  This paper develops and compares two motion planning algorithms for a
tethered UAV with and without the possibility of the tether contacting the
confined and cluttered environment. Tethered aerial vehicles have been studied
due to their advantages such as power duration, stability, and safety. However,
the disadvantages brought in by the extra tether have not been well
investigated by the robotic locomotion community, especially when the tethered
agent is locomoting in a non-free space occupied with obstacles. In this work,
we propose two motion planning frameworks that (1) reduce the reachable
configuration space by taking into account the tether and (2) deliberately plan
(and relax) the contact point(s) of the tether with the environment and enable
an equivalent reachable configuration space as the non-tethered counterpart
would have. Both methods are tested on a physical robot, Fotokite Pro. With our
approaches, tethered aerial vehicles could find their applications in confined
and cluttered environments with obstacles as opposed to ideal free space, while
still maintaining the advantages from the usage of a tether. The motion
planning strategies are particularly suitable for marsupial heterogeneous
robotic teams, such as visual servoing/assisting for another mobile,
tele-operated primary robot.
