LAST month, we started a series of columns about robots—specifically, robots that don't fit neatly into the boxes defined by science fiction.

This month, we'll consider robots in your pants. No, not porn robots. Get your mind out of the gutter.

We're talking about robots you can wear—like the Mobile Infantry Power Suits of Robert Heinlein's Starship Troopers, Tony Stark's Ironman suit, the Caterpillar P-5000 Powered Work Loader that Ripley donned in Alien, or, our personal favorite, the wrong trousers in Nick Park's "The Wrong Trousers" with Wallace and Grommit. (And if you're going to argue that Wallace and Grommit are not science fiction, go find yourself another science column to read.)

We're talking about robots that are up close and personal, as close to you as your own skin. And they provide an excellent example of a future that could take a very different direction than the one envisioned by early sf.

As near as we can tell, the first sf featuring robotic exoskeletons was E. E. "Doc" Smith's 1937 Lensman series. But some actual inventions (or patents anyway) predated Smith's fictional representation by decades. In 1890, a Russian named Nicholas Yagn patented "new and useful Improvements in Apparatus for Facilitating Walking, Running, and Jumping" (https://www.google.com/patents/US420179). Yagn's invention used springs and compressed air to store and release energy. A few decades later, in 1919, a U.S. inventor named Leslie C. Kelley patented a "pedomotor" (https://www.google.com/patents/US1308675), a steam-powered apparatus that used artificial ligaments arranged parallel with the major muscles of the legs to help a person run faster without getting tired.

But it was in the 1960's that exoskeleton development really hit its stride—right about the time that Marvel first featured Ironman in Tales of Suspense #39 (March 1963). That's when the U.S. military funded General Electric to develop the Hardiman exoskeleton suit (http://www.gereports.com/post/78574114995/the-story-behind-the-real-iron-man-suit/).

The Hardiman looked a bit like Ripley's Powered Work Loader. Big metal pinchers extended from the user's hands, metal mechanical legs were parallel to the user's legs. Wearing the Hardiman enabled a user to lift up to 1500 pounds.

That sounded pretty impressive until we found out the suit itself weighed 1500 pounds. Because of its size, weight, lack of stability, and battery issues, it never got past the prototype stage.

The Hardiman was just the beginning. Since then, the U.S. Military through Defense Advanced Research Project Agency (DARPA) has regularly funded exoskeleton development. For those of you dreaming about jet packs or even the jump jets of Heinlein's Power Suits, keep on dreaming. These suits focus on more pedestrian challenges: giving people increased strength (lifting power) and endurance. Think augmented foot soldiers lugging heavy loads.

Berkeley Robotics and Human Engineering Laboratory developed Berkeley Lower Extremity Exoskeleton (BLEEX), which Pat argues is just a long-winded way of saying "motorized pants." Raytheon's XOS Exoskeleton is touted as letting one soldier do the work of three.

It would take too long to list all the exoskeletons of the "make me a superhero" variety that have been developed. They use motors, they use hydraulics, they are motorized pants, they are motorized suits. But they share some problems with each other, and with their ancestor, the GE Hardiman. They're heavy, their battery life is short, and they don't move in synchrony with the user. This last point is maybe the most important of the three.

Here's the deal. You don't want to spend your energy fighting with your fighting suit. But that's been a problem. In many cases, soldiers wearing these suits ended up expending more energy, rather than less (http://www.sciencemag.org/news/2015/10/feature-can-we-build-iron-man-suit-gives-soldiers-robotic-boost).

Why? Because the suit doesn't match its movements precisely with the wearer's movements. The simple act of walking (along with other simple acts we take for granted) requires a lot of computation.

Human walking is very efficient, in part because you aren't working all the time. Your legs have a pendulum-like motion. Your muscles aren't pushing the whole time your leg is moving. It swings forward and your muscles act at just the right time to provide pushes that keep the motion going.

The timing of these pushes is crucial. Think about what you do when you push a child on a swing (another pendulum). A series of small pushes can make the child swing higher—but you have to deliver those pushes at just the right time. If the timing of the robotic push isn't precisely coordinated with the effort of your muscles, the suit makes it harder to walk, rather than easier.

Then there's the question of delays in the system. Suppose you push a button in the suit to lift an arm. There's a delay between your button push and the suit response. So you push the button longer and harder—and the suit moves farther than you want. So you pull back—and that takes you too far back. The result is an oscillation, like the rough ride you get when a new driver is learning to operate a standard transmission car.

In that situation, the suit ends up fighting with you—and you're likely to lose that fight. It is, after all a "power suit."

You, the wearer, are the central processing unit of the suit. But viewed from one perspective, you are also the weakest part of the system, if the system is an armored, "Ironman" suit. The suit is tough as nails, but you are squishy and soft.

That leads to some problems. You reach up to cover your mouth when you sneeze and you slap yourself silly with your super-powered arm. You move in a way that makes the suit collide with itself—and you're in for major damage.

And much as we love the idea of the rocket thrusters in Tony Stark's boots, we'll give them a pass. When Tony's suit accelerates from zero to sixty mph in half a second, he'd feel a five-g force. His body would weigh about half a ton. If you want to know what that feels like, ask four friends to climb up on your shoulders. The suit can handle the stress, but can Tony's knees and ankles?

Fortunately, there are options other than the heavy, high-powered Ironman suit. There are labs working on suits that look nothing like Ironman's suit or Ripley's power loader.

Conor Walsh and his colleagues at the Harvard Biodesign Lab started their design of an exoskeleton by analyzing the biomechanics and physiology of human walking. They looked at how carrying heavy loads changes the biomechanics of walking.

In addition to engineers, roboticists, and biomechanists, Walsh's team includes functional apparel designers. Instead of armor, the group opted for fabric. This is soft technology—so flexible that users can wear the suit under their clothes.

The resulting exosuit works in parallel with the wearer's muscles and tendons. It applies small amounts of assistance to the muscles and tendons just when they need it. Batteries and motors are worn at the waist, and cables transmit forces to the joints.

To make all this work, the suit has soft sensors that detect the stretch and movement of a muscle. They're silicone sensors with channels filled with a conductive liquid. When your muscle stretches, so does the silicone sensor. As the silicone stretches, the resistance of the liquid to the transmission of electricity changes—and that communicates the change in the muscle.

This shift in approach seems to be paying off in efficiency. The soft exosuit has been shown to reduce the wearer's energy expenditure.

Roam Robotics, a spinoff of San Francisco-based Otherlabs, is developing air-powered soft exosuits. Tim Swift, the CEO, talks of the need for fundamental changes in the way we make and evaluate exoskeletons. His group is working to reduce weight and cost of exoskeletons without sacrificing capabilities. That's essential to making robots that are affordable and practical enough for everyday life. Swift compares a traditionally made exoskeleton arm—weighing fifteen pounds and costing $20,000—with a soft exoskeleton arm that weighs just one pound and costs twenty dollars in materials.

Forget Ironman and those super Heinlein soldiers. We're rooting for a different future: a cuddly exosuit that will help us with a nudge when we need it.
 

Paul Doherty works at The Exploratorium, San Francisco's museum of science, art, and human perception—where science and science fiction meet. For more on Paul's work and his latest adventures, visit www.exo.net/~pauld. Pat Murphy is a science educator, a science fiction writer, and occasionally a troublemaker. She works at Mystery Science, developing hands-on lessons for elementary school. You can learn more about what she's up to at www.brazenhussies.net/Murphy.