I have bought underpriced Grill Motor like this: https://www.amazon.de/-/en/GAESHOW-Barbecue-Rotator-Electric-Accessories/dp/B08G89PRPF
And I had an idea to use it in this manner: https://www.deviantart.com/fotorofetish/art/The-Nipple-Clamps-Training-Machine-847728657
I just have to figure out the mechanism, what to attach to the motor and how to set it up to make the most of it.
Any ideas welcome, I will keep experimenting in the near future.