the KK board will counter external factors such as wind pushing the tri around to a certain extent, but it will not actually try to maintain level flight. You can test that by holding the tri in your hand with the props spinning, then slowly tilting it. There will be no reaction from the KK. If you are a bit more abrupt it will indeed spin up the sinking prop, but that is not really enough. You can set the pots to be more sensitive but then the system will soon overreact and start to wobble.
Basically the gyros in the KK will only react to acceleration. Systems like the FY-20A do more, they actively try to assume a flight attitude which they see as level. This was a bit of surprise to me as well, I also assumed the KK would do that.
Regarding your problems I suggest you try the following:
0 - check CG. The tri needs to very nearly balance on a finger placed at the intersection of all three arms. Adjust battery position as required to achieve that. Also, make sure the direction indicator of the KK board is pointing towards the front.
1 - set the Tx to plane mode (not heli) to take the swash plate mixing out
2 - put the tri on a hard surface, at least 5x5 meters, tail towards you, and adjust all three pots on the KK to mid position
3 - spool up to a point without taking off, then apply rudder. If it doesn't turn the right way, reverse the channel in the Tx
4 - likewise, try aileron and reverse if the wrong prop rises (one of them should spin up)
5 - same for elevator, try and reverse if required
6 - spool up a bit more until the tri wants to lift off and starts sliding around on the floor. See if you can control it with elevator/aileron/rudder. Note which way it wants to slide (e.g. front and left). If it wants to yaw, apply trim on the rudder stick to counter that.
7 - now, throttle up to bring it off the deck quickly by 2 feet or so, applying stick as required to counter the movement from #6 (in this case, back and right).
8 - adjust trims on the Tx as required (in this case, trim down and right a couple clicks)
That should get you airborne. After that, land it and adjust the pots on the KK. Basically, turn them up (clockwise) a bit at a time and test fly until you notice the whole thing become skittish. Then back them off a bit again. That would be the maximum setting you can have.
Note though that the whole thing flies pretty much like a heli at this point. Letting go of the sticks means it will start to drift and sink randomly.
I already have the FY-21 AP with return home function, are you saying if I connect this between the Rx and KK controller, this will stabilise the tricopter platform?
As far as I understand their manual, the FY-21AP only works with fixed-wing aircraft. Though there's nothing in the FY-20A manual about copters either. Fyetech say the 21 is an enhanced 20 with additional functionality (which may or may not be true) so it might work as well, I just have not been able to find a single post anywhere saying something about the combo FY-21AP + tricopter. Or any copter for that matter. What I did find was this: http://www.helifreak.com/showthread.php?t=250810
Maybe drop Fyetech an email and see what they say?
So what's the purpose of the KK board?
Basically, do the mixing of the motors as required and provide some limited stabilization functionality, but no self-leveling.
Have you got a phone number?
Yes but I'm not at home right now. I'll PM you my office number, you can call me on Monday if you want.
As far as I'm aware, the FY-20 and FY-21 are not designed to stabilise anything but a fix wing aircraft, i.e., there is no throttle input yet strangely enough there is a throttle out.
Yes, they do not control the throttle. The FY-20A only has aile/elev/rudd channels, plus the mode selector. The manual clearly says it will take care of attitude control but the pilot has to take care of airspeed. In the case of the KK board that's ok because throttle is mixed onto all three throttle channels.
Edit: on a technical note, it seems the FY-20A actually uses accelerometers, while the KK boards have gyros. That would explain the difference I guess.