The View Up Here

Random scribblings about kites, photography, machining, and anything else

First RCAP Video

Posted by Tom Benedict on 17/03/2013

I know I said I had no real plans to stick a camera on my RC airplane. But I went and did it anyway!

I actually had a legitimate reason to do this. I found, during testing, that my plane suffers from a good bit of adverse yaw. I won’t go into a real discussion of adverse yaw and the reasons for it, except to say when you do an aileron roll, your tail wags out to one side. (The other side is “proverse yaw”.) This can be corrected by mixing in some rudder with your ailerons, but a better fix is to dial in differential aileron throw. This means that you set up your ailerons to move up more than they move down (or vice-versa). This can be done mechanically if you’re good with tuning linkages. OR you can do this using a computerized radio that lets you change the throw for each servo, in each direction. I chose the latter.

But the question comes up: how do you measure adverse yaw? The classical experiment is to fly the plane directly away from you, throw the ailerons hard over one way, then the other, and watch which way the tail wags. If there’s no adverse or proverse yaw, it shouldn’t wag at all. Mine wagged. So I dialed in some differential.

That’s when the wind picked up. It got harder and harder to see what the tail was doing. That’s when it hit me! Stick a camera on the plane!

In the kite aerial photography world, video mode on modern digital cameras has been a real life saver when trying to find out why your shots are blurry. Put the camera in video mode, put it up, and see what it’s doing! If it’s nodding up and down, the kite is pumping the line. If it’s swinging rotating back and forth, you might spread out your Picavet clips to help damp the motion. And if it’s just going all over the place, maybe it’s not such a good day to fly!

My hope was that I’d be able to do something similar with my plane: stick a camera on it, start video mode, and go through the motions. If I had any remaining adverse yaw, I should see the nose swing out as I entered a turn.

My camera “mount” was a copious application of blue painter’s tape to hold the camera in place. Sorry, no pan/tilt or head tracking. I’m too low tech for that. The camera was aimed up slightly because of the geometry of the plane. This kept most of the nose out of the shot, but it also meant that until I cut the motor, the ground wasn’t very visible. Still, I got the information I wanted. I still have some yaw to deal with, but not enough that I’m going to pursue it any more while I’m still using this radio. And I got a nice view of the town as well.

I’m also thoroughly convinced that KAP will still be my go-to technology of choice for doing aerial photography. Flight videos are fun, but nothing beats a tack-sharp high resolution KAP photo.

– Tom

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