I made this a while ago, but never posted it. I had some time to print a track and vertical loop that I thought might make a cool toy for my daughter to play with. She uses 4 balls of different sizes in the video. Anything like a tennis ball should work. The hard plastic ball didn't work as well as the softer ones. We didn't have any matchbox cars to try out, but those might work too!

https://www.youtube.com/watch?v=W7Fc6T-DE1E

This one took a long time to print. 3 of the legs, and 3 of the bases which took several hours each. The loop took the longest and is cut into 3 pieces with 4 connectors pieces total. Glue is helpful if your pieces don't come out perfectly. All were printed on a rep 2 with natural PLA filament.