A propellable apparatus comprises one or more rotatable membranes. The rotatable membranes include an inner surface at least partially defining an encircled region and a continuous outer surface that turns outward to engage a cavity or lumen wall, for example, and turns inward to at least partially encompass a central region defining a longitudinal path. The membranes are powerable to provide movement relative to the cavity or lumen wall. The apparatus further comprises an inflatable and deflatable support structure, configured to bias the outer surface of the membranes outward to engage the cavity or lumen wall at a first outer diameter, and be deformable inward in response to a compressive force or operator command to provide a second outer diameter that is less than the first outer diameter. In some examples, the rotatable membranes include belt-like membranes, and the inflatable and deflatable support structure includes at least one impermeable bladder.
