Move assembly parts in specific points

Hy everyone! First post, I really need your help. I'm new to Inventor, and to understand how it works I watched tutorials and used the built in guide, very usefull.

But still, I have a problem. I'm trying to assemblate trusses with spherical joints, and it seems to be working, but I can't control the position of the elements, and this brings to problems when the assembly gets bigger.

I try to be more specific. I'm trying to rebuild the Ron Resch Origami pattern, (http://www.ics.uci.edu/~eppstein/junkyard/resch.pdf), and I did one of the inner big triangles. If I try to go on and assemble more parts, I get a lot of errors (or, the programm turns some spherical joints of. So, I want to fix the position of the spheres, that represent the points of intersection of the lines, so to build the structure in his flat condition. Later, I'll try to move it and to make it close.

I tried with the first central sphere, created a Work point using the axis of the sphere, and that worked (it even locked the sphere in that position, but letting me to rotate it: perfect!). I grounded the work point and I've seen that the sphere seems to follow his movements.

How to position the other spheres in a precise distance from the first one? I could create workpoints for all, but how to put it at, for example, 2 metres left and 3 metres up the first one?

This is the file I'm working on (the triangle in the sketch is how it should be, I was thinking of using it to get the coordinates for the work points): http://www.megaportal.it/ld3/assembly.rar

I'm really sorry to bother you with this. I used a lot of words to explain it, hope it's not a problem.

Thank you a lot for any help! Really appreciate.

p.s.: and sorry for the bad english :wink: