Although this thread is over a year old now since last exercised I thought it might worth exploring again in the light of increased media hype over multicopter UAVs, I do hate the D word!!
On the original subject of using UAVs underground. I do think that on an amateur level there are easier less expensive ways of achieving "aerial shots". Where underground dimensions allow e.g. something like Titan, then there could well be an argument for using one but Mike's dangle on a rope (with gimbal of course) would achieve the same effect. Post production would allow you to either make it rise or fall. Talking of gimbals, this is one area to which the UAV market has pushed development and seen spin offs into photography which were previously only accessible if you had big pockets and now is expanding into the video world along with electronic image stabilisation.
There are in my mind 2 main issues in using UAVs underground, control and visual perspective. If we look at control. The vast majority of out of the box hobby UAVs use GPS as the main overriding control system. Without a clear GPS signal many of the newer UAVs will not arm the motors let alone get airborne. This feature as a result of recent UAV incidents is only going to be more common, indeed I wouldn't be surprised if legislation possibly via the CAA comes into force in the near future. As ever though if you know what you are doing, currently, it can be circumvented. However as I know only too well you have to be a bloody good pilot to control a UAV in freestyle mode, especially in the limiting confines underground.
BTW just to clarify we are not talking about the small sub £60-ish quadcopters which only use gyro stabilisation not GPS.
Just in case anyone needs to know why many UAVs need GPS before they will fly. Manufacturers are not daft and in order to keep selling these things they naturally listen to all feed back. Authorities of all shades, everywhere are concerned by the blatant misuse and downright idiotic flying by some individuals. As part of the much banded "duty of care" syndrome and the potential litigation issues, manufacturers are taking steps to stop such eventualities. GPS is already onboard and therefore it is a simple step to provide firmware which can utilise GPS and prevent the UAV from starting dependant on its position. I.e. Near an international airport, sensitive military area etc. some of the earlier versions of UAVs have an override freestyle mode but I do think this will become a thing of the past.
Going back to 2 main issues. Visual perspective. Any flying in the dark or limited light brings its own unique problems. As humans we rely very much on our peripheral vision for our spatial awareness. If we were to use FPV, which would be sensible in large system areas underground, you loose to a degree your peripheral vision. When this happens especially in low light there is a tendency for the observer to pull back to try to re-establish their perspective. This phenomenon is well known especially in night flying of helicopters on take off in to the hover. It has caused many crashes in confined areas operations. If FPV goggles were to be used it would most prudent to use an observer to give the pilot extra spatial information. In fact you can get an idea of what I'm on about if you have a UAV stand by it on the ground in front of you. Then just take off vertically no other controls other than the GPS lock on, as high as you can. As the UAV rises it appears to pass over your head as you look up and you tend to want to step back. Then slowly bring the UAV down and if you have a good lock it should return to the starting position.
Having said all of the above would you really want to be underground with the sounds of a manic buzzing vehicle nearby with the potential of it unintentionally heading in your direction!!
One of the good things about all this technology is the spin off into others fields of photography. Some of you know of my kite aerial photos. Well for sometime now I've also been adapting some of the UAV technology to my kite flying. Last November I made up my first gimballed video rig, finally last weekend I managed to get the whole kit airborne and below is the resulting imagery.
https://vimeo.com/162647662 BTW if you think the video is off topic (mine related), think again. Apart from 2 quarries there are least 4 mine shafts in view. No prizes if you find them.
I rate this as a successful flight. You can see quite clearly the degree to which the gimbal stabilises the video. Actually in use I would be using the kit at lower altitudes than shown. This opens the door to more technology aloft. I already have a near infra red set up (stills and video). Now there are miniature thermal cameras along the lines of the Flir One. This, whether you use kite or UAV, opens up readily accessible survey tools for the amateur industrial archeologist.
Hopefully given a reasonable summer I am going to try and try out some of the toys!