Way over-engineered pullcopter V4

Only on Thingiverse: The best-flying pullcopter is back!

Here's an update to my pullcopter toy with over-engineered features, that is, interesting improvements that aren't necessary for the function of the device, but may improve performance.

The original over-engineered features include:

• No tools or fasteners needed for assembly! The handle parts snap together.
• Ergonomic handle based on actual anthropometric measurements of human populations (see my blog article about building the handle).
• Custom-cut gear using asymmetrical gear teeth (smooth sawtooth using a skewed sinewave profile) to decrease the pressure angle of the meshing teeth while increasing the strength of the teeth in the force direction.
• The propeller design (described in my blog article about elliptical-blade propellers), has a number of improvements over the usual pull-copter propeller:
  • Blades are accurately twisted for constant pitch along the length of the blade.
  • A blade transitions through three NACA airfoil shapes from the root to the tip: NACA 9440, NACA 6412 (commonly used for propellers), and NACA 3412.
  • High aspect ratio blades for greater efficiency.
  • The blades are swept to reduce leading-edge drag. A forward sweep helps collimate the air-jet directly downward to minimize spread and improve thrust.
  • The propeller ring also uses an airfoil profile, a symmetrical NACA 0020, to reduce drag.
• Are you a lefty? No problem! There are two paths for the pullcord, for pulling it with either hand.
• Tapered propeller drive cogs allow the propeller to depart in a range of vertical speeds.

New features in v4:

• Includes a 4-bladed propeller, observed to have a slightly longer flight duration than the 3-bladed version, but the 3-bladed version appears to reach a higher altitude.
• Includes a propeller with loop-shaped blades as an experiment that you can try, although it takes more material and is heavier so it doesn't go as high but stays in the air a good amount of time. Wear eye protection when flying this! A 2-loop version consistently self-destructed on testing, but the 3-loop version works OK.
• Taller drive gear case for better hand clearance under the propeller.
• Thicker attachment rails on the case for better withstanding of pullcord forces.
• Propeller library improved with minor fixes and support for loop-shaped blades.

Before printing the parts

I recommend you print the "clearance_check" STL or 3MF file first. This is a set of all the parts that need to fit together, truncated for quick printing and checking. If the clearances seem too tight, you may need to adjust them in the pullcopter.scad file. There are four clearance parameters starting at line 133.

Otherwise, see the print settings for each individual part below.