What do we know so far: Hanging a bat detector from a single pivot point with string doesn't work, have a look at the blog post here for what happens.
Next up the bat detector was attached to each of the four quadcopter arms using string at a distance of 3m.
There's no video of this unfortunately but it didn't work. There was still huge oscillation with the load which would have lead to a crash if it had continued.
The second option that was tried was a solid rod which could pivot with the pitch of the quadcopter. The idea here was to try and fly the quadcopter with pitch and yaw only. Here's a few photos of the design:
The pivot is made from meccano and a few bolts from B&Q. The rod was meant for fishing and I think it's a glass/carbon fibre composite.
Here's what happened when it was flown:
So this didn't work either. It's not particularly clear from the video but the fact that there's almost no roll component to the flight makes the quad very difficult to control. Once a load was added to the extention of the rod it would be practically unflyable. As a short aside it may be possible to fly using the autonomous flight controller and limiting inputs to pitch and yaw but by human control it's too difficult not to use roll which is muscle memory by now.
What's next? By using a dampener on the rod and allowing pivoting in two axes we believe that this would allow freer flight. Watch this space.
UPDATE: at the present moment (October 2015) we've moved onto working with a plane and have achieved mild success using this vehicle. It's worth adding that the work performed here on the quadcopter is no longer necessary as our detector is now much less that 300g. I do believe that a quadcopter would be a very good vehicle to use for conducting these surveys though the cost is prohibitive to us as to achieve a flight time of even 30 minutes is beyond our budget.
We also worked on the dampener in the form of a rubber golf tee (the sort you find at driving ranges). This proved to be very effective. If we hadn't investigated the plane, we may well be using this method now.