This is a buffer or suspension system by spring for a robot or toy cars. The principle is easy, two cylinders, one inside another that allow a relative movement within it, and we add a spring to recover the position when load is not applied.

The small hole in the inner cylinder is to avoid that both cylinders leave the right position if you take the robot or the toy.

Download the .scad file and introduce your parameters.

Generate the .stl file. Or just download the .stl examples files

And print it.