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.