[Jnadke]

Nobody has ever created a vacuum in FIRST robotics...

People have created partial vacuums, if that's what you mean.

There's a huge difference, a vacuum infers that there is no matter whatsoever inside the containment apparatus. With a partial vacuum there is air....
The difference is that with a vacuum the downward force exerted is 16PSI times the area of the suction cup.
With a partial vacuums, you have to use (16PSI - pressure inside) * area...
16PSI is standard atmospheric pressure.

There have been various attempts at partial vacuums... all methods employed suction-cup technology (as the rules state). Some just use regular suction cups, and press them to the surface, using force to remove the air and decrease the volume underneith the suction cup. Attempts to lift the suction cup then create an effective partial vacuum. At most, this system can only create equilibrium with the outside pressure. The partial vacuum is only created when you attempt to lift the suction cup.

Other attmpts include hooking the suction cup up to a cylinder, and then using another cylinder to increase the the total volume of the system, lowering the pressure. This, in effect, creates low pressure, and an overall downward force on the suction cup. This is much more effective than the first, because when you draw the cylinder, you create the partial vacuum. Any coefficient of friction between the surface and suction cup will be enhanced due to the downward pressure of the atmosphere.

My favorite, and probabaly the most effective, would be to use a one-way valve system and hook the suction cup to a cylinder. The air would be extracted from the suction cup (via equilibrium when you pull the piston), and then expelled out of another one-way valve. This would probabaly create the closest to a vacuum out of all three methods. I think I saw one team employing this method last year. I saw a motor driving a cylinder but I'm not sure if they were using a valve system (that would be pretty dumb if they weren't). As above, any COF would be enhanced.