I have put together this discussion thread to aid in planning Ecosynth work in Panama. Some of our discussions have happened on email, but I am going to try to start answering and posing all questions on this forum.
Helene had a few specific questions recently that I want to try to address:
1. Platforms: We think an octocopter (8 propeller) multirotor copter is best suited for the size of area you are interested in flying (50 ha over one mission). We are preparing a common parts-list / budget for such a device now. We have a setup using the Arducopter system and several batteries that can fly for about 30 minutes.
2. Launch: It is best to launch from as close to the mission area as possible and ideally less than 100 m away from the area of interest (AOI). One thing we have done in the past in closed-canopy forests, is to launch from inside the forest near a gap, fly horizontally into the gap, then vertically up and out for the mission: see a video of yours truly doing that here.
3. Climate: The climate in Panama can be especially hard on electronics, including batteries. This is really new territory for us. Some of the most moisture sensitive components are on the electronic speed controllers, ESCs, and failures there can quickly lead to crashes. It will be worth testing the use of 'conformal sprays' for water-proofing these sensitive electronics. Links to some examples: PDF guide for protecting Mikrokopter style ESCs, forum chats about conformal spray, and a product link to All-Spec TechSpray.
As for the lipo batteries, my biggest concern would be corrosion of the 'Deans Plugs' terminals. The lipos themselves are tightly sealed, but the terminals are exposed. A salty, humid climate protocol might need to be developed to weather proof the gear and prevent corrosion.
You reported the winds at around 15 kph (~9mph), which should be OK for most normal flying, but is right on the edge of what we consider our normal operating margin. We have been able to complete our 15 minute 250 m x 250 m mission in winds up to 24 kph (15 mph), but in general such conditions should be avoided.
Now, I have some questions!
What is the terrain like in the AOI?
Do you have existing understory digital terrain models for this location? For example, as would be obtained from LIDAR or a ground survey?
Can you venture a guess at what the wind speed is like above the canopy, say 100 - 200m up? It will be necessary to fly higher over the forest to capture the entire AOI in one flight, compared to the 40m above the canopy when we fly in Maryland.
I've been looking over the BCI LIDAR Canopy Height Map (CHM) to try to identify a potential launch spot for our mission. Because we are working at much longer distances than normal (1000 m x 500 m or approximately 7000 m flying distance for a mission with 50% overlap at 150 m above canopy top) I am really interested in maximizing the efficiency of our flights, in other words, minimizing distance traveled.
The use of Arducopters means we could technically launch from anywhere within a reasonably close proximity to the area of interest. There are no 'convenient' open grassy fields or parking lots at BCI, the island is covered in a dense closed canopy tropical forest reaching heights of 50 m tall! This will most likely require us to fly up out of a canopy gap. When gaps are formed from fallen trees, they will quickly be filled by new growth competing for the new supply of sunlight, so it is rare to find a gap with little vegetative cover for an easy launch.
At our Maryland Knoll and SERC sites we would fly out from gaps in the canopy of about 20 m x 20m (Knoll) or about 20 m x 30 m SERC. This requires identifying a gap, identifying a relatively more clear area under the canopy and adjacent to the gap, then piloting the craft first up a few meters, then out over the gap, then up out of the gap, as in my crude drawing below. You can also see a video of me doing this here:http://ecosynth.org/video/flying-hexakopter-up-through-canopy-gap
Gaps on BCI close very quickly not only from the bottom, but also on the sides. Lianas (woody vines), plus extra leafing up of vegetation on the sides of the gaps, mean that the sort of sideways move depicted in this image probably won't be an option on most gaps more than a year or so old. It seems to me more likely that we'll be able to find one or more really recent gaps where one could stand in the gap to launch.
Can the copter launch from being held by hand in the air? I suppose it could takeoff, but landing would be a problem? How large a flat, uniform area would be needed for landing? I'm wondering if we could carry a piece of plywood into the forest and temporarily set it down in a young gap for the launch and landing?
We took stereophotos from helicopters in 2000 and 2008, and set up 5-8 targets in and around the 50-ha plot to use as ground control points. The targets were sheets of cloths (about the size of a twin bed sheet) with a bull's eye painted on it, suspended from rope on four corners to get it above any ground vegetation. These targets were easily visible from the helicopter. So I have no doubt you can find large recent gaps in which to launch the UAV (much larger than the one depicted in the video where you are launching the UAV in Maryland). We found these by asking people who were in the plot to identify the approximate coordinates of recent gaps, and also just walking around for a half of a day to assess which gaps would work.
The issue of taking off and landing is more difficult. If you are lucky, there will be a really recent gap that is pretty easy to work in, but I wouldn't count on it. One idea is to do what we did - suspend a cloth above the vegetation and land the UAV on that, especially if the UAV can be hand-launched.
Perhaps take-off from a portable folding table, like a card table, and 'landing' in the catch sheet. As was mentioned earlier in the thread (I think Helene brought it up?) some plane systems are designed for soft landings in nets. The issue would be to try to avoid things that could tangle the props which could lead to motor burn out.
We could definitely find gaps suitable for launching from a card table and landing on a sheet. Would just a regular bedsheet do?
The material has to be lightweight and strong. We have used both actual bed sheets, and also white cloth (widest cloth that they sell) we bought in a fabric store in Panama.
It is also good to get a lot of rope to hang the sheet. sometimes the nearest tree to hang a corner is a long way away in a big gap.
Perhaps we could use a tarp? I am concerned a sheet might be able to catch in the props. Stephen thinks that a tarp / sheet catch landing is probably doable - but we should anticipate breaking props and landing gear and will probably want to consider armoring the camera.
So it sounds like this is our take-off and landing plan:
Launch from a gap off of a card table
Land in the same gap into a tarp / tough sheet suspended from the trees.
yes, a tarp would work. We didn't use a tarp because it is not very visible from above and degrade quickly in the tropical sun.
We were able to pull the sheet taut, which should help not damage parts. But if the tarp/sheet is up for a while it will start to sag because it collects rainwater.
Yes, being taught could help. I don't have a good sense of how long it would need to be left out. I expect if it were out for too long it would effect growth of plants underneath. But on the other hand it might be a pain to set up every week.