Tiny ball magnets implanted in muscles could provide much better control over prosthetics.

Magnets Could Give Prosthetic Control A Leg Up

Today, prostheses and exoskeletons are controlled using electromyography. In other words, by recording the electrical activity in muscles as they contract. It’s neither intuitive nor human-like, and it really only shows the brain’s intent, not the reality of what the muscle is doing.

Researchers at MIT’s Media Lab have figured out a way to use magnets for much more precise control, and they’re calling it magnetomicrometry (MM). By implanting pairs of tiny ball magnets and tracking their movement with magnetic sensors, each muscle can be measured individually and far more accurately than with electromyography.

After embedding pairs of 3mm diameter ball magnets into the calves of turkeys, the researchers were able to detect muscle movement in three milliseconds, and to the precision of thirty-seven microns, which is about the width of a human hair. They hope to try MM on humans within the next couple of years. It would be a great solution overall if it works out, because compared with the electromyography method, MM is cheaper, less invasive, and potentially permanent. Couple MM with a new type of amputation surgery called AMI that provides a fuller range of motion, less pain overall, and finer control of prosthetics, and the future of prostheses and rehabilitation looks really exciting. Be sure to check out the video after the break.

There’s more than one way to control prostheses, such as deep learning and somatosensory stimulation.

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Deep Learning Enables Intuitive Prosthetic Control

Prosthetic limbs have been slow to evolve from simple motionless replicas of human body parts to moving, active devices. A major part of this is that controlling the many joints of a prosthetic is no easy task. However, researchers have worked to simplify this task, by capturing nerve signals and allowing deep learning routines to figure the rest out.

The prosthetic arm under test actually carries a NVIDIA Jetson Nano onboard to run the AI nerve signal decoder algorithm.

Reported in a pre-published paper, researchers used implanted electrodes to capture signals from the median and ulnar nerves in the forearm of Shawn Findley, who had lost a hand to a machine shop accident 17 years prior. An AI decoder was then trained to decipher signals from the electrodes using an NVIDIA Titan X GPU.

With this done, the decoder model could then be run on a significantly more lightweight system consisting of an NVIDIA Jetson Nano, which is small enough to mount on a prosthetic itself. This allowed Findley to control a prosthetic hand by thought, without needing to be attached to any external equipment. The system also allowed for intuitive control of Far Cry 5, which sounds like a fun time as well.

The research is exciting, and yet another step towards full-function prosthetics becoming a reality. The key to the technology is that models can be trained on powerful hardware, but run on much lower-end single-board computers, avoiding the need for prosthetic users to carry around bulky hardware to make the nerve interface work. If it can be combined with a non-invasive nerve interface, expect this technology to explode in use around the world.

[Thanks to Brian Caulfield for the tip!]

Console Controller Mod Gets Amputee Back In The Game

No matter how it happens, losing one or more fingers is going to change one’s life in thousands of ways. We’re a manipulative species, very much accustomed to interacting with the world through the amazing appendages at the ends of our arms. Finding ways around the problems that result from amputations is serious business, of course, even when it’s just modifying a game console controller for use with a prosthetic hand.

We’ve gotten to know [Ian Davis] quite well around these parts, at least from his videos and Instagram posts. [Ian]’s hard to miss — he’s in the “Missing Parts Club” as he puts it, consisting of those who’ve lost all or part of a limb, which he has addressed through his completely mechanical partial-hand prosthetic. As amazing as the mechanical linkages of that prosthetic are, he hasn’t regained full function, at least not to the degree required to fully use a modern game console controller, so he put a couple of servos and a Trinket to work to help.

An array of three buttons lies within easy reach of [Ian]’s OEM thumb. Button presses there are translated into servo movements that depress the original bumper buttons, which are especially unfriendly to his after-market anatomy. Everything rides in an SLA-printed case that’s glued atop the Playstation controller. [Ian] went through several design iterations and even played with the idea of supporting rapid fire at one point before settling on the final design shown in the video below.

It may not make him competitive again, but the system does let him get back in the game. And he’s quite open about his goal of getting his designs seen by people in a position to make them widely available to other amputees. Here’s hoping this helps.

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Plastic Prosthetics For Rubber Duckies

Will someone please think of the rubber duckies?!

For decades they’ve been reduced to a laughing stock: a caricature of waterfowl. Left without a leg to stand on, their only option is to float around in the tub. And they don’t even do that well, lacking the feet that Mother Nature gave them, they capsize when confronted with the slightest ripple. But no more!

Arise!

Due to the wonders of 3D printing, and painstaking design work by [Jan] from the Rubber Ducky Research Center, now you can print your own rubber ducky feet. We have the technology! Your ducks are no longer constrained to a life in the tub, but can roam free as nature intended. The video (embedded below) will certainly tug at your heartstrings.

OK, it’s a quick print and it made my son laugh.

The base and legs probably don’t fit your duck as-is, but it’s a simple matter to scale them up or down while slicing. (Picture me with calipers on the underside of a rubber ducky.) The legs were a tight press-fit into the body, so you might consider slimming them down a tiny bit when doing the scaling, but this probably depends on your printer tolerances.

It looks snazzy in gold-fleck PETG, and would probably work equally well for some more elaborate rubber duckies as well.

