LEGO Derby Car Dimensions

thingiverse

My daughter recently joined a Girl Scouts LEGO Car Derby, and I needed a quick way to check if her car met the size requirements. The contest rules specified certain dimensions for the cars, so I created a tool to determine if they were "legal". The main constraints I considered were the minimum clearance (3/8") and the maximum weight (5 oz). Initially, I designed a simple version of the tool, but during the competition, I noticed that many contestants were violating the rule about a 1/2" flat front nose by using a "forked" design instead. This gave them an unfair advantage, so I modified the original design to include a check for the 1/2" flat front nose. The tool works by verifying if the car extends beyond the front, back, or top of its base, which would make it too large. It also checks if the car can roll smoothly across a center rise without dragging or getting stuck, indicating insufficient wheel clearance. Additionally, it ensures that the car is narrow enough to fit inside the competition box. To determine the weight, I used a scale. I've included the Fusion 360 file for anyone who wants to adjust the dimensions. Simply modify the user parameters, and the model will update automatically.