I thought that rudder on right stick for a 3ch was right; because you are mostly using aileron for turning, and the right stick becomes the "turn" stick, whether it is using the rudder (3ch) or aileron (4ch).
However, "thatplaneguy" (TPG) makes a good point. How will you learn rudder if you keep moving it around?

Also: during takeoff whilst still on ground, I want to control heading with the rudder. Right now I have both 4 and 3 ch airplanes; and on my 3ch, "heading" is on the right, and on my 4ch, it's on the left!!! Wouldn't it be better in the long run FOR BEGINNERS to just keep the rudder on the left? The worst thing they would to then would be to try to turn with the rudder rather than the aileron. That's not always a fatal error; not like using down elevator to make a turn!!

I'll admit to knowing very little about how an airplane REALLY works, but I was going to weigh in on the holding rudder, on the basis of the resultant forces. Rob2160 found the perfect link to explain this. But here it is in my words

When you have cross wind, some of the wind is trying to push you to one side, some of it is along the path of the craft (this is breaking the wind into its vectors). In the absence of this force, the aircraft would have a vector parallel to the strip. However, the sum of these forces results in the airplane moving in the direction of the strip, plus a little bit to the side. The nature of this can be deceptive, as the aircraft HEADING is straight down the strip; but it's moving sideways!!

Now if you want the aircraft to follow a vector parallel to the strip, you need to introduce a force offsetting the sideways force. Some people think this is caused by the shape of the craft, some by the engine thrust vector. I think it's the thrust vector. You use the rudder to change the heading of the plane. It is just enough so that the thrust vector in the direction opposite of the wind is equalized. The aircraft will have a slight heading into the wind; but it's vector is parallel to the ground. This looks like all the crabbing videos although maybe crabbing is not the correct term.

Now if that is correct (I'm no expert right so maybe this is wrong. But the dynamics and vectors sound right, and agrees with NASA and they put people on the moon....) then if you release rudder; you take away the small component of force maintaining your heading and vector.

Did I miss something?

Regards