Note: I added those 2 vertical beams to delay the carts until both cubes slide on the buttons. Also the last bridge is not so stable, i guess you can make it better if you have the patience.
Bridge Constructor Portal Level 42 (Cubachinko) Convoy Walkthrough, Cheats, Solution for Android, iPhone, iPad, iPod and PC (Steam).
Note: This is "Bridge Constructor Portal" by "Headup Games"