For at least eight years, DARPA has been funding R&D with the aim of building a better prosthetic arm, the Modular Prosthetic Limb (MPL). The primary objective is to advance the state of the art in prosthetics, making them more lifelike with more capabilities and more intuitive to control by amputees. Then, if all goes well, that R&D will be leveraged into both artificial arms and legs for wounded soldiers. The research results could also be used in other areas such as robotics.
It’s an ambitious project with some far-reaching goals. For example, one goal is to have an arm/hand device that can be controlled by the amputee’s thoughts. The project has made great strides, thanks to the concerted efforts of hundreds of scientists and engineers spread across 30 colleges and research labs, and millions of dollars in funding. Here’s a look at what they’ve been doing.
Power One of the many challenges in building the MPL was deciding on a power source. Initial estimates indicated it would need 50 W-hr for one day’s activity, and the couldn’t weigh more than 0.75 lb. Researchers explored several options. One, gas-powered generators, were too noisy and emitted noxious fumes. Another alternative, controlled chemical reactions — such as catalytically breaking down hydrogen peroxide to create gases that would spin small generators — was deemed too dangerous.
The team quickly settled on batteries largely based on the fact that the MPL’s sensors and motors would all need electricity, and batteries provide it without extra equipment such as generators or combustion chambers.
“Today we are using lithium-polymer batteries,” says Project Manager for MPL Development Matthew Johannes at Johns Hopkins University’s Applied Physics Lab (JHU APL). “We use them for their charge/discharge performance and power density. Currently, the batteries are in a standard configuration, but in next-generation designs, they could be custom shaped to make better use of the available space. As the design stands now, we have almost the entire forearm empty and available for batteries.”
Lithium-polymer batteries are the power choice of several prosthetic companies, including RSLSteeper in the U.