Author Topic: Realistic Mecha Tech  (Read 2545 times)

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Offline harold

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Realistic Mecha Tech
« on: October 14, 2012, 04:52:06 pm »
With robotics being what it is today, why aren't there giant mecha's yet? So I started thinking, can we build them right now, with current tech?
And I haven't really encountered that much trouble, but then again, what do I know.

So here's a rough outline of my current idea, feel free to poke holes in it or, preferably, suggest something better:

Based on the following, I went for an "all-electric" approach:
- hydraulics: not too bad speed/strength, but angular range of motion of a joint is terrible. Acceptable precision.
- pneumatics: very fast, can have speed and precision trouble and the range of motion is still terrible.
- mechanical drive (connecting actuators to the main engine with pushrods or pulleys or whatever) is probably the worst option.
That leaves an option which doesn't seem to bad: electric torque motors everywhere. With a large radius, and active cooling (fluid-cooling for the high power parts such as knees, hip, elbow, shoulders, air cooling elsewhere). I did some calculating, and with current tech you can easily make your mecha strong enough with torque motors. I know, it's weird. But let's see:
Let's take one from this list, just to prove the point: http://www.etel.ch/torque_motors/TMB
A diameter of 80cm is acceptable for a 5 meter tall mecha (that sticks out only 40cm at each side of the joint, and that doesn't look as bad as you may think it does), so let's take the strongest one of those: 6.4KNm continuous, 11.2KNm peak. Let's put in the most demanding place, the knee, and assume a worst case angle of 0 degrees, and assume both leg sections have a length of 1.2 meter. That means your mecha can weigh about 550kg. WTF? Not good enough! No, but no one said you had to use just one. While it has a diameter of 80cm, it has a width of only 15cm. You can easily use three (or heck, why not four), giving you a max weight of 1600kg. That's more like it, and remember: you don't do this. This worst case corresponds to squatting on one leg. Why would you do that? You actually have two legs, and you're not even going to squat to zero degrees when preparing for a jump - and when you're jumping, you can turn the dials to eleven and use peak-torque, which is nearly twice the continuous max torque. Unless my physics suck (not entirely out of the question), this will work out just fine in terms of raw strength. You should be able to jump, run, climb and throw one hell of a punch.

Then there's the issue of power supply. Carrying around a generator and a flammable liquid works alright and is the usual solution, but if you look into Aluminium-Air batteries there is something to talk about there too. Alu-Air batteries have a lower energy density (9MJ/kg according to some sources) than, say, diesel fuel (45MJ/kg), but that's not the only factor. For Alu-Air, you don't have an engine and a generator, and that space is not insignificant - you'd need a pretty sturdy engine and generator. Also, being a battery, mechanical failure is unlikely unless moderately damaged, and it works great under non-constant load, which is what you'll have in a mecha - running, jumping, punching, etc? Such great bursts would require energy storage to smooth out if you went for a combustion motor + generator (unless you used pneumatics, which I chose not to).

Slightly into future-tech: both battery tech and electric motor tech are improving as we speak. These are active area's of research. If it works well enough now, imagine how well it will work a decade from now, or even just with the latest research models.

Now, the controls. They have been subject of much debate. Those "hands and feet only" style controls (joysticks and pedals, seriously?) don't offer nearly enough degrees of freedom - the entire idea is to have a tactical unit that can do whatever the heck, not just a "tank with legs". I think the best option here is keeping most of the body immobile and sensing the muscles of the pilot. That also lets you give the mecha more flexible joints than the pilot has - it senses which way you want to move a joint at what strength, not where you want to have it, so it could easily "go further" than a human joint. That's also no problem at all for a torque motor. It shouldn't be too hard to train for that. Taking such direct control also means you don't need very complex "walking algorithms" and systems to keep balance - the pilot should be able to do it himself, using his natural instincts, feeling for balance, and some training.
We're not quire there yet with reading input directly from the brain, but we're eerily close. That's the sort of tech no one knows exists - it does, but it hasn't, to my knowledge, been miniaturized yet, and the response times are bad.

That works great for legs and arms, but not so much for hands. There, you'll want tactile feedback, and that sort of tech already exists as well. Also, you'll need some way to control "other stuff" (turn night vision on and off, climate control, weapon systems, etc). So I propose that your left hand (or right, if you're a leftie) doesn't control a robotic hand but instead manipulates a touchpad. That makes the left arm of the mecha a good place for fixed weapons (no lasers yet, but a nice gatling gun should work), which may seem odd at first, but you'll get used to it, and you could still hold a weapon in your right hand. I'm not 100% satisfied with this approach though, so if you have a better idea, that would be great.

