a bungie cord tied on at the top?

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midnight
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Post by midnight »

Hi DaveC...thanks for that valuable information; amazing how you figured out that center of gravity and stuff.....you must be an Aerospace Engineer. or something :D :D :wink:

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Post by rentell »

Hey Dave
Interesting solution, thanks for showing us, I shall make one up myself.
You mentioned George 66`s solution to the problem, did I miss the posting on how he achevided his idea??, would you be able to link to the post as I would be very interested to see how he acheived his conversion.

cheers R.
Edit........
Belay that request for info, found it under G66 profile, I shall look into that method as well, if I remember correctly thats the way superbabes are suspended.

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DaveC
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Post by DaveC »

Mytime, I was concerned about the neck bolt. It's a 3/8in UNC giving it a minor diameter of .298in, hence I = 0.000387in^4.
With a mass of 85lbs acting over a 4in arm, the moment is 340in.lbf
Using the bending stress formula My/I the bending stress is 58Ton/sq.in (896MPa).
I'm assuming the bolt is a high strength steel (something like a 12.8 Standard bolt type) which has a yield strength of 65Ton/sq.in (1000Mpa). This means the bolt has a small margin before it bends at a 4in arm.

Cyclops, the thing sticking out of the top isn't a bungee as Claire is bouncy enough already :D
It's actually a piece of nylon cord to which I hook a block and tackle when lifting Claire. The cord just takes the block out of shot when I photograph her. The cordage and blocks are the same type as those used by George66, purchased from a yacht chandlers. They are designed for sail boat rigging being light weight and strong. The cord is only 1/4in diameter.

midnight, I knew my job would come in useful one day :lol: :lol:

Regards,

Dave.

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Post by Everhard »

Outstanding!
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mytime
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Post by mytime »

Hi DaveC,

I come an end, but here hence I = 0.000387in^4. you're calculating a value I can't place.
I have had physics, but I'am not a person that knows all ins and outs of calculating on metal pieces. (I'am not a Jerry).
Maybe that's the reason why I don't get that constant.

Mytime & Helen
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Post by DaveC »

Everhard, thanks for that.

Mytime, I cut out some of my calculation just in case it bored people. But to explain, "I" we call the "second moment of area" and is used in bending calculations. For a circular section, the formula is:-
I = (pi x diameter^4)/64 where pi = 3.14159
so I of the neck bolt = (3.14159x.298^4) /64 = 0.000387in^4

For a rectangular section I = width x depth^3 / 12
so I of bracket top bar = .75 x .75^3 /12 = .0263in^4

The bigger the value of I the smaller the bending stress and the less likely the section will break.

In the formula I mentioned: Stress = My/I
M is the bending moment, y is half the diameter (or half the section height for a rectangular section) and I is the second moment of area.

OK perhaps everyone's fallen asleep so I'll stop there :D

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