A Ducted Fan is a little like an electric jet engine. They are often used in model aircraft to in place of jet engines, and hold a place of honor in every sci-fi and futuristic aircraft I've ever scene. Ducted fans offer the promises of high power densities in small protected packages without all those unshrouded propellers tips whipping about.
A Ducted Fan is made up of three primary parts: the impeller, the shroud, and the motor. The motor is of out little Pololu FA-130 Motors. The impeller blades are fixed a 45 degrees and the hub is large enough to cover the face of the motor. The shroud is a bit trickier. For the ducted fan to work properly it has to come as close to the spinning ends of the impeller as possible without touching. It also has to have enough strength to hold the motor in place as it spins. I designed the shroud to have a 0.5mm gap between its inner surface and the impeller blades.
I wasn't expecting much from this project, Ducted Fans are notoriously hard to design. So I was shocked when it shot across the table after I applied power. This little puppy produces some thrust!
We can quantify the thrust produced using a small digital scale and a test stand. The test stand holds the Ducted Fan above the surface of the scale, so it can pull in air. The fan is installed face down, with the exhaust pointing up. Any thrust produced will push down against the surface of the scale through the test stand. Thrust will be quantified as an increase in the weight registered by the scale.
To keep things simple, I set up the Ducted Fan, test stand and batteries on the scale and used the tare function to zero them out, so at the start of the test, the scale reads 0.000kg.
With the fan running the scale reads 0.012kg. This little Ducted Fan, made from a $1.99 motor and some 3D Printed Parts is producing 12 grams of thrust! That's shocking! In this test i'm running the motor at 3.6 volts, slightly above its design spec. The Fan and motor weigh 24 grams, so it producing half it own weigh in thrust.
I wonder what would happen if I swapped this basic 130 size motor for one of the models design for high speeds?
You can download the Ducted Fan and the Test Stand from Thingiverse.
Ducted Fan: http://www.thingiverse.com/thing:530911
Test Stand: http://www.thingiverse.com/thing:530914
The FA-130 size motor I used is available on Pololu: www.pololu.com/product/77