Dynamics and Aerial Attitude Control for Rapid Emergency Deployment of the Agile Ground Robot AGRO

TL;DR

This paper introduces AGRO, a four-wheeled robot capable of aerial attitude control using wheel reaction torques, enabling rapid deployment and safe landing after being thrown over obstacles in emergency scenarios.

Contribution

It presents the first use of independently steerable wheels for both ground mobility and aerial attitude control in a thrown robot, with a novel kinematic analysis and stabilization method.

Findings

AGRO can stabilize its orientation within 402 ms after being thrown.

Successful demonstration of AGRO's deployment and landing stability.

Simulation and real-world experiments confirm effectiveness of control approach.

Abstract

In this work we present a Four-Wheeled Independent Drive and Steering (4WIDS) robot named AGRO and a method of controlling its orientation while airborne using wheel reaction torques. This is the first documented use of independently steerable wheels to both drive on the ground and achieve aerial attitude control when thrown. 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 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. An experiment comparing a controlled and non-controlled fall was conducted in which AGRO was dropped from a height of 0.85 m with an initial roll and pitch angle of 16 degrees and -23 degrees respectively. With the controller enabled, AGRO can use the reaction torque from its wheels to stabilize its orientation within 402 milliseconds.