Pinewood derby (slow but great lessons learned)

thingiverse

I had an absolute blast participating in this fundraiser at work. This was my attempt at a pinewood derby car, and I'm proud to say it was a real learning experience! The truth is, it was slower than molasses - but that's okay, because I learned some valuable lessons along the way. One thing I discovered is that bearings may sound great on paper, but in reality, they can create a ton of drag. On the other hand, the rest of my car design worked really well. If I were to do it all over again, I'd definitely redesign the car to ditch the bearings and maybe even use a small pin or something similar instead. Additionally, the frame wasn't stiff enough to keep the smaller wheel off the ground, which was a major problem. To build this baby, I used 3/16 rods that I cut to length for the axles, some high-tech RC car bearings, lead shot as ballast, and even a magnet in the front (I thought the gate would be made of iron, but it wasn't). If you're interested in learning more about pinewood derby dynamics, I highly recommend checking out this great tech paper here: https://www.mech-sci.net/3/73/2012/ms-3-73-2012.pdf (not written by me, unfortunately!). Here are the key takeaways: * To get the best results, your car's center of gravity needs to be as low as possible and positioned towards the rear. I learned that using tungsten can help with this, but it's way too expensive - lead shot is a much cheaper alternative. * The overall weight of the car should be just right, not too heavy or too light. According to pinewood derby rules, we're pretty much maxed out on weight. * Wheels need to have as small a second moment of inertia as possible (basically, the weight in the wheel should be close to the spinning axis). A spinning CD is way better than a spinning wedding ring, even if they weigh the same! * We want to minimize friction wherever we can - three wheels touching versus four, polished axles, perfect holes, no rubbing wheel on chassis, Teflon spacers on wheels... you get the idea. * Alignment-wise, it's theoretically best to go straight, but most people end up tracking their vehicles slightly to one side. Maybe a better approach would be to tighten the track width just a bit more than the track itself. And then there are some "cheats" that people use - depending on who you ask, of course! One example is using a sticky nose on the gate (which pulls the vehicle forward).