There's probably some engineers somewhere who thought of them, but I had a few ideas for various things: Instead of directly motorizing joints or using hydraulic pistons for exosuits/exoskeletons, why not mount motors where it's convenient and use the same system that muscles use by attaching the wire on the target limb from the front of back? For instance, leg movement. There could be four, six motors mounted on the thigh - two or three per direction. Each motorized group drives a spool/arm to which some steel wire (possibly knotted if it's a single strand for both directions) is connected - one anchor point about two or three inches below the front of the knee, one anchor in the middle of the calf at the back. The motors move the bar/wheels, which pull at the limb. More efficient than motorizing joints, less bulky than pneumatic/hydraulic systems. It would still need a power source, but unless I'm missing something a good power pack could power it for a few hours (or maybe even a small streamlined engine, or something related to my ideas below) considering that, since it doesn't pull close to the joint, it should require less power to do work. Plus, with this system, it should be relatively easy to implement a lock system - just immobilize the bar or wheel and the thing stays as it is, without needing power. And for heavier applications? The motors, instead of driving the pulley directly, drive a flywheel - for instance, on legs, the flywheel to put the legs 'down' could rev up while the leg goes up. And I'm not entirely sure that it's not possible to use gravity or inertia to have regenerative recuperation somehow). Another idea is general spring-power. I have no idea how efficient or energy-dense it would be, but I was thinking we could use springs (considering we already use flywheels) for energy storage. For that, I specifically thought of a few nested or stacked torsion spring designs. The first one was, in essence, solidly linking the ends (middle or outer) of oppositely-placed torsion springs (because I noticed that, in torsion springs, linking two aligned springs is much like moving the middlepoint of two stacked linear springs) and continuing to place them in series to make what is, in essence, a more compact and manageable but still huge torsion spring. Varying the girth and length of springs could power different applications - you could place a 6-inch spring along almost the whole length of a car, connected to a gearbox. Rewound by a port at the front, and it EASILY could implement regenerative braking by having a system either have another, lighter drive bar underneath it that feeds the spring back when the drive is disengaged and the car is still moving, or simply having a system put the gearbox in reverse while trying to stop. A smaller but wider two-layer spring, coupled to a small gearbox (or flywheel system) to produce power. Third idea was for several form of wheel-motors for vehicles, and how to make them usable in areas laden with potholes, or offroad, or other suboptimal conditions. I probably have the concept drawings somewhere... Also, somewhere I have some documents on theories on how we could make cars that handle like the ones in 'I, Robot'. Along with a nifty three-wheeler three-to-five seater sedan concept to go with it, including a few configurations (most of them electric, but I managed to klugde an engine drive in there somehow - most of the ideas on having universal steering aren't friendly to driveshafts) ALSO, I once thought about the EMdrive and I realized that the reason why it might just work is because of radiation pressure - it literally uses photons/an electromagnetic field as a propellant (since it's open only on one end, IIRC, it pushes asymmetrically on the container which causes thrust - the particular shape might just be the ideal shape for containing and amplifying (perhaps even causing resonance) at the given frequencies. And if that's the case - pumping enough energy into it might just make it a vacuum laser). Also, while I didn't have the mathematics down and there was a few flaws, I came to the conclusion that the reason our mathematics were all wrong is because we adhere to a vehemently cartesian point of view - while we should at LEAST use a polar, if not angular point of view - since everything is relative, we should use relative measures (and from close enough, any curve becomes straight, and because of optics any 'straight' line is actually the curve to an unfathomably large curve (and that was also the solution to the coastline issue - it's not that the coastline was infinite, it was just that our measurements weren't curved) that changes according to your point of view - and constant velocity in a straight line just does not exist in the universe - anything going at a constant cartesian speed finds itself either accelerating or part of a curve around something). Then I realized that most, if not all astronomical (including GPS) calculations were made by using angles... and converting it to cartesian metric when possible. Another of my musings: there is life, in the galaxy, without any doubt. However, I learned somewhat recently that relativity broke simultaneity - which means that, if FTL is truly impossible, the reason why we never have and most likely never will encounter alien life is that for all we know (and I'm pretty sure it's the case, considering the whole galaxy spins like a disk instead of like orbits) the other star systems/the whole galaxy is going 'faster than c' in classical physics, which means that we're all going at relativistic speeds, which itself means that it's not impossible that by the time anyone gets anywhere (even at close-to-light speeds), everything has already either died or left... which is also why I do not believe that extra-solar colonies will, at best, become a new Earth (because by the time they get there, Earth will most likely be vacant again) and they most likely will have tremendous issues, if not be unable, to contact the other colonies. At worst? Well there IS a theory about extra-terrestrial origins for humans... On a more lighthearted note, it just makes more sense to me that the velociraptor (and other feathered raptors) had them for aerodynamics and controls (I mean - if I had to design a vehicle that couldn't entirely depend on traction, had to deal with very rough terrain and had to make relatively sharp turns at 60 km/h, plane control surfaces DO seem like a good idea even if the thing isn't going to fly). And on an even more 'lighthearted' note, the song "What if God was one of us" never EVER mentioned that if God really was roaming among men, he could totally be an African warlord, the President of China, a Saudi oil tycoon or the CEO/a chairman of Wal-Mart/Monsanto/Exxon depending on how fancy he felt. Or he could be a famous actor ... OR maybe that song was not just a song but a statement, and God got tired and passed away in 2003 who knows. Just saying - if God was roaming among men, it doesn't mean he's going to be an average person.
