We built something similar once before. It has an axle that runs the length of the front of the robot. Several wheels (or rollers) are on said axle. The whole contraption is lowered in front of the robot by means of a hinge actuated by a window motor or pneumatic piston.
The thought behind this is to put wheels or a skid plate in front of the bumper to push the ramp down.
As far as the ease of tipping the ramps, the ones at kickoff (which I assume are stiffer) can be pushed down very easily if you attack it at the right angle. If you have the resources, build a bridge and then try a few different ideas by building them and driving/ pushing the kitbot around on it.
Good Luck
