For a pretty good primer on generator operation, try my article on 6 volt generators in the tech tips section. You've got the basic operation down pat. The residual magnetism in the armature induces a little bit of voltage into the field coils, where the "A" circuit generator routes the voltage out of the Field terminal to the regulator. The vibrating-contact regulator points provide the ground for the field current, or insert a resistance into the circuit. The current regulator is in the "Armature" circuit, and carries the full charging current. When charge current is high enough to open the points, the field circuit gets a resistance inserted, because the current regulator points and the voltage regulator points are in series with each other. One or the other, not both at once, control the field current.
For a full-control electronic regulator to work, some type of current sensor would be needed to prevent overloading the armature during low-battery operation. The resistance of the armature is low enough that brush arcing, or overheating of the windings, or both, is possible when the battery resistance is too low to oppose maximum current flow.
Jerry
