This instructable features 3D printed propeller blades, with improved performance on the original design (thing:30284) by Landru. Thing 30284 is an awesome design with a pretty clever approach to printing orientation for optimal durability, but unfortunately it failed to provide sufficient lift for my UAV. I've slightly modified his design to give the blades a larger surface area which significantly increased their thrust.

Note: These blades were designed to fit Sky Viper quadcopters such as the v950hd. Once I move on to something more "grown up", I'll upload the designs on the same Thingiverse page.

Step 1: Download and 3D Print

Download the design files:

http://www.thingiverse.com/thing:1060181

3D printer settings:

Supports: No (already included in STL)

Resolution: 0.17mm layer height

Infill: 0.3

Printing the attached STL file will get you a pair of "A" blades. To get a set of the "B" blades I simply set my object's Y-axis scale from "1" to a "-1" before slicing it. Also, don't worry about the support material, as I've already included it in the STL's mesh.

You can set your slicer to whatever settings you prefer, however, I've had most success printing it in ABS plastic from a 0.40mm nozzle at 0.17mm layer height, 30% infill, and a 2-layer shell. My printer's extruder and hotbed temperatures were set at 215 and 112 degrees Celsius. I used a Solidoodle 3 device and its default software Repetier Host.

Step 2: Remove Support Material

When creating 3D-printable objects, there are two ways to add support material to prevent your object from turning into a stringy mess mid-print. The first way is to use automatic feature of your STL file slicing software, and the second way is to add in the support structure manually.

I found that the optional automatically generated support material was difficult to remove and deformed the propellers too much, so I manually designed and included the support material in the STL file. So, all you have to do is throw the STL into your favorite slicing software (I used Slic3r), ensure that your printer is all set to print without supports, then print the blades, and pull the support material off.

You'll need:

Four 3D printed propellers with support still attached
Scissors
Razor blade tool

After cutting off the excess base support material, carefully remove the rest of the support material with a little bit of help from a razor blade tool.

Step 3: Cold Acetone Vapor Treatment

The layer separation is the largest drawback of the RepRap 3D printing technology, which is why it's important to perform this additional step before you can safely and effectively use these props on your quadcopter/UAV. This next step ensures that the layers don't separate mid-flight.

The acetone vapor deposits on the surface of the 3D printed object, fuses the layers further, and gives it a smooth glossy finish. It's highly recommended not to skip this step.

You'll need:

Acetone
Large glass bowl (holds the acetone vapor in)
A sheet of glass (optional, but recommended)
Two or three paper towels (12x12in or 30x30cm) folded as shown
Magnets or other means of attaching paper towels to the inside of the chamber

It's best to suspend the blades on their side, as shown on the image, in order to ensure even vapor distribution along the entire surface of the blades. I use a flat sheet of glass as the floor of the chamber, and a 12in (30cm) diameter glass bowl as the container.

Attach two folded paper towels via neodymium magnets (see the photo above) to the walls of the chamber
Pour enough acetone on them to soak them (~10 tablespoons)
Quickly cover the chamber over the blades (Acetone evaporates fast)
After 25-30 minutes (no more than 35, or the blades will deform or melt) remove the chamber
Let the blades sit for a minimum of 3-4 hours (use a small fan)

Note 1: Make sure to cover the chamber immediately to avoid inhaling acetone vapor or causing an explosion. Yes, acetone vapor can ignite and is toxic, so do not work next to an open flame and do this step in a well-ventilated space.

Note 2: After removal of the acetone chamber lid/bowl, avoid touching the blades, because the vapor treatment makes the blades very soft, and so during the drying/curing period the blades can be easily deformed if mishandled. Deformed blades will decrease flight performance. It's also very helpful to use a small fan to accelerate the drying/curing process.

Step 4: Balancing

After the curing/drying is done, you can remove some material from one or the other side of each propeller in order to balance it.

You'll need:

3D printed propeller (glossy or not)
Screw driver (or more precise propeller balancing equipment)
Razor tool

Doing this is also highly recommended. Balancing reduces vibration, improves the prop's performance, and will improve your drone's battery and motor life.

Insert the screw driver into the propeller's center hole to see which side is heavier.
Remove some material by scraping the upside (not the underside, for best aerodynamics) edges of the propeller.

If balancing is done right, the center of mass for the propeller will be as close to the middle as possible.

Step 5: Install the Propellers

After balancing is completed, it's important to install the blades in a proper configuration. The above image shows the proper way to do it. The "A" blades go on top right and bottom left, and the "B" blades go on top left and bottom right.

Step 6: Fly!

After ensuring the blades are firmly attached to your UAV, it's time to go for a test flight!

If it fails to take off, make sure the previous step is completed properly and the "A" and "B" blades are installed in a proper position. If you notice too much vibration, your blades need a bit more balancing.

As shown on the above test flight video, it should fly with absolutely no issues, and the blades should work almost as good as the stock ones.

Have fun and make sure to follow standard UAV flight safety procedures!