US Army's AGRO Lands on Its Wheels Like a Motorized, Four-Wheel-Drive Militarized Cat
Like its four-footed inspiration, AGRO spins in mid-air to orient itself within half a second of release and land wheels-down.
Cats may always land on their feet, but not so robots — at least, unless you're talking about the US Army's Agile Ground Robot AGRO, which will always gain its footing within half a second of being released.
"This is the first documented use of independently steerable wheels to both drive on the ground and achieve aerial attitude control when thrown," the research team explains of its efforts in a paper presented at the IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS '20). "Inspired by a cat's self-righting reflex, this capability was developed to allow emergency response personnel to rapidly deploy AGRO by throwing it over walls and fences or through windows without the risk of it landing upside down. It also allows AGRO to drive off of ledges and ensure it lands on all four wheels."
"We have demonstrated a successful thrown deployment of AGRO. A novel parametrization and singularity analysis of 4WIDS [four-wheeled independent drive and steering] kinematics reveals independent yaw authority with simultaneous adjustment of the ratio between roll and pitch authority. Simple PD controllers allow for stabilization of roll, pitch, and yaw. These controllers were tested in a simulation using derived dynamic equations of motion, then implemented on the AGRO prototype."
The system has proven its worth in prototype, powered by an Arm Mbed Nucleo F446RE microcontroller board: AGRO was dropped from a height of 33.5in and at angle of 16 degrees roll and -23 degrees pitch. Normally this would mean an inability to drive off — but with the controller system enabled AGRO used its four independently-controllable wheels to create reaction torque and stabilize its orientation in around 400 milliseconds."
Speaking to IEEE Spectrum, project lead Daniel J. Gonzalez claims that AGRO is capable of even more impressive feats than demonstrated for the paper — including the ability to recover from any orientation, given enough flight time and providing its release rotation speed is under 66 revolutions per minute - after which the in-wheel hub motors can no longer spin fast enough to counteract the motion.
The paper is available on arXiv.org under open-access terms.