  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.
