After much testing it turns out that long arms and 9" props in a Y4 configuration has almost no yaw authority at all!!

It made the copter practically useless for AP as you couldn't keep it straight let alone pan a shot.

So I decided to go with a standard tricopter and got myself one of these:

It's a ToughTilt mechanism from flitetest.com and it's rock solid. It has an almost hydraulic feel to the movement.

After a test with the 9" props it was obvious I needed something bigger.

So I went with 850kv motors and 11x5" props. This gives me a nice 50% hover: