How would you add an opposable thumb to a Raptor style hand?

For discussion of hand designs.
Jason M Bryant
Posts: 198
Joined: Mon Feb 16, 2015 1:59 am

How would you add an opposable thumb to a Raptor style hand?

Postby Jason M Bryant » Sun May 10, 2015 1:41 am

I'm working on a new hand design. It's the same basic style as the Raptor family.

Several people have said they'd love the thumb to be more opposable, like the Flexy Hand. That's proving to be a problem. When I try to figure out where the hinges should go, I get stuff like this.

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As you can see, the proximal phalanx has nowhere to go because it hits the hand. It's also too far to the side. This makes the angle between the thumb and the index finger an acute 'v', when what we want it more of a circle.

The problem is that the Raptor hands put the thumb out to the side, while the Flexy Hand cups the hand, pushing the thumb inward. You can't do that with Raptors because they have to print lying flat on the palm. The Flexy Hand prints in a completely different orientation.

The most likely thing I've thought of in the last few days has been having the thumb hinge be an extra piece that you add on. Francisco Fernandez just posted something along these lines.

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It looks functional, but I'd like a simpler system than that.

Another thing that bothers me is travel system. Is the wiring going to be a problem when the fingers bend 180 degrees and the thumb only bends 90? How does that work on the Flexy Hand?

Jason M Bryant
Posts: 198
Joined: Mon Feb 16, 2015 1:59 am

Re: How would you add an opposable thumb to a Raptor style hand?

Postby Jason M Bryant » Sun May 10, 2015 2:14 pm

There's also this rather ugly option.

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The advantage is that it would definitely work. The disadvantage is that in the resting position, you get a hand position that looks totally unnatural. I'm considering calling this the Eagle Hand, so a bird-like claw isn't entirely inappropriate, but I'm not thrilled about how it would look.

I'm also considering adding a thumb like the flexihand thumb and printing the palm at a 45 degree angle.

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I think this would require getting rid of the proximal phalanx, as the flexihand does. Would we even need a joint between the first two digits? I'm not sure it would add much.

Vladimir
Posts: 8
Joined: Sun May 24, 2015 3:37 pm

Re: How would you add an opposable thumb to a Raptor style hand?

Postby Vladimir » Mon May 25, 2015 11:07 am

Hi Jason

Most regular prosthetics do have an opposable thumb, and I was thinking of adding an opposable thumb as well.

This was recently posted by Octavio Pupo Nogueira https://plus.google.com/118120950409180 ... iBFaWDFi8i

It's for a transradial amputation, but could prove insightful.

I am also concered with the wiring, being that the cable would have a sharp bend which may result in increased wear on that part.


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