Al Bencomo has created this wonderful 3D-printed robot that can overcome obstacles by changing the shape of its wheels. FRILLER (FRILL Explorer Robot) uses a Raspberry Pi 3 with Android Things OS to control motors connected via an Adafruit Motor HAT. As Al explains it:
The wheel deformation mechanism is composed of two DC geared motors, sliding racks, and an elastic cord. When the motors push out the racks, the wheel diameter becomes larger. The elastic cord around the wheels assists with the return of the spikes to the close position when the motors pull the racks back inside. The wheels remain round for faster travel on roads or indoors, but transform into spikes to overcome obstacles off-road.
You can read more and download the STL files for the 3D printer here and view his code on GitHub here. See it in action in the video below: