I'm not positive, but your trackball looks a little deflated to me.

Kidding... Normally I am opposed to scissor jacks, but I like the idea in this particular situation because it should make you much less likely to tip, since the weight of the trackball is focused directly over the robot.

Is the ball guided over the overpass by your manipulator after it is jacked up above the 6' 6" level? It appears that way...

EDIT: Yepp, you explained it while I was posting haha