Back in 2006-2007, a dynamically-stable robot named TBot was developed at the Florida Institute for Human and Machine Cognition (IHMC) by a team of professional roboticists. Financed by a now-defunct DARPA program, the goal was to create a a robot capable of fast transportation in open areas and precision operation in tight urban combat scenarios. Using two "arms" capped with an extra set of wheels and a linear "waist" actuator, TBot can transform from various four-wheel statically-stable (large footprint) configurations to a two-wheel dynamically-stable (small footprint) configuration, and vice-versa. I'm still a bit skeptical about dynamic stability -- often, it seems to add many challenges for very few added benefits. Perhaps the transformer approach, like the TBot and the iBot personal wheelchair, is a healthy compromise for those who insist on (occasional) dynamic stability?
Credit for the TBot (and its prototypes) goes to the IHMC team: Tim Hutcheson, Victor Ragusila, Shervin Emami, Jerry Pratt, Peter Neuhaus, John Rebula, Ryan Chilton, John Carff, and Chris Wilmer.
A few videos of TBot and its early prototypes (other videos):
Here is what Shervin Emami (TBot team member) had to say:
The Tbot project was funded by the US Military (DARPA) to test different types of robot soldiers that could replace human US soldiers in Iraq and Afghanistan, where large tanks are too bulky to fight in the inner city buildings. The heads of DARPA liked Jerry Pratt's idea of trying a tall robot that can balance on 2-wheels (therefore fit in tight urban spaces) while carrying a camera or gun at roughly eye-level of a human. These are difficult tasks to obtain from a traditional 4-wheeled robot, and since 2-legged bipedal walking robots were too complex, balancing on 2-wheels was a good compromise.
There was also interest in having the balancing robot drive over rugged terrain and obstacles, handle large falls and possibly climb stairs -- potentially driving anywhere in a typical urban house, including staircases. There was also the possibility of using the arms to help drive over obstacles much larger than a 4-wheeled vehicle could handle. Allowing the balancing robot to reconfigure itself into a low-lying 4-wheeled car was also desirable for the military since it would be more difficult to see or hit the robot while allowing it to drive fast like a car. So the Tbot was born!
[Thanks to Hizook reader Shervin Emami for his assistance on this post.]