  Unmanned aerial vehicles are rapidly evolving within the field of robotics.
However, their performance is often limited by payload capacity, operational
time, and robustness to impact and collision. These limitations of aerial
vehicles become more acute for missions in challenging environments such as
subterranean structures which may require extended autonomous operation in
confined spaces. While software solutions for aerial robots are developing
rapidly, improvements to hardware are critical to applying advanced planners
and algorithms in large and dangerous environments where the short range and
high susceptibility to collisions of most modern aerial robots make
applications in realistic subterranean missions infeasible. To provide such
hardware capabilities, one needs to design and implement a hardware solution
that takes into the account the Size, Weight, and Power (SWaP) constraints.
This work focuses on providing a robust and versatile hybrid platform that
improves payload capacity, operation time, endurance, and versatility. The
Bi-modal Aerial and Terrestrial hybrid vehicle (BAXTER) is a solution that
provides two modes of operation, aerial and terrestrial. BAXTER employs two
novel hardware mechanisms: the M-Suspension and the Decoupled Transmission
which together provide resilience during landing and crashes and efficient
terrestrial operation. Extensive flight tests were conducted to characterize
the vehicle's capabilities, including robustness and endurance. Additionally,
we propose Agile Mode Transfer (AMT), a transition from aerial to terrestrial
operation that seeks to minimize impulses during impact to the ground which is
a quick and simple transition process that exploits BAXTER's resilience to
impact.
