Thank You All for the kind words!
I'm happy with the results as a first run, but there are a few small tweaks, the main one is the drilled holes, they need a starter bit first. One bit in particular walked way too much and I didn't think it would turn out so well. Also, the v-cuts were MUCH deeper for the bends than I had intended (.005 inches is what I wanted, but didn't zero my tool right), but it made the bends nice and square.
This has been a very slow moving project, as I've spent most of my spare time in software.
The goal here isn't as much a "grasping" hand as it is an "expressive" hand for communication. People talk not only with voice (which is something else in my plans), but often communicate with their hands as well.
My goals for this project:
* Small Hand in similar size and shape to stock Robonova 1 hands when clenched, but matching look and feel of the Robonova 1.
* Aluminum bracketry with a hint of black plastic like the Robonova 1.
* Full finger articulation for all kinds of subtle and not-so-subtle finger motions.
Regarding Melissa's God Hands: Yes, they're way too expensive. And with fingers made of u-channeled aluminum, not easy to make. I went with Igus E-Chain, as it fits my application well and reduces the work of designing and building fingers by hand. The insert blocks (all same size / shape) are the only modifications for the e-chain.
These will cost me approximately $400 USD in materials when done for one pair of hands, but this is just for servos (most of the cost) / materials in the finished pieces. I have my own CNC machine, with a few thousand USD invested in that, along with "disposable" material costs for trial and error, etc.
It could hold a thick pen in the 4 fingers, but that isn't really why I'm building them.
The thumb is more aesthetic and not so much to be functional.
The servos in these hands are MKS DS450 servos, high torque (3.1 kg/cm), metal gears, very small, very narrow for the torque they put out. I looked at many servos on the 'net, these were the best choice in the end. The other issue is travel, and too small means less travel for tendons. These servos are "just right" for a few reasons. Just realized, 15.5 kg/cm per hand... Wow.
I will be using Pololu servo controllers in these, and I have both USB and serial versions to test (it's the smallest size of each version). This will mean I have 3 wires to the hands, 1 data and two power (the Pololu boards don't need to talk back to the controller, a Roboard RB-100 in this case).
It's my intention to build two working sets for two equally equipped bots, RN-1's, 1 in Red and 1 in Blue. The hands will either be Anodized or Painted, and I may end up doing both before it's over (painting now, anodizing other sets later).
I debated over fingers a good bit before I started. If I built fingers by hand, it would certainly not be easy to make. And, going with E-chain guarantees smooth and stable motion (no play in joints), as well as low operational friction allowing me to use .020 inch teflon for tendons instead of nylon - less torque needed in the servos to make it work. And more, the e-chain fingers are light weight. I'm already adding a lot of weight with the servos, so better to save a little weight. On top of all this, the fingers have a "thick" look I haven't seen in alu Melissa Hands - the ones I've seen look thinner, more slender - I wanted fatter fingers.
On top of all of this, the bends of this size e-chain very closely matches the profile of the stock Robonova 1 hands when clenched.
Drawbacks of e-chain? It's not metal - but it's tough, designed for innumerable cycles of use in their intended application, protection of wiring in a moving system. That said, they're not extremely strong. I think they're plenty strong for my application, but I haven't had to catch the force of a falling Robonova 1 with them yet. If I do snap one, replacing links of chain is easy - even the insert blocks can be removed, they just rest inside the chain, captured with their top channel cut.
When this is all together, will he be able to hang from his fingers? I don't think so!
But, if his fingers get jammed, they'll either snap at the links, or worst, tear the teflon tendon - both easy and cheap to replace. The teflon is thin enough that it will probably tear at one of the mounting holes before the servo gears break. I do think he will be able to do cartwheels, as the strength then is in the e-chain when bent, not the teflon tendon.
I have a few more prototypes to make to get dimensions and manufacturability straight, but there's not really that much to do on the design at this point.