  The use of Micro Aerial Vehicles (MAVs) for inspection and surveillance
missions has proved to be extremely useful, however, their usability is
negatively impacted by the large power requirements and the limited operating
time. This work describes the design and development of a novel hybrid
aerial-ground vehicle, enabling multi-modal mobility and long operating time,
suitable for long-endurance inspection and monitoring applications. The design
consists of a MAV with two tiltable axles and four independent passive wheels,
allowing it to fly, approach, land and move on flat and inclined surfaces,
while using the same set of actuators for all modes of locomotion. In
comparison to existing multi-modal designs with passive wheels, the proposed
design enables a higher ground locomotion efficiency, provides a higher payload
capacity, and presents one of the lowest mass increases due to the ground
actuation mechanism. The vehicle's performance is evaluated through a series of
real experiments, demonstrating its flying, ground locomotion and wall-climbing
capabilities, and the energy consumption for all modes of locomotion is
evaluated.