1. Yep, that is pretty much how finger movement would have to be done. And probably other joints where practical. 2. Springs have a very poor energy density compared to other methods and this would not be practical. Relevant here to point out I have a BSME degree. Sorry. 3. EMDrive: Probably doesn't work. There needs to be a lot of evidence before it can be accepted. Photon propulsion is well known, the problem is that they are claiming a much higher force / efficiency than could be achieved with radiation pressure. Which is why it basically appears to violate the first law of thermodynamics. 4. " I came to the conclusion that the reason our mathematics were all wrong is because we adhere to a vehemently cartesian point of view " There are at least three statements in that sentence that are totally incorrect. 5. Relativistic speeds. We are going relativistic speeds - relative to the other side of the universe. It's moving away from us at nearly the speed of light and we are from it. Look up the Hubble Constant.
1. That's mostly where I got the idea, really. That's how most of our muscle groups work AFAIK. 2. I figured as much. Still a fun thought experiment. 3. I know it probably doesn't work. I'm saying that if it does, that might at least partially explain why. The EMDrive's shape would be to light what the cone shape is to chemical propellant. 4. Never said I was correct - that was me delving in things beyond my comprehension most likely. 5. Will do. Thanks!
The leg-joints solution you've described is pretty-much exactly how it's done in the Rex exoskeleton (I worked there a few years back).
The actuator motors push and pull like muscles do - 10 in all, 2x2 for upper leg, 2x2 for lower leg, and another pair near the hip for lateral motion. The motors were made by the same crowd that made the motors for the Mars rovers. Hydraulic power is out, due to risk of hot fluid / patient proximity, so it's all-electric. No actuator wires though (motors were directly connected to the skeleton), there were enough problems with system-slack as it was; wires would make the problem worse (it's critical to know physical leg position pretty exactly).
Not saying actuator wires, though. I'm saying wires attached to actuators - the actuators pull the wires, and instead of pushing back, to do the opposite movement you pull the opposite. Except that I can see actuators being a bit harder to use, so I was thinking more along the lines of a stepper motor assembly driving a bar (not unlike bicycle brakes) or a pulley (not unlike securing cord on flatbeds) that would pull the steel wire. Though I'm glad I actually did figure out something that actual, certified engineers have been using. Makes me feel clever.
I got what you meant; maybe I wasn't clear. The problem is that wires stretch. These are stepper motors.
Now I have a question. Just how much weight/force is involved into that suit for steel wire/cable stretch to be a considerable issue?
I'm a software guy so this isn't my area of expertise; I can't give you a numbers answer. The motors are quite powerful though, they can easily break bones, so user-safety was an important concern (especially since most users of the devices had no feeling and wouldn't know they'd been injured right away). However, in general terms - you command the motors to go to a particular position and stop; in zero-G, that would be the end of the story, but under gravity, there will be "sag" or "slack" in the system - it moves a little bit. It takes very little difference between "where I am" and "where I believe I am", to affect the machine's balance. Every linkage adds a bit more "looseness". As far as I know, wires were never even considered, because it's a pretty high-spec'ed wire that doesn't stretch at all. Hope that makes sense.
That can't possibly right, though. No matter where I look, the math doesn't support it - using 1x7 galvanized, according to this page, and assuming an extreme load of 600 pounds, it would still only stretch by ~0.01% of the cable's length - which, for a cable of let's say 18 inches for measurement, has about the same stretch as it has diameter - a quarter inch. For stretch-proofed cable, this calculator (assuming eighth of an inch diameter, 18 inch long 1x7 cable and generous 120 pounds-force load) gives an even drastically insignificant stretch - 4 millimetres. And unless they used slow, screw-gear actuators, I'm pretty sure that the inaccuracy is in similar numbers.
