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New Gears Can Withstand Impact, Freezing Temperatures During Lunar Missions

BMGG

Andrew Kennett (left) watches as Dominic Aldi (right) uses liquid nitrogen to cool a motor integrated bulk metallic glass gearbox prior to shock testing it. The motor and gearbox are inside the frosty metal “bucket” that contains the liquid nitrogen. The tooling, including the “bucket” is designed to be mounted both vertically (shown) and horizontally on the cube for testing the motor and gearbox in three orientations. Credits: NASA/JPL-Caltech

BMGG

The motor and gearbox are mounted for testing in one of two horizontal orientations. Frost forms on the surface of the “bucket” when liquid nitrogen is used to cool the hardware to the test temperature of -279 degrees Fahrenheit (-173 degrees Celsius). Credits: NASA/JPL-Caltech

BMGG

The shock for the test is generated by launching a steel mass (one of the round cylinders in the lower left of the image) into the bottom of the long steel beam. The large clamps set the length of the beam that can “ring” from the impact. By changing the clamp position the profile of the shock can be tuned, hence the name “tunable beam.” The large cube mounted to the beam simplifies mounting of hardware for testing. The shock event is captured using an accelerometer mounted at the hardware.
Credits: NASA/JPL-Caltech

Many exploration destinations in our solar system are frigid and require hardware that can withstand the extreme cold. During NASA’s Artemis missions, temperatures at the Moon’s South Pole will drop drastically during the lunar night. Farther into the solar system, on Jupiter’s moon Europa, temperatures never rise above -260 degrees Fahrenheit (-162 degrees Celsius) at the equator.

One NASA project is developing special gears that can withstand the extreme temperatures experienced during missions to the Moon and beyond. Typically, in extremely low temperatures, gears – and the housing in which they’re encased, called a gearbox – are heated. After heating, a lubricant helps the gears function correctly and prevents the steel alloys from becoming brittle and, eventually, breaking. NASA’s Bulk Metallic Glass Gears (BMGG) project team is creating material made of “metallic glass” for gearboxes that can function in and survive extreme cold environments without heating, which requires energy. Operations in cold and dim or dark environments are currently limited due to the amount of available power on a rover or lander.

The BMGG unheated gearboxes will reduce the overall power needed for a rover or lander’s operations, such as pointing antennas and cameras, moving robotic arms, handling and analyzing samples, and mobility (for a rover). The power saved with the BMGG gearbox could extend a mission or allow for more instruments.

The team recently tested the gears at NASA’s Jet Propulsion Laboratory in Southern California. At JPL’s Environmental Test Laboratory, engineers mounted the motor and gearbox on a tunable beam designed to measure the response an item has to a shock, or forceful impact. Team members then used liquid nitrogen to cool the gears down to roughly to -279 degrees Fahrenheit (-173 degrees Celsius). Next, they fired a cylindrical steel projectile at the beam to simulate a “shock event.” Shock testing is used to ensure spacecraft hardware will not break during events that cause a sudden jolt, such as the release of an antenna or what a spacecraft experiences during entry, descent, and landing. The test simulated how the bulk metallic glass gears might behave when collecting a regolith sample during the lunar night – which spans roughly 14 days on Earth – or deploying a science instrument on an ocean world in our solar system.

“Before NASA sends hardware like gearboxes, particularly those made with new materials, to extremely cold environments, we want to make sure they will not be damaged by the stressful events that occur during the life of a mission,” said Peter Dillon, BMGG project manager at JPL. “This shock testing simulates the stresses of entry, descent, and landing, and potential surface operations.”

Before each shock test, a team member poured liquid nitrogen over the motor and gearbox contained in a “bucket.” Liquid nitrogen, which boils at -320 degrees Fahrenheit (-196 degrees Celsius), brought the gearbox’s temperature below -279 degrees Fahrenheit (-173 degrees Celsius). The liquid nitrogen drained and, within a few seconds, a steel impactor fired at a steel beam on which the motor and gearbox were mounted. The team then ran the motor to drive the gearbox to determine whether or not the shock event had damaged the gearbox and its motor. The team monitored the electrical current required to run the motor and listened for any irregular sounds that indicated damage. The motor and gearbox were shock tested twice in three different orientations. Each test demonstrated that the gears could withstand a “shock event” at a temperature as low as -279 degrees Fahrenheit (-173 degrees Celsius).

