In order to make a better arm, Kamen first had to figure out what was wrong with the old one. Part of the reason the technology was still in "the Flintstones" was a lack of agility: a human arm has 22 degrees of freedom, not three. The Luke Arm prosthetic is agile because of the fine motor control imparted by the enormous amount of circuitry inside the arm, which enables 18 degrees of freedom. The engineers fought for space inside the arm and created workarounds when they couldn’t have the space they needed, such as using rigid-to-flex circuit boards folded into origami-like shapes inside the tiny spaces, which are connected by a dense thicket of wiring.
A sensor on the Luke hand, connected to a microprocessor, sends a signal to the tactor, and that signal changes with grip strength. When a user grips something lightly, the tactor vibrates slightly. As the user’s grip tightens, the frequency of the vibration increases. This enables Hildreth to pick up and drink out of a flimsy paper cup without crushing it, or firmly hold a heavy cordless drill without dropping it. "I can do things I haven’t done in 26 years," he says, looking at his hand. "I can peel a banana without squishing it."
Aluminium and carbon fiber. They're learning...