It is necessary to compute binding forces in dynamic simulation of a linked mechanism interacting with an environment, since the constraints change frequently. An efficient solution method is also required especially for the mechanism with many degrees of freedom. This paper deals with a legged robot. Equations of motion and constraints are formulated and their efficient solution method is proposed. Then it is applied to the three dimensional dynamic simulation of the locomotion of a quadpod robot as an example.
The method is executed in the following two steps: The first computes link accelerations and joint binding forces as functions of the binding forces of the first joint for each leg independently, using leg equations. The second determines body accelerations and the binding forces of the first joints using body related equations. Since the entire process is divided into several subprocess, some of them are executable parallel and the dimension of equations solved at a time becomes small.
Two schemes of simulation are also proposed. One specifies the motion of a robot by the joint angles. The other does by the joint torques. This paper deals mainly with the former and discusses a statically indeterminate problem concerning the reaction forces from the ground. An elastic model of the ground with friction is proposed to resolve the problem. Since friction makes equations nonlinear, an iteration method is used to solve it where slippage is detected by aproximation. As for the latter, it is pointed out that slippage and collision problems are unavoidable and left as a future work.
The proposed methods are general enough for the application to a linked mechanism besides a legged robot.

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