While the STAR, or Sprawl Turned Autonomous Robot, is more than capable of traveling over obstacles with its three-pointed wheels, it can also make itself thin enough to simply slide under others as needed. This clever design uses an Arduino Pro Mini for control, and normally moves around like a tank, rolling on six wheels that are turned by two motors.

When the task calls for it to go under something, a third motor cranks these wheels to nearly parallel with the floor, shrinking the robot down to a very slim profile—so thin, in fact, that it can actually slide under a door as seen in the video below! 

Print files and more information on the build can be found here, while the original paper upon which this robot is based is also available.