Similarity of legs, wheels, tracks suggests target for energy-efficient robots
The Legged Locomotion and Movement Adaptation, or LLAMA, is an autonomous quadruped mobility research platform system patterned after a working dog and similar animals. Army researchers designed it to work alongside Soldiers, lighten physical workloads, and increase mobility, protection and lethality. Photo credit: U.S. Army
A new formula from Army scientists is leading to new insights on how to build an energy-efficient legged teammate for dismounted warfighters.
In a recent peer-reviewed PLOSE One paper, the U.S. Army Combat Capabilities Development Command, known as DEVCOM, Army Research Laboratory’s Drs. Alexander Kott, Sean Gart and Jason Pusey offer new insights on building autonomous military robotic legged platforms to operate as efficiently as any other ground mobile systems.
Its use could lead to potentially important changes to Army vehicle development. Scientists said they may not know exactly why legged, wheeled and tracked systems fit the same curve yet, but they are convinced their findings drive further inquiry.
Inspired by a 1980s formula that shows relationships between the mass, speed and power expenditure of animals, the team developed a new formula that applied to a very broad range of legged, wheeled and tracked systems – such as motor vehicles and ground robots.
Although much of the data has been available for 30 years, this team believes they are the first to actually assemble it and study the relationships that emerge from this data.
“In the world of unmanned combat aerial vehicle and intelligent munitions, there is a growing role for dismounted infantry that can advance, often for multiple days, and attack in the most cluttered terrain such as mountains, dense forests and urban environments,” said Kott, chief scientist.“
As a starting point, the team investigated a scaling formula proposed in the 1980s for estimating the mechanical power expended by an animal of a given mass to move at a given speed, and compared this to a range of artificial mechanical systems varying in size, weight and power that are autonomous or driven by humans.
They studied wide ranges of sizes and morphologies within a data set that combined systems that included for example a 17th century British canon, the Ford Model T, the M1 Abrams tank and an ACELA train.
The team found a similar, consistent relationship does in fact apply also to ground-mobile systems including vehicles of different types over a broad range of their masses.
Kott said these findings suggest that human-made legged platforms should be as efficient as wheeled and tracked platforms.
Gart said their research is relevant to designing ground mobile systems because it helps designers determine tradeoffs among power, speed and mass for future terrestrial robots for defense applications.
One Army goal is to develop new types of autonomous, or partly autonomous, ground vehicle to deliver supplies to Soldiers in challenging terrains, he said.
“To haul supplies, it must be able to carry a certain weight, or mass, at a certain time, or speed,” Gart said.
“The Army must develop feasible yet ambitious targets for tradeoffs among the power, speed, and mass of future terrestrial robots,” Kott said.
The formula developed in this paper gives such a target and could enable the Army to make predictions of future performance of ground platforms such as legged robots given design constraints like vehicle and motor weight and desired speed, he said.