I was discussing gyroscopic forces and angular momentum with my two boys when they were 7 and 9. I wanted to give them a cool demonstration, and give them a toy with which they can experiment to help grasp the concept. So we sat down together and designed this. They have been having fun with it all afternoon, and I will admit... so have I.

Here is a video of it in action:

I have included the STL's, and other CAD formats (native Solidworks 2018, STEP, Fusion360 import). Feel free to modify, remix, etc. Have fun.

Parts Required:
Printed Parts (I have plated the STL's for easy printing)
Qty:2 - 608 Skate Bearings (low friction bearing like what were used in old fidget spinners work best)
Qty:21 - 3/8" Hex nuts to act as flywheel mass (let me know if you want one for metric hardware as the weights)
Qty:1 - 3mm x 45mm long bolt
Qty:1 - 3mm hex nylock nut
Optional: A few 3mm washers to space out the sides if center rubs