My mind has been coming back again and again to this idea of making a fully manually-operated version of the Elephant Robotics exoskeleton for use as a drawing tool. I got one step closer to actualizing that a few days ago when I finished this very “minimum viable product” version of one type of gripper/grabber mechanism I am calling the grabbit-1.

I have a couple videos of it in operation at the Imgur link here. Here’s a static image:

I was dimly aware that cable controls were a thing you can do for mechanical puppetry, by way of this very retro video series on that topic:

But, like many four dimensional movements, this operation I found extremely difficult to understand without actually building a prototype. (Also see this other more contemporary example of someone using clear tubing and wire for a cable controlled puppet.)

Now, obviously I’m a long way off from the Elephant Robotics exoskeleton model here, but you have to start somewhere when you’re carving up complex physical problems like this. So understanding simply how grabbers/grippers worked seemed like a good enough place to start…

I often do these like chaotic jags through hyperspace when I’m figuring out a problem like this, usually through combinations of high speed skimming across tons of YouTube videos and image searches and asking ChatGPT for the names of things or principles that seem relevant. I end up with tons of good reference materials very chaotically organized though, and thought I’d want through some of them here for my own understanding if nothing else.

I actually found this one late in the process, but it is very helpful in demonstrating disassembly and functioning of one of those gripper dealies you might see senior citizens use, and which are actually surprisingly precise if you’ve ever used one:

There is something called Bowden cables, which are what makes the brakes on bikes work that is at play here, and in a very rudimentary way in my Grabbit-1 prototype. Where a cable or wire is inside of a length of tubing, and when one end of the wire is pulled (or pushed), that movement/force is transmitted through to the other end. It’s like if you connected two pieces together by a rigid rod, except its malleable, and the tubing lets you potentially put a bunch of these kinds of control cables together for different sets of discrete or connected movements. (Also see this guy’s interesting uses of Bowden cables in some kind of marble mechanism.) But I’m getting ahead of myself.

I wish they showed the other end of the cables controlling that motion, but I suppose it must be something like the frames with rings in the retro mechanical puppetry video above.

I also realized during this process that, as cool as it is to make hands that move in a lifelike way, depending on what I ultimately decide the exoskeleton project requires, I might or might not even need them. In one sense, a robotic human-ish hand is not really the ideal mechanism to hold a drawing device… Simply clipping a paint marker or whatever onto an arm or stylus or something is in many ways easier and a more reliable – but also somewhat less “awesome” looking than the above video, or this one which rules:

This is basically the same principle for cable controls, and the cables run through eyelets instead of tubing, and then they actuate levers linked to the larger arm joints. Here’s another video showing more or less the same setup in a different configuration. (This Instructable to build giant wooden hands is somewhat similar and has some close up photos. And this one is crazy in that it translates the hand motion down to a tiny scale articulated hand that has very creepy cool vibes.)

The basic grabber mechanism also appears in another important medical context: prosthetics for amputees. Some good example videos of how that works for body-controlled grippers:

And here are some related images of various kinds of hand prostheses I threw onto Imgur for reference.

I found out through that avenue of research that there are (at least) two types of gripper mechanisms like this, what’s called Voluntary Open (VO) and Voluntary Closed (VC). In voluntary open mechanisms, my understanding is they are in a default closed position and you need to exert effort which opens the mechanism. Voluntary closed is the opposite: they are default open and when effort is applied, they close. And then in either type, springs return the mechanism to its original state/position when the cable pressure is released.

This diagram helps somewhat:

As many diagrams, photos, and videos that I checked though, I couldn’t viscerally understand how these things function until I actually built it and tried it out and saw what happened.

For my design, you can see two videos at the original Imgur link at top of post, one where the Grabbit-1 functions normally (open by default, Voluntary Closed), and then another one where based on that prosthetic video above, I put a rubber band around the gripper, so that it would automatically be closed as its default, and actuating the little white knob (a cabinet handle repurposed) would make it open (e.g., Voluntary Open).

Now I get it after building it, which is what’s so valuable about doing these rudimentary exercises. Once I can feel how each thing functions in real space, and in comparison to my body, and to the finished art pieces that I produce with them, then I’m able to really fully absorb it, move onto the next, and eventually combine them all together in novel combinations (I haven’t even gotten to gears yet!).

Couple other things worth throwing in here at the end of this largely non-linear rant: there’s a type of arm in robotics referred to as the continuum or snake-arm which moves like a snake or robot trunk or tentacle.

Bear in mind, you can build one of these continuum robots like this which operates only mechanically, meaning no motors or electronics. It’s all just based on manipulating tension on cables. Here’s another one with less complex controller, and consequent less range of motion, but with wood parts:

I find all of this shit endlessly fascinating, and feel like this is such a healthy obsession to have and explore to its fullest as I continue building robots that can survive the coming Butlerian Jihad. Honestly, I’m having a lot more fun with this lately than with regular old boring generative AI. This all feels so much more basic and fundamental, and yet, speaks to many of the same questions in the end, but with the pieces on the board re-arranged in different configurations that throw new light – for me anyway – on the whole conflagration of issues around automation and extension technologies. A great deal more to say on that another day.

Also here is the very much obligatory Star Wars Luke’s robotic replacement hand video to end on:

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