After our success with the Peersonic detector working in-flight (see our blog post here) we decided to push on and get some actual field testing done! This will be the first time we've attempted to use the UAV to record actual BATS!
The first thing to do was identify an area in which is likely to have some bats flying around and that we can fly the UAV at. Fortunately, our flying site in Oxfordshire has a lovely line of trees with woods and hedges at both ends which look quite promising.
During the day we set up a flight path which took us down the tree line, over a hedge at the end, looped round the wood then cut in towards the tree line again heading back towards us and past the wood at the end with a final turn taking us over a hedge and back to the starting point. The whole route took about 6 minutes 30 seconds to fly.
Although the description is all very well and good a picture of the route might be more useful:
We flew this a number of times to ensure we weren't too close to the trees or in danger at any point. To do this we used a FPV (first person view) set up on the plane in order to assist in distance perception to trees. It turned out that this was fairly crucial as during the first run we were a little close to the trees. After some minor changes to the flight path we repeated the route and were happy with it. We decided on an altitude of 15 m to make sure we'd have more than enough clearance for any objects. Here's the plane's view of the flight path:
On to the night flying!
With the route set, we were ready for the night flying with the detector. A bit of fiddling later and we'd set off on our first pass of the route. It's a strange feeling watching the lights of the plane sail off into the distance. It's great to see how stable the plane flies at night as well when the wind was a little lower.
After two passes we decided to take a walk up to the woods at the start of the tree line to see if we could find any bats using our other detector. Happily we noticed one or two commuting down a hedge line that connected to the woods.
A short re-route of the flight plan later and we had a flight running down the hedge line at an altitude of 8 m and 15 m horizontally from the hedge.
Have we recorded a bat?!
When looking through the sonogram, we noticed this:
Between 204300 and 204400 ms there's what looks like a 45 kHz bat call. The sound lasts for a duration of approx 7 ms and has a classic hockey stick appearance. It's also at bang on 45 kHz which ties in with a 45 pip.
There is however, a lot of ultrasonic interference from the motor/propeller and we want to be sure that this is a bat.
HERE'S THE LINK TO THE RECORDING:
If you have any experience we'd really appreciate your thoughts. The full .wav file is accessible via this link (right click - save as). Please feel free to download let us know what you think.
As always, we'd like to acknowledge Peter at Peersonic.co.uk for his constant support and providing the recording equipment that has been so useful in progressing this project.
Thanks, Tom & Tom
Following on from our post here about our new detector from PeerSonic we went ahead and did some testing with this on the plane.
We wanted to ascertain how the plane/detector performed for two criteria:
For a quick reminder, here's the set up we were using as modelled by Tom A:
The position of the detector on the wing tip is not ideal. It leaves the detector open to damage upon landings and adds additional weight at an extreme position relative to the centre of gravity which must be counterbalanced and gives rise to instability. For flight testing, we balanced the weight of the detector with a bag of sugar on the opposite wing.
We're currently working with Peter at PeerSonic for a solution to this where we'll hopefully have the microphone separate from the detector and be able to mount the detector more centrally (relative to the centre of gravity for the plane).
So, how did it fly? There was a noticeable instability in the roll element of the flight but nothing that the flight controller stabilisation and pilot input couldn't correct. This was more apparent when windy but the plane was definitely flyable in this configuration.
For the ultrasound detection testing we flew two passes at roughly 10 m from the detector horizontally and at altitudes of approx 10 m and 20 m. Here are the sonograms from these passes:
The ultrasound source is easily visible at 10 m, especially as it's a different frequency to the propeller interference. At 20 m we can see that the ultrasound source is hardly detectable.
Fortunately, we expect bats to be somewhat louder than our ultrasound source and hope to be able to detect at 20 m and perhaps even further.
So, great news! We now have a working prototype for the Bat UAV! In the next post, we'll be doing some actual field testing and see if we can record any bats!