Rotation coordinates help

Question

I have no idea how to explain this. I am trying to create a
movie that explains a bit about magnetism. I have 3 mc-s.
The first, MC1 is static. I want to use the dimensions of
this movie as constraints to the movement of a second movie.
the second movie MC2 should go no higher than the top of the
first mc or lower than the bottom of the same mc.
The third MC3 rotates, the speed of this rotation should
constrain how quickly/slowly MC2 moves.
it is set up this way.
MC1 does nothing.
MC2 starts in the middle of MC1 and moves to the topmost
limit
MC3 starts to rotate
by the time MC3 has rotated 90 deg, MC2 should be at the
topmost limit of the boundaries of MC1
MC 2 should then start to descend.
By the time MC3 is at 180 deg, MC2 should be back at the
centre
By the time MC3 is at 270 deg MC2 should be at the bottom
most limit of MC1
by the time MC3 is back to 0 MC2 should be at the centre of
MC1.
How can I programmtically constrain these things. I can do it
by tweening, but that's a pain in the backside and it isn't
scalable?
I hope this is clear.
Thanks
one mc that rotates around it's central axis. I have another
mc which should go up and down

Answer 1

Ok, I tried your "empty MovieClip" method, and it seems to work well. Please look at my code and see if I am doing it the most efficient way.
These are symbols in my library:
Clean (MovieClip) - Black stage sized rectangle to clear the buffer.
Square (MovieClip) - Blue (100x100) Square centered on the crosshairs (so it can rotate on its center)
// BEGIN CODE //
var bitmap:BitmapData = new BitmapData(stage.stageWidth,stage.stageHeight,true,0xff000000);                    
var buffer:BitmapData = new BitmapData(stage.stageWidth,stage.stageHeight,true,0xff000000);
var image:Bitmap = new Bitmap(bitmap);
addChild(image);
var clean:MovieClip = new Clean();
var container:MovieClip = new MovieClip();
var square:MovieClip = new Square();
container.x = stage.width/2-square.width/2;
container.y = stage.height/2-square.width/2;
container.addChild(square);
square.x = container.width/2;
square.y = container.height/2;
addEventListener(Event.ENTER_FRAME,onEnterFrame);
function onEnterFrame(event:Event):void {
    square.rotation+=5;
    buffer.draw(clean);
    buffer.draw(container, container.transform.matrix);
    bitmap.draw(buffer);
// END CODE //
A few questions I had about the code:
1. On "var square:MovieClip = new Square();" should I keep MovieClip like I have, or use Square?
2. If I make a Square.as file later, and have to use Square, do I retain MovieClip properties from my library symbol?
3. For memory management, do I need to set my MovieClips to null, or anything else like that in some finishing function?
Sorry about all the questions, I just want to get it right the first time. Thanks.