Sorry, but some may be unaware of current off-the-shelf drone technologies available to the public. I could stand at the foot of this ladder and fly a first person perspective quad copter drone right up into the cave with no problem at all. The ladder is very wide, and the drones are not that wide. Many such drones are less wide than human shoulders, and could navigate through tunnels at will. Of course you couldn't travel down long sections of tunnels without signal loss, which is why some people use battery powered signal repeaters that the drones drop off every so often to maintain their flight and video links. And I don't use 3g or wifi, I use other frequencies that deal with obstacles better.
But again, I am not promoting the idea that such drones should be employed to explore this cave.
C'mon, folks, don't fall for this obvious ploy. There are many other areas where you could put such drone technology to better use than to think there is something in this cave worthy of your efforts. And all it would take is a confused bat flying into one of your props to crash your drone in a very hard to reach place. Or even bat crap falling into one of them from above. You won't catch me trying to use a drone to explore this cave, I have better ways to waste my time.