Hand scaling

For discussion of Hand-o-matic.
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laird
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Hand scaling

Postby laird » Wed Mar 18, 2015 11:39 am

The scaling logic is an area that we've evolved, and will continue to evolve, based on feedback. The current rule is:

1) The Hand-o-matic scaling rule right now is that the interior of the printed palm is scaled to be the knuckle width of the full hand + the padding. This means that the printed hand is large enough to fit around the full hand, with the logic being that the large size could be compensated for by padding. But if recipients are saying that the hand is too large to wear, that's a "show stopper", IMO.

For example, if the full hand is 70mm across, with a padding of 5mm, scaled the inside of the palm to 75mm, which makes the knuckle width about 90mm, which is much larger than the full hand.

Previously the scaling rules were:

1) The interior of the printed palm was scaled to be the knuckle width of the partial hand + the padding, which was a closer fit, but which could be too small for recipients with narrow partial hands.

For example where this works, if the full hand is 70mm across and the partial hand knuckle width was 50mm, with a padding of 5mm, scaled the inside of the palm to 55mm, which makes the knuckle width about 70mm, which is narrower than the full hand, and would likely cause the wrist to be too narrow as well.

For example of where it didn't work, if the full hand is 70mm across and the partial hand knuckle width was 40mm, with a padding of 5mm, scaled the inside of the palm to 45mm, which makes the knuckle width about 60mm, which is narrower than the full hand, and would likely cause the wrist to be too narrow as well.

2) The knuckle width of the printed palm could be scaled to be the knuckle width of the full hand, so the two hands are the same size. This seems ideal to me, but did result in hands that were too small for recipients with large partial hands.

For example, if the full hand is 70mm across, with a padding of 5mm, scaled interior of the palm to about 55mm, which makes the knuckle width 70mm. So the two hands match (good) but if the partial hand is more than 50mm across, it would be a tight fit.

Are there other approaches that we could try?
- Laird Popkin

PeterBinkley
Posts: 46
Joined: Fri Feb 13, 2015 5:49 pm

Re: Hand scaling

Postby PeterBinkley » Wed Mar 18, 2015 1:52 pm

It's really tough getting a good-fitting device from a rigid model. I'm working toward a flexible bracer (gauntlet) and a wide wrist hinge so that a simple measurement of the residual palm would be enough to make a device. There is a lot of variation in the relative sizes of palms and forearms!
Using the unaffected palm for the interior measurement and adding 5mm of padding makes a huge device, which is definitely a deal-breaker.

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laird
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Re: Hand scaling

Postby laird » Mon Apr 20, 2015 1:22 am

We could certainly use other measurements - wrist width, arm width, affected knuckle width, etc. The current scaling rule, from the designers of the hands, does tend to generate large hands, which will always fit around the affected hand, but will be too large for some people.

Any suggestions for what measurements we should use, and what logic to use to choose between them? That might be a good discussion for a Hand-o-matic Hangout.
- Laird Popkin

ErikDeBruijn
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Joined: Fri Apr 17, 2015 3:15 am

Re: Hand scaling

Postby ErikDeBruijn » Mon Apr 20, 2015 5:47 am

I think that this will work best as soon as the models are not being scaled but actually more parametric. At least for the ones that add value by being parametric.

hmgoes01
Posts: 2
Joined: Thu Nov 12, 2015 8:22 pm

Re: Hand scaling

Postby hmgoes01 » Thu Nov 12, 2015 8:32 pm

I am working on developing a hand for a child as a group project at the University of Louisville. We have been working in Fusion 360 to edit the palm dimensions. Our instructor would like us to contour the user interface surface so that it fits with our 3D model of the child's hand. Do you have any experience with development of contouring the gauntlet/ palm surface? I was under the impression that additional padding could be used where necessary and contouring to the individual's hand is excessive (and a more complicated printing process). Thank you in advance!


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