How To Set Up and Meter A Variable Low Speed Blower

[brockm87]

Hello,

I'm working on a project that has to do with using the Coanda effect to make a small hollow plastic ball about a quarter to half the size of a ping pong ball float on a vertical stream of air.

However, I'm not sure what size or weight of ball I will want to use, how high I want the ball to float, or how large the air flow orifice will need to be. The way I see it, I first need to have some type of variable speed air blower that will let me test different air flow rates. I plan on testing up to probably 3 cubic feet of air per minute, but might end up needing much less. I'm not worried about the ball or air ducting part of the problem, as I plan on using 3D printing.

Any ideas for how to achieve this cheaply?

Thanks in advance!
-Brock

 

[KrisBlueNZ]

Um... a motor with a fan attached to it?

I guess you would put it in a tube and force the air through a thinner tube with a constant diameter, in which you would place an air velocity sensor (Google it). Then you would implement a feedback loop to control the speed of the motor according to the desired air speed and the measured air speed.

You could start with an open-loop design where you just vary the motor speed by varying the voltage you supply to it, or use a constant motor speed and vary the diameter of the surrounding tube. This isn't my subject and those are just guesses.

You could also just borrow your sister's hair dryer and put a cutout on the tube, with a sliding plug piece, so you can let an adjustable amount of air out the side of it. Some vacuum cleaner handles have a sliding piece like that to reduce the suction when you're vacuuming delicate surfaces. Again just a guess.