Thank you for the posts!
I am sorry that i didnt wrote earlier, had much to do. But i found in a book some possible calculations for the forces of the system (do not know if they are rigth.
I wrote a little matlab script to calculate the forces at every possible angle of the crank system. The results show me very high forces at pi and 2*pi of the system. (I think thats because of the singularities.
My question is how to solve this problem. The system should not have fast motions, in the contrary it should move slow and transfer forces! Or is it better to avoid this positions and rotate only between 0 and pi? (I would like to use the whole rotation, if it is possible)