Creating a Coandă Effect Staircase

The Coandă effect, as James Bruton explains in the build video below, has to do with the tenancy of flowing air to stick to a convex surface. It’s the reason you can suspend a ping pong ball with a jet of air. It's an interesting engineering concept, which he set out to demonstrate with a sort of curving air staircase.

His rig uses three curved surfaces to guide the air flowfrom DC electric ducted fans (EDFs) that sit on each one’s base. When a ball is tossed into the first (and lowest) fan/duct it shoots up, but instead of continuing in a vertical direction, it follows the curve, outputting to the second duct assembly. This in turn shoots the ball to the third duct, which pushes it up and in the direction of the duct.

Or that’s how it’s supposed to work. In reality, this sequence only happens some of the time, but is nonetheless a neat demonstration of what may be an otherwise unfamiliar concept. As Bruton puts it, he’s “not too unhappy with how this works,” and outlines a few ideas for how it could be improved.

Electronics include an Arduino Uno with a potentiometer for user interface, and a DC motor driver that controls the speed of the fans. He also implemented a feeder mechanism to place the balls without tossing them, with speed control via another driver, and a set analog output from the controlling the Uno.