Probably the most well-known exoskeleton suit is Iron Man.

Iron Man

In concept, you'll usually see Exoskeleton suits with either tight-fitting joints (perhaps similar to plate armor, I'm not sure), or, you'll see a mess of wires and occasionally gears. One thing that is naturally ignored or not explained well is the weight that such a suit would have. Supposedly, the person inside can lift his leg just fine.

Sometimes this is attributed to light-weight armor - making the suit almost more like high-tech all-encompassing military combat armor.

Other times, the person inside is actually pushing against sensors that trigger the suit to move in the desired way via mechanical motion. Gears, Hydraulics, etc.

My question is strictly covering the second case. However, also keep in mind that there is a human arm and leg in there - I'm not aiming for a pilot who controls the appendages while sitting in a cockpit.

How would the mechanical connections of joints (primarily those on the shoulders, hips, and knees) actually function to power the limbs into the correct positions, while staying somewhat true to a humanoid shape?

  • 1
    $\begingroup$ It seems to me that the joints wouldn't "power" the motion so much as allow it to happen without causing undo friction. Much like the human body, the joint's purpose is to bend, and the "muscles" pull on the joint from either side. $\endgroup$
    – Lumberjack
    Aug 1, 2016 at 20:48
  • $\begingroup$ Yet, the armor of the suit would still (most likely) encompass the "muscles", would it not? Like skin over our "joints"? I guess I'm trying to understand the mechanical methods we have available in order to create the motions involved while being able to stay armored, even if those methods wouldn't (today) be "powerful enough" $\endgroup$ Aug 1, 2016 at 20:57
  • $\begingroup$ Have a look at en.wikipedia.org/wiki/Artificial_muscle $\endgroup$
    – Aify
    Aug 2, 2016 at 6:13
  • $\begingroup$ This question is insufficiently researched before asking. $\endgroup$
    – JDługosz
    Aug 2, 2016 at 10:37
  • $\begingroup$ @JDlugosz I suppose looking for the right terms (actual products rather than a science fiction angle) would have helped. My searches yielded a lot concept art by artists who either put gears and wires where the arm should be or expected the person to power the suit. $\endgroup$ Aug 2, 2016 at 15:39

3 Answers 3


There are three basic options available.

  1. Hydraulics/Pneumatics: A push/pull cylinder on one side of a joint will give you the movement. Leverage is of course all wrong but it is with a human body anyway.

  2. Joint Servos: Servos are standard kit for certain tasks but they tend not to be massively high powered. Good enough for a bit of force multiplication but not up to full blown power armour.

  3. Artificial Tendons: A motor or servo pulling a cable on each side of the joint to give movement.

In all these cases you need to model the joint first. What degrees of freedom do I need? How can I most effectively generate that movement while staying within the range of movement of the body underneath?

Consider the ankle; two degrees of simple movement and a bit of rotation in the lower leg. The rotation can be displaced upwards so you only need to worry about the pitch and roll in the joint itself which can be done with a compound of two joints.

I'm assuming you're going to largely immobilise the back and neck, so your most complex joint is the shoulder, but even there you can run the a similar model to state both the freedoms and limitations on the movement.

Power supply is the problem though.


First, this doesn't exist in real life because we don't have the technology to make it that powerful and that small. Cosplay suits are either powered by human movement or are bulky enough where this isn't an issue. However handwave a few decades of development and you might be able to do this on a military level.

High-powered servo motors allow for this movement, with multiple attaching to a gear that is affixed to the pivot point of movement. I can't find any hard numbers on torque for robotic servos, but back when I did robotics (as a hobbyist, with hobbyist grade servos) you could get them where it was a bit of tug-of-war to fight them spinning a wheel, and they offer <1 degree precision. Right now they're about the size of a small tin of breath mints, but in our 20-30 years we should see this size fall and the torque increase.

...And there you have it. It's really as simple as that. As time progresses we'll be able to miniaturize the technology while increasing performance, and then it's not much to hide on the suit.

Edit: What's of bigger concern is the power source, as that's a huge concern in robotics and would be a big ol' lump on the armor. But that's outside the scope of the question, I suppose.

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    $\begingroup$ Power source is not the only concern. How about cooling of the systems? Since there is a living person inside this tin can, you have to keep the whose suit on rather low temperatures. Compact cooling system is a large problem on it's own. $\endgroup$ Aug 2, 2016 at 7:46
  • $\begingroup$ Exoskeletons conveying super strength and endurance via natural motion does exist today in real life. $\endgroup$
    – JDługosz
    Aug 2, 2016 at 10:38
  • $\begingroup$ @JDługosz As compact as Ironman's suit, and supporting as dense construction? We're already there? $\endgroup$
    – Ranger
    Aug 2, 2016 at 20:31
  • $\begingroup$ No, as the OP notes the ironman joints are not realistic. He asked what real ones would look like if you actually engineered such a thing. And people have. Your answer is “we can't make something that looks like ironman's suit (without visible joint actuators) but with further miniturization we could.” which is not the question and if it was it just repeats it without answering it. $\endgroup$
    – JDługosz
    Aug 3, 2016 at 1:46

Like this:

the real thing

real thing 2

I think this is a concept exhibit not a real suit, but I like the picture for the view of the leg. You can see how the power member (with joint) is simply in parallel to the wearer’s leg.

Just look at some real products that are available commercially now, and technology demonstrations for research.

I've seen such things on TV before, and took all of 20 seconds to find via Google for “military exoskeleton”.

The Wikipedia page goes over the (surprizingly long) history and briefly summarizes how they work, and has a long list of links to actual products you can explore.


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