# Can anyone help us in the design of the articulation of a symmetrical structure?

Hello: We are designing a structure whose opening and closing must be symmetrical (see attached images).

The angles "beta ß" in the middle bars of the two arms on each side must always be equals. Same with the angles "gamma" between second arms (in green) and the stringer (in blue).

The angles "alfa" between the underrun and the first arms (in red) are always the same due to a mechanism which obliges the symmetry.

Right now the unions between the arms (angle beta) and second arm and the stringer are simple joints (see picture) without limitation in the rotation and as a result or this, the structure rotates and the angles beta and gamma becomes unequal (pictures 3 & 4).

We can only use the arms, the joints, the stringer and maybe the underrun, to Insert the mechanism that creates the limitation of rotation forcing the opining and closing to always describe equal angles.

The mechanisms can use sprockets, zippers, cables, chains, ...

Can somebody of the community help us in this design?

Best regards.