I wrote in a previous post about my first attempt at designing a pull-back racer. Being the over-engineered design it was, I took a shot at simplifying it for use in workshops and educational purposes.
I removed the vast majority of the pressure-fit components, and reduced them to 3. It isn’t nearly as elegant to the eye, but it is far easier for kids to assemble. There is the base that holds the elastic in place, and the sides to hold the axles.
I went with skewers for the axles, and the wheels can be laser cut as well, or cut from dowel. In the pictures below, they are laser cut.
Overall assembly is pretty straightforward: push the sides onto the base, slide the axles through the holes in the sides, add the wheels, and strap on the elastic. The elastic then needs to be taped to the rear axle so it can wind up around it and provide the drive for the car. The rear wheels, ideally, should pressure-fit onto the axle as well, but often they don’t, and this is a trade-off for using skewers. Skewers tend to vary in diameter significantly, so while sometimes they will pressure-fit well, other skewers from the same pack may be way too small. It is nothing a little bit of masking tape can’t fix.
Different sized wheels can also be cut and swapped out so kids can experiment with the effect of wheel size on the car. You can also add elastics around the outside of the wheels, or tape, or foam tape, to experiment with the effect of friction on the car’s wheels and its overall performance.
I have been working on removing the elastic and replacing it with a 3D printed spring, so that kids can be exposed to differing kinds of modern manufacturing (additive manufacturing with 3D printing and subtractive manufacturing with laser cutting). This will also remove another fiddly bit to the project: taping the elastic to the rear axle. It doesn’t always work out on the first try, not that is a bad thing, it’s good to have a deliberate failure point in a project so you can create a learning opportunity out of it, but sometimes, due to circumstances, having a fail-proof project is beneficial as well.