This CO2-powered crash test car lets you design and iterate crumple zone bumpers in order to protect a passenger egg from injury. Use a CO2 car launcher from someone like Pitsco or Kelvin, wheels from a Lego Technic motorcycle (I got mine on eBay), and create a flat wall for the car to crash into (I put a board against paint cans). The car is guided by monofilament, and I put the wood wall at 50' from the launcher. At that distance, a 12 gram CO2 cartridge will shoot the car fast enough to break an egg without a well-designed crumple zone. Use a slo-motion camera app to capture and analyze the destruction. It's important to not change the bumper posts, just add elements that bend and break in front. If you use Tinkercad, you can search for "Bumper Posts" and then copy and tinker the design, and the posts part will stay locked and in place. The posts are a snug fit in the car chassis. See "CO2-Powered Eggmobile" on YouTube for my 2 min. video : https:youtube.com/watch?v=liyXWWYGgdg&t= .
Printing notes: I print the axles with brim / build plate adhesion, then I use an exacto to make them rounder where they touch the car body and to make the ends fit into the wheels snugly. I also shave the CO2 cartridge opening slightly since the material spreads slightly in the first layer or two. No support is needed to print anything.