I have always been fascinated by these exercise gyroscopes and wanted to understand how they work, so I set to make one. After many prototypes it seems the important points are: add enough mass, distribute the mass as far from the rotation axis as possible, ensure there is enough friction so that adding torque transfers energy to the gyro.

Another important point is to ensure there are no sharp edges or bits on the gyro core. RPMs can go well over 9000, so make sure the fast rotating thing is super smooth before firing it up.

The parts to print are: 2 gyro half-cores, 1 case bottom, 1 case top, 1 holding ring and 2 washers. I found the ring and washers noisier if printed in PLA so I recommend PETG for those. And then to assemble it you need 14 M5-20mm bolt screws and 2 M4-20mm bolt screws.

To assemble follow these steps (see the accompanying images):
1 - Screw the M4 bolts. These will serve as axle for the gyro to rotate around
2 - Assemble the gyro core using the M5 bolt screws. Make sure they go in through a large hole and exit through a small hole on the other half.
3 - Add the washers and holding ring, as shown here
4 - Set the gyro core on the bottom part of the case
5 - Close the case with the top part. Done!

You can see how to spin the thing here and here

Enjoy!

Prusa

i3 MK3

No

No

0.2mm

15 - 20%

This thing operates on the friction of the axle as it rolls on the case. Some case materials will work better than others. I found PLA and PETG to be ok but ABS seems to create too much drag.