Pinewood Derby Racer

thingiverse

Here's my pinewood derby racer, fresh from several recent wins. Design: I carved out the body and built the back "window" to hold standard 1/4 OZ wheel weights you can buy at Harbor Freight Tools. As it sits, it weighs exactly 5.000 OZ with a balance point of 1" in front of the rear axle. The wheelbase is longer than an original Drill pinewood derby car, but the width and length are the same, keeping it within regulation. I didn't conduct any wind tunnel tests to show that the rear wing actually does anything; I simply built this car to showcase a modern take on a 100-year-old tradition. Let's be honest, wings look cool! BUT...I did camber the axle mounts and design it so the 50/50 balance point is exactly 1" in front of the rear axle. Build: I printed it using ABS, but that wasn't necessary; PLA would have been just fine. What I DID do was coat my heated bed with goo. I mixed up a thick layer of acetone and ABS to create an INSANELY smooth surface on the bottom to assist in aerodynamics. Which is absolutely hilarious because AFTER I printed it, I realized I forgot to notch out a weight location on the bottom, so anything the smooth bottom did to help, the low hanging weights ruined. :D Since I used 0.2mm resolution, it LOOKS like it has grooves at the top that would ruin aerodynamics, but as you can see in the side shots, the top is smooth as glass. What I learned: • Don't be in a rush! This was a last-minute idea two days before our derby; I forgot to notch out the bottom for weights. Could have been more aerodynamic. • Make the axle holes a tiny bit bigger; I made them smaller to make sure they fit tight. The axles fit, but it was a hard press, and you can see the stress on the plastic bottom. • Redesign top of rails for the rear wing; they fit well, but I think they look a little funny because they're not completely flat to the bottom of the wing. I was looking at my track car when I designed it, and my track car wing is held up by 4 nubs off the wing rails so I designed it the same. Looks good on a real car, funny on a pinewood derby car. • The future design will have small nubs where axles mount to make sure wheels are safely away from the body; they don't rub, but I'd feel better. Post-Production: Use acetone to keep the wing together; held up great even after a flying off the track incident! Results: Not 1st place but held my own with the top 10 cars. As a parent, I wasn't actually placed, but I would have been in the top 5. I had an alignment issue after it flew off the track so it slowed down dramatically. Easy build, fun design; I do plan on improving on this! As always, design files are available to those who'd like to build on this. Entirely designed through 123D so if you don't use that, I can't help you. Print Settings Printer: Prusa i3 Rafts: No Supports: No Resolution: 0.2 Infill: 20% Notes: Supports don't matter for my printer but there are axle holes if you want to use supports. You know your printer best. Large flat pieces so I didn't use rafts. Also, I used a goo mix of ABS and acetone to smooth out the bottom; that eliminates the need for rafts on my printer. 20% infill is more than enough for this. Post-Printing Step 1: Sand the stop to smooth it out