Dynamic Modular Locomotion systems - Rollerblading Robot

Kinematic analysis may not be sufficient to analyse some kinds of modular locomotion systems. In particular, the addition of passive wheeled modules results in the system having more complex dynamics. We are presently examining the analysis and gait generation for such dynamic systems. Systems that we study are characterized by the presence of multiple nonholonomic constraints. An example of such a system is the Rollerblader shown in the picture below.

The Rollerblader is a robot with a central platform mounted on omnidirectional casters and two 3 degree of freedom legs. A passive rollerblading wheel is attached to the end of each leg. The wheels give rise to nonholonomic constraints acting on the robot. The legs can be picked up and placed back on the ground allowing a combination of skating and walking gaits. In [1] and [2], we presented theoretical and experimental results for gait generation for the Rollerblader.

Systems like the Rollerblader, i.e. systems acted upon by a number of nonholonomic constraint, are characterized by the presence of generalized momenta that represent the motion of the robot along a set of unconstrained directions. The use of the generalized momenta terms greatly simplifies the analysis of such dynamic systems. The systems can now be expressed in a reduced form using a nonholonomic connection and an equation describing the evolution of the generalized momenta. The fiber directions for the system represent the net motion of the robot body, e.g in 2 dimensions the fiber directions are given by elements in SE(2). The shape motions for the system represent the internal motions of the individual modules. Now, the nonholonomic connection essentially relates the fiber velocity of the system to the generalized momenta and the shape inputs of the system. More details on the derivation of the dynamics of the Rollerblader and the experimental and simulated generation of gaits can be found in the papers listed below.

Movies

1. Forward Motion Gait : Forward motion gait for the robot where the legs execute a symmetric gait. The legs of the robot maintain contact with the ground throughout this gait.
2. Rotary Motion Gait : Rotary motion gait for the robot where the legs execute an anti-symmetric gait. The legs of the robot maintain contact with the ground throughout this gait.
3. Rollerblading Gait : The legs of the robot make and break contact with the ground alternately.

Relevant publications

1. Sachin Chitta, Frederik Heger and Vijay Kumar, "Dynamics and Gait Control of a Rollerblading Robot ", in Proceedings of the IEEE International Conference on Robotics and Automation, New Orleans, 2004. (PDF)

2. Sachin Chitta and Vijay Kumar, "Dynamics and generation of gaits for a planar Rollerblader", in Proceedings of the IEEE/RSJ International Conference on Intelligent Robots and Systems, Las Vegas, 2003. (PDF)