[Bruceb]

My opinion. Don't even think of trying to drive up to the bridge and then use an arm of some kind to tip it down. You have to have extremely good depth perception to make that work unless you have some way of letting the robot do it by itself. Remember, most cases you are on the other side if the bridge at some distance and partially concealed by the bridge.
Better, lower a ramping device with an over center latch and just drive up to the bridge. Let the weight of your bot push the bridge down.
see here
http://s1121.photobucket.com/albums/...t=100_0013.mp4

Hope that helps