this looks like a job for vectors!!!!!!!!! (math vectors)

they allow you to get angles for stuff like this, and weight each angles influence on the overall outcome.

<img src="http://upload.wikimedia.org/wikipedia/commons/thumb/8/88/Vector_by_Zureks.svg/300px-Vector_by_Zureks.svg.png">

youll have to set the middle parts angle to the angle from the initial point to the sense of a vector which is the average of the vectors of your top part and bottom part.

so first youd get the sense of your top and bottom like this (handle the vectors x and y seperately)

for the top vectors x youd make it:

cos(top.angle)*10 (this is the sense for x)

sin(top.angle)*10 (this is the sense for y)

and youd get the sense of the bottom in the same way

then to get the x and y of you middle sense youd do this

(((cos(top.angle)*10 )+(cos(bottom.angle)*10 ))/2)

(((sin(top.angle)*10 )+(sin(bottom.angle)*10 ))/2)

to find the middles angle youd do this

angle(0,0,(((cos(top.angle)*10 )+(cos(bottom.angle)*10 ))/2),(((sin(top.angle)*10 )+(sin(bottom.angle)*10 ))/2)) and that should give you the proper angle.

you can just paste this in and it should work

angle(0,0,(((cos(top.angle)*10 )+(cos(bottom.angle)*10 ))/2),(((sin(top.angle)*10 )+(sin(bottom.angle)*10 ))/2))

when the angle difference between your top and bottom is greater than 180, the middle will seem to flip, like it already did in the original i have no idea how to stop this atm.

but the crossover problem is now fixed