You may recall Justin, the humanoid robot sporting two DLR-III lightweight arms and two DLR-II hands. Well, Justin has recently acquired a 4-wheel mobile base dubbed "Rollin' Justin". The base utilizes a "powered-caster" design similar to the Willow Garage PR2, except that the torso-caster linkage contains a spring-loaded lift mechanism that gives the base a variable footprint. I'm sure this will prove useful when trying to squeeze through doors, adapting to uneven terrain, or providing a larger support polygon. While we currently do not have any video of the system in action, there are a number of great pictures and design documents below.
First, let's take a peek at some pictures of the physical system, which apparently debuted at Automatica 2008. These pictures come from Paolo Robuffo Giordano's website, a presentation by Ian Howard, and emails with Christoph Borst.
Like I mentioned, this system has a variable footprint that is accomplished by independent, spring-loaded lift mechanisms on the linkages between the "powered-casters" and the robot "torso". You can see this in the CAD drawings below. On the left is the "final" design, from the DLR handout. The image on the right comes from an earlier prototype design document.
The footprint can be varied as shown in the image below.
I'll be curious to see the videos of "Rollin' Justin" in action. I've been assured that such videos are forthcoming in the next few months (awaiting peer-review decisions). I'll be sure to post them when they're made available -- but in the meantime, let me know (in the comments) if you have any other information about this base.