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The first is a white Raptor Classic. It uses rubber bands for the elastic. I just took regular rubber bands, cut them once each to make long strings, and wired the hand up.
The second hand is a red Raptor Reloaded. It uses the kind of elastic cord that is recommended by eNable.
The funny thing is, the rubber bands on the white hand work much better than the elastic cord. I have it strung up tightly enough so that the fingers pop fully upright, yet it is easy to close the fingers all the way. The hand with the elastic cord barely gets the finger fully upright, but takes a lot of force to get the fingers near fully closed. I can't really get them completely closed.
I did a little testing and found that rubber bands can stretch to about 500% of their original length, while the nice elastic cord only stretches to 150%. So obviously the elastic cord is hitting its limit. This is more of a problem on the smaller hands, which have less elastic to stretch. That might also help explain why I had an elastic cord break before any of the rubber bands broke. The rubber bands still have stretch to spare even when the fingers are fully closed, so they're not feeling the strain.
That led to me creating the third hand, a blue Raptor Reloaded with fingers based on the Falcon hand. It has studs on the fingers and palm that hold little rubber bands, the kind you get from your dentist to put on braces.
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I'd like to thank Adam Arabian and the Falcon team not only for the idea and the design work leading to this, but also for the support and information that he shared on the forum.
First off, I got the wrong dental elastic bands. Adam instructed me to get the medium strength, 6.5oz bands, but I got the medium 3.5 bands. Also, my studs are bigger than his, which stretches the bands more. Several bands have broken, but obviously that's because they're not the right bands. So I can't really talk about the durability of the bands just yet. I am trying to order some stronger, slightly longer bands. I'll post some more once I can test the hand with the proper bands.
At this point, I do have a few thoughts on the design. It seems to work pretty well. The dental elastic hand does not close as easily as the rubber band hand, but it does close easier than the elastic cord hand. I'll have to reevaluate that after I get stronger bands, but so far it looks good. Hopefully someone with a strength testing rig can make one and compare the force needed to close the different hands.
One interesting thing is that the force is distributed differently. At the very beginning of the motion, the dental elastic hands require a little more force. However, that force doesn't seem to increase much as I continue pushing the fingers closed. On the hand with elastic cord, it starts off very easy and linearly ramps up as you get closer to closing the fingers.
This might be improved by experimenting with different lengths of elastic bands. The ones I got were 3/16, which I believe means they have a diameter of 3/16 of an inch. There are many other sizes, and I'm trying to get 1/4 now. If they are longer, then they won't be stretched so much at their starting positions. That should make it easier to open the fingers for the full range of motion.
It's also worth noting that we'll probably need different sizes for different scales of hands. Here's a picture of a 175% percent finger that I made, which would fit an adult hand. As you can imagine, getting the rubber band on that was extremely difficult, and the band broke within a minute. If some people would volunteer to test this, hopefully we can try a few different sizes of dental bands on a few different scales of hands.
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Here's the big thing. These are *much* easier to put on. The goal of the Falcon Hand team was to make something that can be put on with one hand. It's not easy, but I managed to do that. That means that you can give your recipient a little bag of rubber bands, and they can fix any broken bands themselves.
I'm probably going to make this hand my new test hand. It is much easier to put on the dental bands, and I don't have to waste the elastic wire every time I restring a hand to try out a new part.
I'm pretty happy with the design of the fingers, although further testing will show if any tweaks are needed. The palm is a complete hack. I just stuck on the studs where they needed to be. If this were an actual attempt at making a hand with this system, the Raptor design would need a significant overhaul to accommodate the Falcon Hand elements. Maybe we'd call it the Raptor-F class.
However, it's good enough for testing the concept. If anyone would like to take a look, the files are here. I've got palms with and without support, for both left and right hands. Any parts that are not here (wrist pins, tensioner box, etc) are the same as the standard Raptor Reloaded, so you can just use those files.
https://www.dropbox.com/sh/eq6rdl6kffjt ... O3voa?dl=0
You'll need to get a hold of some dental elastics. Make sure that they are 6 to 6.5 onzes. The Falcon hand uses size 3/16, but I think this design needs 1/4.
All feedback is welcome. This design had some very nice useability and installation advantages over the current design, but we need to look for drawbacks. I don't really feel good about giving this to a recipient yet, but maybe a few people would like to print one out and see what they think.