  We present the dynamic model and control of DoubleBee, a novel hybrid
aerial-ground vehicle consisting of two propellers mounted on tilting servo
motors and two motor-driven wheels. DoubleBee exploits the high energy
efficiency of a bicopter configuration in aerial mode, and enjoys the low power
consumption of a two-wheel self-balancing robot on the ground. Furthermore, the
propeller thrusts act as additional control inputs on the ground, enabling a
novel decoupled control scheme where the attitude of the robot is controlled
using thrusts and the translational motion is realized using wheels. A
prototype of DoubleBee is constructed using commercially available components.
The power efficiency and the control performance of the robot are verified
through comprehensive experiments. Challenging tasks in indoor and outdoor
environments demonstrate the capability of DoubleBee to traverse unstructured
environments, fly over and move under barriers, and climb steep and rough
terrains.
