Prosthetics have existed for a long time, because for much of human history, people have been losing parts of their bodies and yet wanting to continue getting around and handling objects around them. The archetypal prosthetic is the peg-leg.
Over time, prosthetics have been getting more and more sophisticated (although, unfortunately, also more expensive). They've gone from simple rods, to finely articulated limbs that respond to small changes in the wearer's posture, to powered machines that respond to muscle potentials and allow the wearer fine control. There are also a few made of high-tech composites and such, using the strength and elasticity of the materials rather than electrically-driven hardware, to provide function. But I'm more interested in the powered, muscle-controlled prosthetics.
Electromyograms (EMGs) are readings of the electrical activity of muscles as measured through skin. These are probably one of the most common ways of controlling powered prosthetics, because they don't require any implants of electrodes or grids or whatever; the sensors can simply be held against the skin, by glue or the pressure of straps. Readings from the electrodes get fed to a controller, processed by the algorithms it's programmed with, and then turned into motion by some form of actuator.
Turns out there's not simply electrically-powered prosthetics, but steam-powered ones as well, using a peroxide-catalyst system vaguely reminiscent of a bombardier beetle's defenses (see flaming skunks). The advantage of steam is that its power-to-weight ratio is very high, compared to batteries; the disadvantage is that the tolerances required in the valves are on the order of one micron, apparently a difficult level of precision to achieve and maintain in a steam engine, plus the power source needs to be replaced or refilled (not simply recharged, like batteries) after 18 hours' worth of activity. So you need to spend a fair amount of money building the thing, and you have to buy a new fuel canister more or less every day, unless you have a home hydrogen peroxide manufacturing kit.
Now, a steam-powered prosthetic arm is awesome and mad-science-y enough, but I want to go one step further. Using this technology, you could probably create extra limbs for yourself. The difficult part would be in learning to control it. And here's where homebrew EE/ME comes in.
For example:
A long time ago, I read a set of instructions produced by a costume-builder, instructions for building a wearable, articulated and animate tail. His design is worn attached to a belt or harness and controlled by an easily-concealed keypad, fed through a computer about the same size as one's thumb, with the additional ability to generate random movements, should the wearer so choose. Now, this is pretty clever; his design is intended to mimic the way living animals' tails are articulated, with servo-driven cable "muscles" linked to spines protruding from the individual tail segments. The cable sets are arranged in pairs; a left-right pair, and a forward-back (or adductor-retractor if you prefer) pair.
Pretty clever, right? There have been modifications suggested (not necessarily directly to him, but on the internet generally) to replace the keypad controller with accelerometers that would respond to the wearer's changes in posture or his stride; with some rewriting of the control software, this would allow a posture- and gait-reactive set of movements.
I'd suggest going one step further.
Most tetrapods' tails move in concert with some of the large back muscles, correct? This is how the tail can wag the dog. Possibly an even more effective way of building something that reacts to the posture and gait would use EMG readings, as described above. Readings taken from electrodes pasted or strapped to a wearer's lower back could be used in place of accelerometry readings, with a corresponding rewrite of the code in the controller.
So what does this mean? It means that, in addition to the uses of EMG control for prosthetic limbs, it could be used to control additional limbs through clever use of bracing, harness and (non-cosmetic) corsetry. Here's what I imagine.
- Construct a wearable harness, including a tough carapace, that doesn't move over the wearer's body when shifted this way or that. (The carapace is to keep leaks or explosions from catastrophic equipment failure from injuring the wearer.)
- Fit artificial limbs into the harness - for example, a pair of steam-driven arms - in such a way that they can be useful to the wearer. The precise design and arrangement will depend on what the wearer can be expected to do during his work-day, of course.
- Connect the limbs' controller(s) to EMG electrodes held in place by the harness or, in extreme cases, implanted under the skin. Train the wearer in their use, which might extend to deliberately tensing or relaxing specific muscle groups in order to trigger a response through the electrodes.
- ???
- Profit.
This could be used, for example, to allow a human worker to handle larger pieces of equipment, things he couldn't properly control or wield with two hands alone due to their shape and size. For example, a larger and more powerful Hurst rescue tool, or two at once.
I have too much time on my hands. Can you tell?
(Many thanks to Wolfgang Tail for the inspiration.)
(Other diaries in this series include virtual worlds, robot safety, ye short fiction, the sociology of fictional places, steam-powered giant robots, thermal depolymerization, nuclear airplanes, psychic powers, transgenic bacteria that make useful compounds, lightning in a jar, neural interfaces, powered armor, sonic weapons, rapid prototyping, putting Mentos and Diet Coke to good use, life on life support, combining farming and electrical generation, pigeon pilots, cuttlefish behind the wheel, the hafnium bomb, and building a better skunk.)