Ok some careful math analysis showed that I should keep the other generalized coordinates absolutely stiff and solve the whole system by varying one generalized coordinate at a time.
I'm very happy that I found this forum, hello everyone.
I'm studying Lagrangian Dynamics and I can't figure out how to find the generalized forces in a setup like this:
____ ____
| | ___ | |
| b1 |===|___|===| b2 |
|____| |____|
--->x...