Sensors (vision etc): you'll want this to be good. I'm thinking stereoscopic projection on the eyes, with extra info overlaid (also the virtual buttons and stuff that your left hand manipulates, if you can't see them you can't find them), looks around when you turn your head. And you know the drill: can zoom well, can draw boxes around targets, has infrared mode, and generally tries to provide useful information without getting in the way. That already exists, too.

So, thoughts? Is this even on the right track?
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Offline Rhombicuboctahedron

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Re: Realistic Mecha Tech
« Reply #1 on: October 14, 2012, 05:53:51 pm »
Why would we want a giant mecha anyway?
Yeah, the idea is cool, but it would cost a heck of a lot to make.
It doesn’t have much use either. It can’t go through small doors. And it would provide a large target.
Also, the only thing that would make it better than an Abrams would be that it could scale buildings and mountains.
And it would cost much more.
But sorry, I don’t know much about the engineering.

Offline DJ Omnimaga

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Re: Realistic Mecha Tech
« Reply #2 on: October 14, 2012, 06:02:41 pm »
Just make sure it can't be flashed/hacked so that it won't do like in Terminator 3. :P


Offline jwalker

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Re: Realistic Mecha Tech
« Reply #3 on: October 14, 2012, 06:07:38 pm »
It would be spendy, but completely awesome
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Offline lkj

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Re: Realistic Mecha Tech
« Reply #4 on: October 14, 2012, 07:08:41 pm »
I think you're underestimating keeping balance. It's only possible for us humans because we can move every part of our body. If the torso of the mecha couldn't bend I don't think it would be able to walk well.

Offline harold

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Re: Realistic Mecha Tech
« Reply #5 on: October 15, 2012, 06:26:28 am »
Balance could be an issue yes.. I don't think it's really necessary to make the torso bendable in a complex way though, you don't really do that, you only bend your lower back (and I'm not sure you're even supposed to). A suitably complex hip should be fine, I think.
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Offline TIfanx1999

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Re: Realistic Mecha Tech
« Reply #6 on: October 15, 2012, 09:32:04 am »
It also depends on how the mecha walks and how much diversity you want in it's motion. Most likely it would not walk like a human would nor have near the amount of diversity or complexity in it's motion. I don't know about a giant mech, but something more like an suit in the old exo squad cartoon or a loader type mech like what Ridley used in the Alien Series would definetley be plausible.

*Edit* For a newer example, I'd cite the Mechs in the movie Avatar.
« Last Edit: October 15, 2012, 09:33:35 am by Art_of_camelot »

Offline Builderboy

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Re: Realistic Mecha Tech
« Reply #7 on: October 15, 2012, 04:00:50 pm »
You should check out the Sarcos XOS, it's basically what you are talking about, and it looks super cool :D

Offline harold

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Re: Realistic Mecha Tech
« Reply #8 on: October 16, 2012, 05:25:57 am »
XOS looks cool yes. They use hydraulics, the only other realistic option (as far as I know). And they're having trouble making it self-powered, as I predicted, though going for the exoskeleton configuration makes that harder than it would be in a giant mecha.

edit: and I just thought of something. The large inner diameter of torque motors makes it possible to fit a simple robust planetary gear in there. For example, fix the sun gear to the upper leg, fix the carrier to the lower leg, drive the annulus with the torque motor. This simple arrangement can give you a 2:1 reduction (at best) in speed, and therefore a 2x increase in torque. What if we used a smaller torque motor with gears? Suppose we use three of them in a knee, same leg size, and go for a worse case angle again. Some math later, that gives (6 * 2700 newton meter) / ((9.81 m/s^2) * 1.2m) = 1.38 metric tons of holding weight, and at max torque it can "jump" with an acceleration very close to 1g. Is that good enough? I don't know. Let's put in the bigger model again, the 79.5cm one: if you use three, you get a holding weight of 3.24 metric tons. Now, I don't really know what the weight of this mecha will be, but that seems about enough - with plenty to spare for "carrying big things" even at that worst case angle. Or, put differently, if you put that specific knee (3 times the 79.5cm torque motor with a 2:1 reducing gears) in a 1ton mecha, you could make a jump of more than 5.7g. That's some jump. This isn't some slow lumbering giant, it's actually one of those crazy agile unrealistic mechas that you see in anime. Assuming, of course, that you can keep the weight at 1ton.

edit2: I made a quick rendering rendering that took a ton of work (it is in fact exactly to scale) of what a 16:9 (about as close as you can get to 2:1 with sturdy enough gears) gear system would look like

Now imagine a torque motor on the outside of that, the three small gears being connected to the inner framing of the lower leg, and the middle gear being connected to the inner framing of the upper leg. The large hole in the middle gear allows you to fit cables through an area where the cables only have to move minimally when the joint is turned. So far this seems to be working out well.
« Last Edit: October 17, 2012, 03:13:54 pm by harold »
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