Mini Rocket Propulsion For Bionic Arm

Life sometimes imitates cartoons and TV shows. Shades of the Bionic Woman and the Six Million Dollar Man:

Combine a mechanical arm with a miniature rocket motor: The result is a prosthetic device that is the closest thing yet to a bionic arm.

A prototype of this radical design has been successfully developed and tested by a team of mechanical engineers at Vanderbilt University as part of a $30 million federal program to develop advanced prosthetic devices.

“Our design does not have superhuman strength or capability, but it is closer in terms of function and power to a human arm than any previous prosthetic device that is self-powered and weighs about the same as a natural arm,” says Michael Goldfarb, the professor of mechanical engineering who is leading the effort.

The prototype can lift (curl) about 20 to 25 pounds – three to four times more than current commercial arms – and can do so three to four times faster. “That means it has about 10 times as much power as other arms despite the fact that the design hasn’t been optimized yet for strength or power,” he says.

Goldfarb decided on the miniaturized rocket propellant approach because batteries can't provide enough power to make strong prosthetic arms.

At a certain point, the weight of the batteries required to provide the energy to operate the arm for a reasonable period becomes a problem. It was the poor power-to-weight ratio of the batteries that drove Goldfarb 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 by the space shuttle for maneuvering in orbit. 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 hydrogen peroxide 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 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.

I'm expecting nanotubes designed to work more like muscles will eventually displace rockets and electric motors from arms. Though a rocket arm could some day support a rocket punch that would make a rocket-propelled fist and forearm pretty attractive to some.

By Randall Parker at 2007 August 20 11:00 PM  Cyborg Tech | TrackBack