Simple three-gimbal gyroscope toy.
Print one of each gimbal, the frame, the base, the rotor and axle. Assemble, squeezing gimbal rings orthorgonally to allow insertion of the next smallest. The axle needs to be printed with some care, maybe cleaned-up and balanced by gentle heating and pressing into the best possible balance with the rotor.
SCAD source is included for tweaking. I added the pin_extra hack to tighten the gimbal pivots by 250 um over exactly the right size as my printer would print them slightly undersized. It is also easier to file/sand the pins to get the best fit if you start with one a bit over-sized.
I'll add a motorised rotor eventually.