“This is an exciting event as it demonstrates both the mechanical resilience of the bulk metallic glass alloy and the design of the gearbox,” Dillon said. “These gears could help enable potential operations during the lunar night, in permanently shadowed lunar craters, in polar regions on the Moon, and on ocean worlds.”

The BMGG team will perform additional cold temperature testing next year to qualify the gears for use in future NASA missions.

Learn more about the BMGG project:

https://www.nasa.gov/directorates/spacetech/game_changing_development/projects/BMGG/

 

Hillary Smith
NASA Langley Research Center
hillary.smith@nasa.gov
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Metallic Glass Gears Make for Graceful Robots

Metallic Glass Gears

Metallic Glass Gears Make for Graceful Robots Space Gears Harmonic drive Bulk metallic glass, a metal alloy, doesn’t get brittle in extreme cold. That makes the material perfect for robotics operated in space or on icy planets.Image Credit: NASA/JPL-Caltech

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.

What makes these gears perfect for space?

Among their attractive qualities, BMGs have low melting temperatures. That allows parts to be cast using injection-molding technology, similar to what’s used in the plastics industry, but with much higher strength and wear-resistance. BMGs also don’t get brittle in extreme cold, a factor which can lead to a gear’s teeth fracturing. This last quality makes the material particularly useful for the kinds of robotics done at JPL.

Hofmann said that gears made from BMGs can “run cold and dry”: initial testing has demonstrated strong torque and smooth turning without lubricant, even at -328 degrees Fahrenheit (-200 degrees Celsius). For robots sent to frozen landscapes, that can be a power-saving advantage. NASA’s Mars Curiosity rover, for example, expends energy heating up grease lubricant every time it needs to move.

“Being able to operate gears at the low temperature of icy moons, like Europa, is a potential game changer for scientists,” said R. Peter Dillon, a technologist and program manager in JPL’s Materials Development and Manufacturing Technology Group. “Power no longer needs to be siphoned away from the science instruments for heating gearbox lubricant, which preserves precious battery power.”

Gears that turn smoothly while cutting costs

The second paper led by Hofmann looked at how BMGs could lower the cost of manufacturing strain wave gears. This type of gear, which includes a metal ring that flexes as the gear spins, is tricky to mass produce and ubiquitous in expensive robots.

Not only can BMGs allow these gears to perform at low temperatures, but they can also be manufactured at a fraction of the cost of their steel versions without sacrificing performance. This is potentially game changing for reducing the cost of robots that use strain wave gears, since they are often their most expensive part.

“Mass producing strain wave gears using BMGs may have a major impact on the consumer robotics market,” Hofmann said. “This is especially true for humanoid robots, where gears in the joints can be very expensive but are required to prevent shaking arms. The performance at low temperatures for JPL spacecraft and rovers seems to be a happy added benefit.”

The paper published by Advanced Engineering Materials looked at designing and testing BMG gears for planetary gearboxes. It included collaborators at Caltech and UC San Diego. The paper published in Scientific Reports examines how BMGs can be used to reduce the cost of strainwave gears. It also included Caltech collaborators.

The Bulk Metallic Glass Gears project is funded by NASA’s Space Technology Mission Directorate’s Game Changing Development Program, which investigates ideas and approaches that could solve significant technological problems and revo¬lutionize future space endeavors.

Caltech manages JPL for NASA.

For more information about Hofmann’s research, visit:

http://scienceandtechnology.jpl.nasa.gov/metallurgy-facility

 

News Media Contact

Andrew Good
Jet Propulsion Laboratory, Pasadena, Calif.
818-393-2433
andrew.c.good@jpl.nasa.gov

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*Source: NASA.gov

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