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](https://www.thingiverse.com/thing:5337071) 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](https://www.nablu.com/2022/03/whose-hands-are-biggest-you-may-be.html)).
* 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](https://www.nablu.com/2022/03/elliptical-blade-naca-airfoil-propeller.h