This is based on the "Ekobots - Helix generator." by jsirgado. This is a small propeller that will fit directly on a micro motor. It has three blades, but that can easily be changed. The blade direction can be reversed by making the "startAngle" negative. The motor shaft is .8mm in diameter, and each blade is 25mm long.You can use OpenSCAD to customize the propeller and then generate an STL file, and use it to print the propeller. You can also use my STL file.