I spent a few hours yesterday trying to perfect the gyro-stabilized camera (shown) in preparation for a test flight today. But even when I tweaked the settings it wouldn't take long before the gyro lost track of where "down" was and it ended up with the camera assembly at one side or another when it should have been level. It turns out that the drift cancellation wasn't perfect, which isn't too surprising. Unfortunately I really did need to it be perfect to avoid the little errors adding up over time and rendering the whole thing useless.
And then it struck me. I'm an idiot. The PLANE knows where down is! In many of our UAVs we're using IR stabilization to keep the wings level, and the way that works is that a FMA "Co-Pilot" sensor measures the infrared gradient between sky and earth on both sides and front and back, and uses that to establish a vertical axis. Then it just moves the ailerons and elevator to keep the plane flying perpendicular to that axis.
All I needed to do was to let that same FMA Co-Pilot drive the camera stabilization, too. Once I'd slapped my head and realized that the solution was right in front of me, it was a simple matter of removing the gyro, attaching the camera tilt servo to the aileron output of the Co-Pilot via a Y-harness (it's still driving the ailerons with same channel) and putting on a longer arm on the tilt servo to compensate for the lower throw distance of the Co-Pilot's signals. (All the other components and build instructions are as described here)
Today we tested it, and it work brilliantly. It's SO much better than the gyro-driven model. Here's a video of it in action:
The advantages include:
Doesn't need special calibration and doesn't drift. "Down" is alway down.
Much cheaper. Without the gyro, the cost drops from $100 to $25 (two servos and some aluminum)
Doesn't take up a separate channel. The camera stabilization automatically comes on when I turn on the plane stabilization.
Saves power because the tilt servo isn't always jittering with every gyro twitch.
But what about our UAVs that use gyro-based autopilots, rather than IR, for stabilization? There's no good way to have those autopilots drive the camera assembly, too. The answer is to bolt on a cheap ($49) and simple Futaba "pilot assist" sensor and controller, which uses visible light to do what our FMA units do with IR. You can just put it on the camera mount where the gyro was and it will keep the camera pointed down. It's not quite as neat as the ones that use the same stabilization system as the entire plane, but it's equally effective.