It would need to be accounted for, sure. I'm not saying it's not. But it's accountable for. And hence why I say it's not an issue. Hell, the control systems might not even have to deal with it if you design your thing so that the cable stretch is beyond negligible. Then again, I realized we were talking about two completely different systems. He was talking about exosuits to practically replace people's mobility. I was more thinking of strength amplification where the suit makes your movement stronger - but the accuracy is still governed by the human.
I'm not a mech, but 4 mm is far from insignificant. Also, you'd probably be surprised at how much force goes through the hip joints - I don't know the numbers, but that hip joint really had to be made tough. We destroyed a number of them.
4mm out of 460mm is not insignificant? It's less than 1%. Most people I know would call that number a rounding error. As for how much force goes through the hip joints - I am aware, that is why I was suggesting to apply the force away from the joints. Do you not know of the lever principle?
This is going to get you into trouble: you're talking to someone who was actually involved in systems very similar to your ideas, and is giving you boots-on-ground examples of why the things you haven't considered are preventing your ideas from becoming reality. Your response is to argue with his reality. I am a mech so I'm going to give you some homework. Take a look at your hand. In particular, take a look at your index finger. Point it, then make a fist. Take note of where the extensor tendon anchors to your wrist. Point your finger and measure from your wrist to your second knuckle. Now make a fist and measure the same distance. What percentage difference are we talking about? I measure about 4 1/2" and about 5". That's a difference of about ten percent... and that difference governs 90 degrees of flexion of the knuckle joint. 1% stretch, then equals a loss of ten degrees of precision in positioning your finger - that's parkinson's territory. And that's just a finger. Imagine trying to run if you could only plant a leg within about 10% precision. Beyond that, motors don't lend themselves well to linear torque. As demonstrated, your total flexion for a rotational motion of 90 degrees is about ten percent... and the distance extended is handled much better by a linear ram (ANY linear ram). Motors are designed to spin, not rotate through a limited arc. And if you're actually moving your cables enough that they're being spooled, they've just become braided or twisted and are undergoing substantial deformation, which means their failure rate just skyrocketed. briandmyers didn't have to tell you this. He's seen it and knows there are problems. He's worked on this, and he's a clever dude. You, on the other hand, chose to dive into sarcasm in a comment thread where you disavow MATH for fuck's sake. You can choose not to believe in math but I'm here to tell you, friend, math believes in you... and when you whip out "the lever principle" in a discussion of mechanical engineering in which you don't know the players, your interests are best served by not being a smartass lest someone comes along to demonstrate your dearth of knowledge.
It's not going to land me in trouble for a few reasons: first, I don't particularly plan to implement those in a lifetime. Second, and it's something I apologize for, there's a point I overlooked: I realized that we were talking about two completely different applications. He was talking about replacing an user's mobility in medical fields. I was talking about augmenting an user's already existing mobility - this idea was mainly to amplify the strength of an user that already had full mobility. As for that stretch - that's 10 degrees only if you use a very basic driver. The wonderful thing about electronics is that you can account for that stretch. Or you could use materials science and use, as I mentioned, pre-stressed cable that does not stretch as much, or even design your system so that the cable is already under a tension high enough that any further stretch is even less of an issue (though I do acknowledge that this is not a fail-proof execution either). And as far as your example go - I also have issues with it. The one percent stretch I mentioned was in the case of an extreme load on a thick cable at a very high weight - something that would be found only in very overweight people or military applications. The aforementioned finger would, in all likeliness, never even reach 0.5% of that load. Using that same linked calculator, with a 6-inch 0.11 inch cable under 30 pounds-force of load, it's 0.02% of cable length - an accuracy of about 0.018 degrees, which I do believe is on par, if not finer than human motor control. For the motor issue, I'll give you that - but with a stepper motor (or an array of stepper motor) you could have enough control to make it useful. And I used the term spool to refer to a circular thing that turns and affects the "length" of a cable - or, as I mentioned, a bar. As for the "lever principle" thing, it was not sarcasm. I have honestly seen people with higher education, like software engineer, that forget about such basic principles. And I did not disavow math - math is the only thing that matters in engineering - I just consider all the options, like actually designing things to avoid the bigger math problems like stretching. But yeah - the lever principle comment was not sarcasm - it was merely to ensure that we had a similar knowledge base. It's not because he's clever that he didn't forget about things. Sorry if I came across as a smartass.