Re: Suction as a method for possessing balls
 

Maybe they should attach just a few Ball Magnets :)

Re: Suction as a method for possessing balls
 

So we could use FP motors, maybe attached to the 3 inch computer fan to speed it up?

Re: Suction as a method for possessing balls
 

I doubt the computer fan blades are what you want...they are designed to move air gently out of a computer case. The suction fan in a shop vac is quite different, you might see about getting some type of inexpensive vacuum cleaner and taking it apart and seeing if you can adapt the FP motor to it. Consider the RPM that the original motor runs at, though, and see if it's a good match for the FP motor.

Re: Suction as a method for possessing balls
 

No, an axial flow fan is not designed to create much delta P, only flow. You need an radial flow device, like a vacuum impeller. As a rule of thumb when looking at impellers, flow is proportional to the impellers' width, while pressure is proportional to its diameter. So, for max holding power, use a large diameter, narrow impeller, or better yet, a 2-stage impeller system.

Re: Suction as a method for possessing balls
 

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

Re: Suction as a method for possessing balls
 

I hadn't thought of hooking two shop vacs in series, but I guess that could work. I was talking about two stage impeller designs. The vac unit we used in 2008 was a two stage impeller, it had two impellers on one shaft, separated by a flow straightener. Some vacs have wide single impellers for max flow, some have two narrow impellers for max delta P.


Choose wisely grasshopper.

(my cultural references are way out of date:D )

Re: Suction as a method for possessing balls
 

how would you suggest hooking the fisher price motor to the shop vac impeller?

Re: Suction as a method for possessing balls
 

We are currently in the process of replacing the AC motor from a Husky shop vac. with either an RS-555SH Mabuchi motor or an FP. The results of testing with the Mabuchi will tell us if we need to go to the FP.

By the way, we will most likely be gearing up which ever motor we decide to use. We currently are estimating we need something in the neighborhood of 18K RPM.

We had to custom build a shaft to replace the one that is part of the AC motor. If direct driving with either motor works, we will post up pics later tonight or tomorrow. If we need to gear up, that will take another day or so to complete.

Re: Suction as a method for possessing balls
 

Has anyone considered drawing a vacuum using a pneumatic piston? I would think the suction force from the piston would be much greater than from a shop vac. Down side is that if you have a small leak, once the piston reaches the end of it's stroke, you've lost your suction.

Just a thought that I want to tryout myself.

-Chip Tucker

Re: Suction as a method for possessing balls
 

Is anyone actually putting a suction mechanism on their robot? The gray area in the rules makes it seem like a judge could possibly rule it illegal and DQ the robot. And, if the mechanism is too strong and the robot accidentally goes over a bump with the ball, it would be a penalty.

Re: Suction as a method for possessing balls
 

On a suggestion from another teams mentor, I just cannibalized my 18v dewalt vaccum. It took me about 10 minutes to swap the motor in it for a fp. I think we will be using it on the robot.

Re: Suction as a method for possessing balls
 

Phenomenal idea. Too bad we didn't have one of those to use, it would have made this process a little easier.

So far we have determined that using a 1:2 gearing increase and a FP motor on a 6 in diameter impeller from a $20.00 Husky shop vac. will do the trick. We just need to make an adapter plate and assemble the whole thing tomorrow. Heck, we might even put the vac back together when we are finished. That way we will protect the impeller from damage due to field debris and might pick up a coin or two to boot.:yikes:

Re: Suction as a method for possessing balls
 

Which dewalt vac did you use, the DC500 or the DC515?

Re: Suction as a method for possessing balls
 

the dc 515
I just looked at a parts diagram for the 500 and it looks like pretty much the same motor & impeller.

Re: Suction as a method for possessing balls
 

What gray area? What part of the rules would indicate it is disallowed?