Motor for lowering the bridge/ramp?

[pfreivald]

The correct way to answer this question is by doing the math. Figure out how much torque you need to lower the bridge, and then plan accordingly.

If this confuses you, talk to your physics teacher or an engineering mentor on your team. The problem is high-school level physics to determine the torque to lower the bridge, the force necessary to create that torque with different lever arms from your robot, and also to determine the various times that (ideal) motors would take to perform the task while creating that force.