Understanding Davies Method's kinematic analysis
When performing Davies Method, we use the origin of the system as a reference for kinematic calculations. Once we compute the effect of a joint into a link, it is computed as if the link virtually extended to the origin. So we compute the kinematic of a point in the link virtually positioned when the whole link suffers the kinematic effects caused by the joint movement.
As Davies Method deals with Closed Kinematic Chain System by conception, the Kirchhoff Voltage Law applied using Graph Theory generates an equation for a Closed Kinematic Chain. So we compute all the joint contribution to the kinematics of the origin and, as the circuit is closed, we begin at the origin an end at the origin, obtaining a net velocity of zero. Thats how one kinematic equation is born in Davies Method.
The use of Kirchhoff Voltage Law in a Graph framework allows us to get unambiguous equations.