Throw a baseball, and you might say it’s all in the wrist.
For robots, it’s all in the gears.
Gears are essential for precision robotics. They allow limbs to turn smoothly and stop on command; low-quality gears cause limbs to jerk or shake. If you’re designing a robot to scoop samples or grip a ledge, the kind of gears you’ll need won’t come from a hardware store.
At NASA’s Jet Propulsion Laboratory in Pasadena, California, technologist Douglas Hofmann and his collaborators are building a better gear. Hofmann is the lead author of two recent papers on gears made from bulk metallic glass (BMG), a specially crafted alloy with properties that make it ideal for robotics.
“Although BMGs have been explored for a long time, understanding how to design and implement them into structural hardware has proven elusive,” said Hofmann. “Our team of researchers and engineers at JPL, in collaboration with groups at Caltech and UC San Diego, have finally put BMGs through the necessary testing to demonstrate their potential benefits for NASA spacecraft. These materials may be able to offer us solutions for mobility in harsh environments, like on Jupiter’s moon Europa.”
Recipe for the perfect gear
How can this mystery material be both a metal and a glass? The secret is in its atomic structure. Metals have an organized, crystalline arrangement. But if you heat them up into a liquid, they melt and the atoms become randomized. Cool them rapidly enough –about 1,832 degrees Fahrenheit (1,000 degrees Celsius) per second — and you can trap their non-crystalline, “liquid” form in place.
This produces a random arrangement of atoms with an amorphous, or non-crystalline microstructure. That structure gives these materials their common names: “amorphous metals,” or metallic glass.
By virtue of being cooled so rapidly, the material is technically a glass. It can flow easily and be blow-molded when heated, just like windowpane glass. When this glassy material is produced in parts greater than about .04 inches (1 millimeter), it’s called “bulk” metallic glass, or BMG.
Metallic glasses were originally developed at Caltech in Pasadena, California, in 1960. Since then, they’ve been used to manufacture everything from cellphones to golf clubs…