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Hackaday Links: July 5, 2020

Remember all the hubbub over Betelgeuse back in February? For that matter, do you even remember February? If you do, you might recall that the red giant in Orion was steadily dimming, which some took as a portent of an impending supernova. That obviously didn’t happen, but we now seem to have an explanation for the periodic dimming: an enormous dark spot on the star. “Enormous” doesn’t begin to describe this thing, which covers 70% of the face of a star that would extend past Jupiter if it replaced the sun. The dimming was originally thought to be dust being blown off the star as it goes through its death throes, but no evidence could be found for that, while direct observations in the terahertz range showed what amounted to a reduction in surface temperature caused by the enormous star spot. We just think it’s incredibly cool that Betelgeuse is so big that we can actually observe it as a disk rather than a pinpoint of light. At least for now.

F-15c cockpit
F-15a cockpit

If you think you’ve seen some challenging user interfaces, wait till you get a load of the cockpit of an F-15C Eagle. As part of a new series on human interfaces, Ars Technica invited Col. Andrea Themely (USAF-ret.) to give a tour of the fighter she has over 1,100 hours on. Bearing in mind that the Eagle entered service in 1976 and has been continually updated with the latest avionics — compare the video with the steam gauges of the cockpit of an F-15A — its cockpit is still a pretty busy place. As much as possible has been done to reduce pilot load, with controls being grouped by function and the use of color-coding — don’t touch the yellow and black stuff! — and the use of tactile feedback. It’s a fascinating deep dive into a workplace that few of us ever get to see, and we’re looking forward to the rest of the series.

Sad news from Seattle, where the Living Computers: Museum + Labs is closing up shop. The announcement only says they’re closing “for now”, so there’s at least some hope that the museum will be back once the COVID-19 downturn has run its course. We hope they do bounce back; it really was a great museum with a lot of amazing hardware on display. The Vintage Computer Festival PNW was held there in its inaugural year, an event we covered and had high hopes for in the future. We hope for the best for these educational and cultural institutions, but we can’t help but fear a little for their future.

So you suffer a partial amputation of your left hand, leaving you with only your thumb and your palm. That raises an interesting conundrum: you haven’t lost enough to replace the hand with a prosthetic one, but you still don’t have any fingers. That appears to be what happened to Ian Davis, and so he built his own partial prosthetic to replace his fingers. There’s not much backstory on his YouTube channel, but from what we can gather he has gone through several designs, most of which are myomechanical rather than myoelectric. Through a series of complex linkages, he’s able to control not only the opening and closing of the fingers, but also to splay them apart. It’s all in the wrist, as it were — his input gestures all come from flexing and extending his hand relative to his forearm, where the prosthesis is anchored. This results in a pretty powerful grip — much stronger than a myoelectric hand in a head-to-head test. And the coolness factor of his work is just off the scale. We’re looking forward to more from Ian, and hopefully enough background information for a full story on what he has accomplished.

FitSocket Is A Portal To Better Prostheses

Traditionally, sockets for prostheses are created by making a plaster cast of the limb being fitted, and are then sculpted in carbon fiber. It’s an expensive and time-consuming process, and what is supposed to be a customized socket often turns out to be an uncomfortable disappointment. Though prosthetists design these sockets specifically to take pressure off of the more rigid areas of tissue, this usually ends up putting more pressure on the softer areas, causing pain and discomfort.

An MIT team led by [Arthur Preton] wants to make prosthesis sockets more comfortable and better customized. They created FitSocket, a machine that assesses the rigidity of limb tissue. You can see it in motion after the break.

FitSocket is essentially a ring of 14 actuators that gently prod the limb and test how much pressure it takes to push in the tissue. By repeating this process over the entire limb, [Preton] can create a map that shows the varying degrees of stiffness or softness in the tissue.

We love to see advancements in prostheses. Here’s an electronic skin that brings feeling to artificial fingertips.

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Flex PCBs Make Force-Mapping Pressure Sensor For Amputee

What prosthetic limbs can do these days is nothing short of miraculous, and can change the life of an amputee in so many ways. But no matter what advanced sensors and actuators are added to the prosthetic, it has to interface with the wearer’s body, and that can lead to problems.

Measuring and mapping the pressure on the residual limb is the business of this flexible force-sensing matrix. The idea for a two-dimensional force map came from one of [chris.coulson]’s classmates, an amputee who developed a single-channel pressure sensor to help him solve a painful fitting problem. [chris.coulson] was reminded of a piezoresistive yoga mat build from [Marco Reps], which we featured a while back, and figured a scaled-down version might be just the thing to map pressure points across the prosthetic interface. Rather than the expensive and tediously-applied web of copper tape [Marco] used, [chris] chose flexible PCBs to sandwich the Velostat piezoresistive material. An interface board multiplexes the 16 elements of the sensor array to a PIC which gathers and records testing data. [chris] even built a test stand with a solenoid to apply pressure to the sensor and test its frequency response to determine what sorts of measurements are possible.

We think the project is a great application for flex PCBs, and a perfect entry into our Flexible PCB Contest. You should enter too. Even though [chris] has a prototype, you don’t need one to enter: just an idea would do. Do something up on Fritzing, make a full EAGLE schematic, or just jot a block diagram down on a napkin. We want to see your ideas, and if it’s good enough you can win a flex PCB to get you started. What are you waiting for?