Rocket Powered Prosthetic Feet May Outrun Nature’s Own Best
Baku, November 29 (AZERTAC). Vanderbilt University scientists are developing an arm prosthesis that is powered by a miniaturized rocket engine. The advantage is stronger action of the artificial muscles, faster movement, and no need for batteries - now we’re cooking with gas!
It was the poor power-to-weight ratio of batteries that drove Goldfarb [Michael Goldfarb, Professor of Mechanical Engineering at Vanderbilt] to look for alternatives in 2000 while he was working on a previous exoskeleton project for DARPA. He decided to miniaturize the monopropellant rocket motor system that is used for maneuvering in orbit by the space shuttle. His adaptation impressed the Johns Hopkins researchers, so they offered him $2.7 million in research funding to apply this approach to the development of a prosthetic arm.
Goldfarb’s power source is about the size of a pencil and contains a special catalyst that causes hydrogen peroxide to burn. When this compound burns, it produces pure steam. The steam is used to open and close a series of valves. The valves are connected to the spring-loaded joints of the prosthesis by belts made of a special monofilament used in appliance handles and aircraft parts. A small sealed canister of hydrogen peroxide that easily fits in the upper arm can provide enough energy to power the device for 18 hours of normal activity.
The first prototype, which took a year to develop, was powered by “cold gas”: compressed nitrogen. It allowed the researchers to test the fundamental design and to address the basic problems of control, leakage and noise. The team was happy to discover that they could solve all of the basic problems by designing the valves with the highest precision possible, with clearances of 50 millionths of an inch.
“There are only a handful of machinists who can make valves with this precision. We found one and asked him to make them with the highest precision possible, which is actually higher than he can measure,” says Goldfarb. “Normally in projects like this the surprises are unpleasant, but this was a pleasant one. The valves didn’t leak, click or hiss!”
After getting the arm working with cold gas, the engineers tore it down and rebuilt it to operate on “hot gas” - steam that is heated to 450 degrees Fahrenheit by the hydrogen peroxide reaction.
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