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First off, this isn't ready for testing. It doesn't even have screw holes for the velcro yet. This is just the very first test of the hand. I already see stuff I want to change, like how the thumb is set up. I'd also like some feedback on certain aspects which I'll list at the end of this post. After these thing have been addressed, I'll put STLs up for people to try out.
However, the functionality is already quite good. I took the Raptor and redid a ton of stuff, not leaving a single polygon of the palm. (Although the gauntlet is 100% the Raptor Reloaded gauntlet. Feel free to use your thermoformed RR gauntlets with the Eagle Hand.) Here's a quick overview of the changes from the Raptor reloaded.
Dental Elastic Bands Instead of Elastic Cords
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This is the biggest change, and it has already been tested a little in an RR mod. The elastic bands are much easier to put on and don't require as much force to close the fingers. In addition, the lack of tie-off bars on the palm gives it a much more streamlined, human look. I may even be able to hide some more of those wire routes.
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With the dental bands set up right and some wire routing changes, the fingers bend in a better way now. They always bend at the palm first, then bend at the fingertips only when the palms joints meet resistance. This makes the fingers wrap around objects a little easier.
More Opposed Thumb Position and a Metacarpal Arch
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The thumb has been rotated back a bit. Walking around my home and picking things up with this hand is a joy. Cups just stay in the hand better. The thumb does a much better job of pushing things against the fingers.
The metacarpal arch is the offset of the fingers, so that the ring finger and the pinky are lower than the other fingers. This also aids in grip, since the closed fingers now form a diagonal line that is more perpendicular to the direction of the thumb. On the Raptor Reloaded, these fingers are often too far away from the grabbed object to provide any help.
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I've already written a ton about this. The short version is that it adds some adaptive grip to the hand, so that some fingers will bend more than others, depending on the shape of the thing being grabbed.
Naturally Shaped Fingers
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The thumb look like a thumb. Fingers are round. Fingertips have a wedge shape. This doesn't just look pretty, these things aid slightly in gripping and picking up items.
They're also really pretty.
Several of these features have already received various amounts of testing. I've already incorporated some of the feedback into the studs on the dental bands.
Thumb position: I made it so that the thumb does not lie flat. I did that because having it lean all the way back with this new angle would create an inhuman shape. The resting position is a little strained for a human hand, but it is possible. That's an aesthetic choice.
The downside is that the hand dies not lie as flat on a table as the Raptor Reloaded. Is this going to be an issue? Will it be uncomfortable, or will recipients casually lay their hands on the side and not worry about it? The concern is that they will forget and lay their hands on their tables or desks too roughly, causing damage.
The thumb joint on the palm is a mess: I plan to work on this a lot, hopefully making it have a rounded joint with the palm.
Adult sizes: Will they have trouble grabbing medium sized things? There is a lot of space between the thumb and the fingers. Technically it's about the same as a human hand when the fingers are outstretched. However, when a human hand closes, the palm bends, moving the base of the thumb very close to the pinky, if needed. That doesn't happen with a plastic hand, so this hand doesn't have the same size flexibility. Will hands scaled up for adults be able to palm a basketball, but unable to hold a cup comfortably?
Inner palm space is slightly smaller: It's actually just one corner, where the pinky came down a bit. The rest of the space is slightly longer, making the palm a few millimeters longer than the Raptor Reloaded. Will the corner that I cut off be a problem? This will require some testing and feedback from users.
In addition to these issues, I have a big question for the community. Does this design lose anything that the Raptor hands do well? I don't want to unintentionally sacrifice a design advantage of the other hands. It's important that as we design new hands, we understand what worked in the previous hands.
I could write a whole book on this, but that's enough for now. Take a look and tell me what you think.
The Falcon Hand Team at Seattle Pacific University – dental band system
Skip Meetze – whippletree for adaptive grip
Trouble Sturm and the R&D Hangout regulars – sounding board and idea givers
The Raptor Reloaded designers – The basis for the hand, including the hand shape, the gauntlet and many other details.