I am Making a robot sandwiched between 2 of these guys(http://www.budgetrobotics.com/shop/index.php?shop=1&cat=28&itemid=143) and i would like to build a platform around the robot which "lifts up the robot" with some sort of leg(s) and holds the bot in the air so the platform can also rotate the bot to the desired heading(North, South, Whatever), and then have the legs come up so that the bot can once again travel with it's wheels on the ground and have the bot hold the platform up until it needs to turn again.
"boy if i only had an erector set" :'(
The first thing that comes to mind is some linear steppers. Or you could attach a couple of cams to some servos.
Why not simply use the wheels to turn the bot? Skid steering is as simple as separate motors for left and right wheels.
Or is your goal to have very accurate turning?
At any rate, how much will your bot weigh? You could use servos with arms--and the arms are the important part in determining how much weight you can lift how far with a given torque. Or if you need power over speed, you can create a lead screw mechanism with some threaded rod and a fixed nut.