Progress 23/03/09

Hi all,

My masters project is based on implementing stability models in the Robocup simulator, and enhancing the best performing model. With the aim of greatly improving the stability, enabling us to perform better in both the German open and the world cup at the end of June.

One of the models I am implementing is the use of angular momentum as described by Goswami et al [1].

The two main parts in implementing this model is firstly; to calculate the rate of change of angular momentum (Hg). Secondly to implement one of three control strategies as proposed by Goswami et al [1].

With the help of Sander we have completed the first part implemented by a new behavior, petersBehavior. Which is a modified version of the Walk behavior.

Briefly explaining the concept of calculating the angular momentum (Which in our case, using the equation obtained from [1] Part 4 section C) involves the rate of change of centroid angular momentum of a robot. When the value of Hg = 0 the robot is said to be stable. The three vectors used to calculate are: GP*R = Hg. Where G is the the Center of Mass COM (obtained via the libats getCOM() method), P is the Center of Pressure COP with R being the Ground Reaction Force GRF.

Within the petersBehavior are three addition files used to calculate the COP (COP.cc), GRF (GRF.cc) and Hg (RANGMOM.cc) as per the coding of the libbats coding system. As mentioned above the COM is retrived via the getCOM() method. The folder and files have been added to the SVN.

The next step is to test the angular momentum in various conditions and then to implement one of the three control strategies. Which should be completed in time before we have a test match with another university just before the German open.

I will post more details in the coming weeks. I have put more details on calculating the COP/COM/GRF in the comments in the code or it can be seen in the paper [1].

Regards,

Peter Snow
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[1] A. Goswami, V. Kallem. Rate of change of angular momentum and balance maintenance of biped robots. Proceeding of the 2004 IEEE International Conference on Robotics & Automation. April 2004