An unmanned aerial vehicle (UAV) system is disclosed. The UAV system includes a chassis, a plurality of propeller assemblies configured to provide vertical take-off and landing (VTOL) for the chassis with propulsion in 6 degrees of freedom including along a cartesian coordinate system (X, Y, Z) and provide yaw, pitch, and roll, the plurality of propeller assemblies are selected from the group consisting of (i) two fixed propeller assemblies and a tiltable propeller assembly, and (ii) four fixed propeller assemblies, a boom having a boom propeller assembly, configured to selectively provide positive and negative rectilinear thrust vectors, and an end-effector coupled to a distal end of the boom, the end-effector having a force sensor configured to provide contact force between the end-effector and an object.