Help needed with resizing a hand

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

Help needed with resizing a hand

Postby Jason M Bryant » Mon Feb 16, 2015 6:12 am

I recently made a Raptor Classic for a recipient. Since he's a fairly tall adult, I made it at 173%.

Because he lost his fingers in an accident and then had surgery on them, his hands are an odd size, and the first gauntlet I made didn't fit. His hand is much thicker than normal, so I thought the Raptor Reloaded would be a much better choice for him. The inside cavity is a better fit for his hand. Also, since the hand has to be so large, the narrower fingers on the RR keep the hand from being so monstrously huge. I've messed around with the RR in Blender 3D and I'm confident I can stretch it up to make it tall enough to fit his hand.

The problem is that the accident and surgeries also changed the shape of his wrist and forearm. They are thicker than normal, with his wrist being 70 mm across and his forearm being 95mm across at the back of the gauntlet. He said that the Raptor Classic gauntlet was a little to tight at the wrist and much too tight at the back. To make this worse, the Raptor Reloaded actually gets thinner at the wrist than the Raptor Classic. The RR gauntlet is even thinner at the wrist.

I put a Raptor Reloaded next to a Raptor Classic in Blender 3D and scaled them until the spaces for the wrists were the same size. To make the RR gauntlet fit my recipient, I would have to scale the whole thing up to 200%! That's enormous!

I thought I could solve the problem by printing a flat version of the gauntlet. Then I realized that takes a bigger print platform, and mine is nowhere near big enough. So that's not going to work.

The best solution is to take a Raptor Reloaded that is scaled to 175% and move just the hinges out to the width of a Raptor Classic at that size. Then do the same thing for the gauntlet, except widen it even more in the back. It has to fit a 90mm forearm, plus the padding. Unfortunately, I think this is beyond my 3D skills. I tried, and I can't figure out how to stretch part of it without messing up another part, like the rail for the tensioner box.

Can anyone help me with this? If someone can widen the wrists on the Raptor Reloaded palm and widen the wrist a little and the back a lot on the gauntlet, that would be a huge help. I'm supposed to deliver the hand in a week, so I only have a week before I need to start printing parts.

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

Re: Help needed with resizing a hand

Postby Jason M Bryant » Mon Feb 16, 2015 1:34 pm

Having done a bit more work on the problem, I think I've got something that works. I scaled the hand and gauntlet in X without changing the Y. Since the hand is thumbless, that doesn't mess up any of the hinges.

It's not quite as good as being able to custom move the wrist hinges. I still feel like there's a little too much room inside the palm. However, it's not too much more. This is probably about as good as this hand needs to be. If it doesn't fit, it will be close enough to tell me exactly what the next one needs.

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Re: Help needed with resizing a hand

Postby hertfordkc » Tue Feb 17, 2015 12:22 am

I had a recipient whose wrist was as wide as his palm, and the palm was relatively short compared to the classic Raptor design. The scaling was 125% for the width of the palm and 115% for the length of the palm. In order to assure clearance for the working of the fingers, their width was 125% but the length was 115%. However, the thumb needed 115% on the width. I printed the thumb's length at 115% also, but 120% or 125% might have worked.
Others have commented on problems when with working with different scaling factors for different axes, but I believe that there is some latitude and it can be a very practical solution to a lot of special needs.

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Re: Help needed with resizing a hand

Postby laird » Tue Feb 17, 2015 2:15 pm

We implemented this in Hand-o-matic a while ago, and it worked great for moderate scaling, but got "odd" for extremes. We're going to be re-enabling it, but until then, from my notes:

- For all parts, scale by the "length" percentage in the direction of the length of the arm and the height of the arm, and the "width" percentage for the width of the arm. Which way those are for a particular piece depends on which way the part is oriented.

For example, the tensioner's "front" points up (it prints on its end), so you'd scale it by the "length" in the Z axis and the Y axis, and the "width" in the X axis.

As Jason pointed out, the thumb needs the scales reversed. This is so that the thumb fits into the socket in the palm, which is at 90 degrees to the other sockets. This means that the thumb socket ends up being an oval, but as long as the scaling factors aren't too different, it'll work.

When the Hand-o-matic has this scaling logic re-enabled, I'll post here so that you can test it.
- Laird Popkin

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