RE: How do i setup a mix for knife edge?
As Stek says, these two mixes, rudder-elevator and rudder-ailerons, once settled, should remain on all the time. The way to do that is assign them to any switch, and select the NULL position for activating the mix. Null means no matter what position the switch is in, the mix is on.
Normally, with almost any aerobatic model, flying along at straight & level, if you give rudder in one direction or the other, you will get nose pitching down to some degree, and some degree of roll, which can be proverse (roll in the direction of the rudder turn) or adverse (roll opposite direction of rudder turn).
Ideally, you would like to be able to apply rudder in any attitude at any speed, and the plane would respond with yaw only--no pitch, no roll. There are models that come close to this behavior, but they are not easy to find. Knife edge mix will get you closer to this behavior, which is why it's normally on all the time. I repeat, the model's reaction will be different (usually) for left vs right rudder, and vary with airspeed (and perhaps also with attitude). So mix carefully with trial runs using both left & right rudder, and do it all at normal cruising speed--somewhere between half & 2/3 throttle, depending on how 'overpowered' your model is.
I usually see recommendations to start off with mixes of 2-3% for first run, and adjust from there. But you need to know whether it's + or - some percentage. And the conventions are different from one brand of TX to another. What I normally do for setting up my first approximations is set the mix at 5%, then work the controls on the bench. What I want to see is--with left rudder, the elevators come up a small but visible amount, and the ailerons move a small but visible amount for left roll--left aileron slightly up, right aileron slightly down. Then with right rudder, I want the elevators to do exactly what they did for left--both come up slightly; and ailerons deflect for right roll--right aileron up, left aileron down. Whatever you get for + or - mix indications, don't worry about the signs, just get the right control surface response.
You can do all this with the RX turned on, TX turned on, go to the mixing programs, twirl the knob and see the immediate reaction on the model.
I must repeat emphatically my earlier comment, that there's no point in addressing knife-edge mixes until you've got your CG just where you want it, control surfaces trimmed for neutral behavior in straight & level flight, thrust offsets vertical & horizontal for straight up at WOT, straight down at idle, and no change in pitch with change in throttle. Almost forgot aileron differential, which should also be settled before coupling mixes.
As to trimming procedures, there are pages on the NSRCA website, the mini-IAC website, and a few others. Take your pick. I'm sorry to say there are inaccuracies (most fairly obvious) in just about every one of these I've looked at, but on the whole they are useful, especially to someone who is not an expert (as I'm not). The most important consideration is to do the trims in the proper order; otherwise you'll be making trim changes at step 7 that will throw off your adjustments in step 2, meaning you have to go back and do 2 through 7 all over again. Thrashing around like that, you can spend a year and still not get your plane to fly straight.