I have recreated a 3D printed robot which can adjust its height to fit into tight spaces and even crawl under (some) doors. Here is a video showing my recreation in action:
https://youtu.be/722XO0xlWLE

This robot is based on an existing design (called “STAR”) from a 2013 research paper. That design comes from David Zarrouk, Andrew Pullin, Nick Kohut and Ronald Fearing at the Biomimetic Millisystems Lab, UC Berkeley. Here is a link to the original paper on this robot: https://people.eecs.berkeley.edu/~ronf/PAPERS/dzarrouk-sprawl-icra13.pdf

A link to the Thingiverse page is above, which has the 3D printing files, a BOM, the Arduino sketch used, and more.