This balloon helicopter is a neat toy, tool for teaching basic flight physics, and very nice case study in design and experimentation that could be useful in the undergraduate or high school teaching lab.
Notes on flying:
Current best configuration: 16mm blades (blade_16.stl), 13 degree rotor (rotor_13.stl).
Short flying video clip located here: http://youtu.be/mo7PvU1rNRc
Before you build: Unfortunately, it does not yet perform as well as commercial versions, if you are interested in a set of commercial balloon helicopters, consider one of these https://amzn.to/2oTZnuY or this set seemed rather good https://amzn.to/2wW9x1r
Once printed, insert the three blades into the rotor. Insert the nozzle long ways into a balloon and fill the balloon. Insert the nozzle into the rotor while pinching off the balloon, try to ensure that it is straight. Throw. Try different techniques, I found a little spin can help get it going.
Notes on making:
[See instructions for full details] All the components should be printable and all you need in addition is a nice balloon. The helicopter was developed using PLA on one MakerBot Replicator 2, but hopefully you can tell me if it works on yours or others. One key element is the need for a very flat build plate since it requires very thin (0.1mm) films to reduce the weight.
Notes on design:
I really enjoy design for 3D print and this was a nice case study with interesting constraints. I have included the SolidWorks design files for the latest and greatest version. This has gone through 5 major revisions to date in order to get it to fly as well as it does, but it still needs improvement. To get the weight down, I experimented with various surface profiles, wall thicknesses, geometry, build parameters, etc. My hope is others may try to improve it and we can collectively identify the optimal design.
I conducted some basic experiments on variants and have posted STL's for different blades and rotors in case you want to do some of those experiments for yourself. The design files are not well documented but if you have some basic skills with SolidWorks, it should be no problem to figure out.
This design really needs to be made at the highest build quality settings since weight and form are critical. I used 0.1mm layers, 1 shell, 100% fill for the blades and rotor, and switched to 0% fill for the nozzle. All the STL's should already be oriented for best printing. I am also using a glass build plate to ensure a level build platform: http://www.thingiverse.com/thing:57411 and taped with green painters tape. Print and assemble 3 blades with the rotor and if necessary run a bead of glue at the joint to the rotor to reduce leaks. It also helps to hold it together and often blades will come flying out (and possibly hit your neighbours kid - I said sorry). In total the printed parts should weight approximately 11g.
Notes on the blades:
Carefully peel from build plate with flat plaster knife. There is some technique to develop in getting the blades off without warping the film, you have to experiment. Blade STL file names are appended with the outside width of the outlet opening [start with 12].
Notes on rotors:
Rotor file names are appended with the angle of attack [start with 13].
Notes on nozzle:
Do not glue the nozzle to the rotor; instead insert that into the balloon, with the long part going into the balloon. Although it adds to the weight, this feature is there in order to keep the neck of the balloon from twisting shut when torqued by the blades.