I thought it would be fun to design a pullcopter toy with over-engineered features, that is, interesting improvements that aren't necessary for the function of the device, but may (or may not) improve the performance. This design makes use of three of my other designs:

• Tilted-sinewave gear cutting
• Ergonomic handle
• Elliptical-blade NACA airfoil propeller

The over-engineered improvements include:

• Designed to assemble without tools or fasteners. The handle assembly snaps together.
• Ergonomic handle based on actual anthropometric measurements of human populations, described and cited [in my blog article about building the handle]( https://www.nablu.com/2022/03/whose-hands-are-biggest-you-may-be.html). The handle can also have finger grooves, but I don't recommend this because then it fits only one specific hand size (see below).
• Custom-cut gear using asymmetrical gear teeth (smooth sawtooth using a skewed sinewave profile). The idea here is that the forces on the gear teeth are just one-way, so eliminating the symmetry decreases the pressure angle of both meshing teeth, and increases the strength of the tooth in the force direction. However, this may actually be a compromise because asymmetric teeth seem to have more rubbing than rolling surfaces, increasing the wear. The two parts using these gear teeth are small and easy to re-print.
• The propeller design is described in my blog article about elliptical-blade propellers. The propeller here has a number of improvements over the usual pull-copter propeller:
  • The blades are accurately twisted for constant pitch along the length of the blade.
  • The 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.
  • Elliptical wings are considered to be efficient, and the propeller blades have an elliptical profile (albeit the ellipse is truncated at the blade tip, and highly distorted toward the blade root).
  • The blades are swept to reduce leading-edge drag. Ideally they should be swept forward to help 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.
• Two paths for the pullcord, for pulling it with the left hand or right hand.
• Tapered propeller drive cogs allow the propeller to depart in a range of vertical speeds.

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 119.

If you have unusually large hands, or if you decide you want finger grooves in the handle, you need to set the handlength and handwidth parameters to your own personal measurements. You can set the parameter handle_fingergrooves to true once you set your hand measurements.

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