are one of the most popular aerial photography aircraft for a good reason: they're cheap, stable, tough and easy to modify. In an earlier post
, I described how to upgrade one for better performance. In this post, I'll show you how to install a camera for great Google Earth mapping, producing high-resolution, stitch-ready imagery like this
[UPDATE: some of you have wondered why I'd want to use this foam glider when we have several other excellent UAVs and aerial photography aircraft, some of them including such niceties as stabilized camera mounts. The answer is that often there's no runway or clear landing area where we're working. The aircraft with fancy payload platforms hanging beneath them are designed to land on a smooth surface, and crunching into a hillside will damage the camera along with its mounting equipment and often the plane itself. The EasyStar, by contrast, is hand launched and can land anywhere, and the camera is protected inside its soft foam body. And if it hits anything or anybody, it won't do any damage.]
The secret to getting shots that you can mosaic into a large-area map is to take a lot of them, as quickly and at as high resolution as possible. That usually means a digital camera shooting straight down in continuous mode (which takes a picture every half-second or so as long as the shutter button is held down), with a high shutter speed to avoid motion blur. For various reasons, the usual ways to trigger a camera remotely--IR shutter triggers, USB connections, or stop-motion settings--don't work with continuous mode. So the only way to do it is to hack into the camera and find the circuitry that triggers the shutter (which is too scary for me) or to have a servo manually push down on the shutter button. Here's how to do the latter:
The first thing is to carve a bit of foam out of the sides of the EasyStar's instrument bay to fit a standard pocket digicam (I'm using a 10 megapixel Pentax Optio A30). A big kitchen knife will do it. Then carve a hole in the bottom where the lens will go when it's extended. Finally, because you've weakened the body by carving away that foam, you'll want to epoxy in two reinforcing strips (I used spruce spars I found at the hardware store), which will also serve as the mounting rails for the camera.
When you're done it will look like this, with a little extra carving at front and back so you can place the camera properly (I carved a bit too much foam from the left side of the plane, so I put in a thin plywood sheet to reinforce that area):
The next thing is to epoxy in the servo (the blue thing in the picture above) that's going to depress the shutter button. This is simply a matter of carving out a servo-sized hole in the side of body, after measuring carefully where the camera's shutter button falls when it's on those rails. Make sure you've cut off all non-essential servo arms and re-seated the arm so it it's fully pushing down the camera button when you turn on the channel 5 switch on your transmitter before gluing it in. From the side, that looks like this:
That's pretty much it. When the camera's in, it looks like this:
And from the bottom, it looks like this:
You're ready to go! Just remember to rubber-band everything in tightly so it doesn't shift in flight, turn off the auto power-off on the camera, set it to a relatively high ISO setting (800 works for me) to avoid motion blur and put in a high-capacity memory card (at least 2 gig). Once the plane's in the air and flying smoothly at around 200 feet you're ready to toggle the channel 5 switch and take strips of shots to later composite into a full-area map. Or just put in an autopilot and turn the EasyStar into a proper UAV and can follow those strip tracks itself.