The combination of yarn volume increase with yarn length decrease results from the helical structure produced by twisting the yarn. A child’s finger cuff toy, which is designed to trap a person’s fingers in both ends of a helically woven cylinder, has an analogous action. To escape, one must push the fingers together, which contracts the tube’s length and expands its volume and diameter…
Muscle contraction – also called actuation – can be ultrafast, occurring in 25-thousandths of a second. Including times for both actuation and reversal of actuation, the researchers demonstrated a contractile power density of 4.2 kW/kg, which is four times the power-to-weight ratio of common internal combustion engines.
To achieve these results, the guest-filled carbon nanotube muscles were highly twisted to produce coiling, as with the coiling seen of a rubber band of a rubber-band-powered model airplane.
When free to rotate, a wax-filled yarn untwists as it is heated electrically or by a pulse of light. This rotation reverses when heating is stopped and the yarn cools. Such torsional action of the yarn can rotate an attached paddle to an average speed of 11,500 revolutions per minute for more than 2 million reversible cycles. Pound-per-pound, the generated torque is slightly higher than obtained for large electric motors, Baughman said.
It’s fun to ponder the potential applications of this sort of technology to the space environment.
One application in particular jumps out at me: surface suits. Part of the problem with mechanical counterpressure suits (what the skinsuits in In the Shadow of Ares are) is getting a good fit with sufficient pressure over the whole of the body and maintaining it as the wearer moves about. In most areas of the body, particularly convex and shallow-concave areas, this can be accomplished with the correct choice of weave and orientation of fibers and seams along the body’s extension lines, etc. In concave areas, “packing material” is required to fill in the spaces and transmit mechanical pressure from the textile to the body surface. As this might suggest, MCP suits as conventionally conceived are still bound to require substantial tailoring to the individual wearer and substantial time to don.
What if, instead, you had a textile that could contract or relax, locally, on demand, on the fly?
The obvious improvement would be that the suit could (with embedded/integrated sensors) continually adjust over its entire area to maintain a constant mechanical counterpressure in all areas (perhaps more or less pressure in certain areas as research might demonstrate to be desirable), even as the wearer moves. This might, among other things, reduce suit-imposed limitations on range of motion while eliminating bunching and pinching at the wearer’s joints. A self-adjusting textile with enough range would reduce the need to specifically tailor suit components to a specific wearer, allowing the wearer to choose components or whole suits from a range of standard sizes and then “shrink fitting” them after donning.
Naturally, if such materials were used in this way there would have to be some built-in safety features – perhaps in its passive/non-energized state the textile would still place enough pressure on the wearer in enough areas to avoid physical damage. Or, akin to what we describe in a few places in the book , the main benefit of the muscle textile might simply be as an aid to donning and doffing the suit (apply a current, the suit relaxes, and normal zippers can then be closed or opened more readily and rapidly than otherwise).
The material’s ability to rapidly stiffen with much more force and speed than human muscle reminded me of the impact armor from Ringworld. If a suit were engineered with this muscle material oriented such that it could actually move the wearer (think of powered armor that works both ways), not only might such a suit be able to directly protect the wearer from impacts (up to a point), it could simply avoid the impact by moving the wearer out of the way. A sufficiently intelligent system might “control” their limbs in (say) a fall, moving them against instinct or with more strength than they can normally muster so as to assume postures that will slow them down, protect the head, etc. or even grab something to stop the fall.
Beyond such contingencies, just imagine what a powered suit like this, coupled with sensor and processor technology capable of reading and amplifying one’s movements in real-time, could do in everyday use for someone with reduced mobility…an application which, it happens, ties in nicely with a short story idea Carl and I have been knocking around.