The folks at the ModLab/GRASP Lab at Penn recently got their PR2 and used the occassion to test out "Mini-PR2". They used $5000 worth of CKBot modules to replicate the degrees of freedom of the real PR2 -- all except the torso. They used 18 modules (14 U-Bar, 4 L7, 4 motor) to create Mini-PR2, and they also added a counter-balance on the shoulder to help balance the arm.
The CKBot modules, which have previously been featured here, enable their lab to try out new ideas quickly and cheaply. In this case, they can use the PR2 simulator to drive their real robot, and they've used an actual PR2 to puppet Mini-PR2 (see 0:49 in video). They are now working on using the Mini-PR2 to puppet the actual PR2.
The CKBot modules don't have the computation power to run ROS on their own, but they can communicate with another computer that translates between the two systems. Their current system listens to the
joint_states topic on the PR2 and translates those messages into CKBot joint angles.