Suction as a method for possessing balls

[Culvan Van Li]

Originally Posted by martin417

for max holding power, use a large diameter, narrow impeller, or better yet, a 2-stage impeller system.

I've seen discussions of Shop Vacs on Vacuum forming boards. According to them a decent shop vac will pull 3 inches of mercury or about 1.47psi. They didn't seem to think that a second shop vac in line with it provided a significant improvement, but they're looking for significantly lower pressure than a shop vac can provide. They might have discounted double the "delta P" as not significant.

I've seen a lot of people say fan for this idea, but an impeller is the fan-like device inside a shop vac. It is designed to work better for this type of application. I'm amazed with the performance people are saying they are getting with a 1" hose. That's only 0.785 square inches. Assuming 1.47 psi, then the holding force is 1.15 pounds. The ball weighs about 1 pound so I'd expect it to barely be able to pick up the ball. A 2" hose would bring the force up to 4.62 pounds and should provide a pretty good grip. Of course a larger grip surface will make that much stronger. In fact is seems very plausable that a suction cup mounted inside the frame could get a good grip.

I'd recommend that you don't plan to go over the bump while possessing a ball. I cannot think of a configuration that will work where the ball does not get wedged under the bumpers. Teams always seem to find a way to do what I think is impossible so I'll be watching for it at the regionals. I guess a 6 wheeled robot with an actuated center wheel could do it. Still, I think it's unlikely.

Andy