https://www.youtube.com/watch?v=GLzZMUE9Gac Designed, 3D printed, assembled and tested in under one hour, "Simple Ball Bearing Car" uses a 3D printed single piece chassis with four neodymium magnets (6.35mm diameter by 1.6mm thick, used for the axles) and four ball bearings (14.5mm or 9/16" diameter, used for the wheels) to create a simple to print and assemble car that rolls quite far on smooth surfaces. It's a fun "first 3D printed" project that the kids and grandkids can help print and assemble (but please see "One final note, ..." below). I 3D printed my chassis at .2mm layer height with 20% infill and no supports which completed in around 25 minutes. Next, using slip joint pliers, I pressed the four neodymium magnets into the magnet sockets in the chassis. Finally, I connected the four ball bearings (one each) to each of the four neodymium magnets and it was ready to roll! On a smooth wood floor, this model will coast 30 feet and further. One final note, the neodymium magnets are small and the ball bearings easily separate from the chassis, so please use caution around the younger kids and grandkids (e.g. no eating the car parts !). Designed using Autodesk Fusion 360, sliced using Cura 4.1, and printed in PLA on an Ultimaker 2+ Extended and an Ultimaker 3 Extended.