Abstract: The armature of the model electric locomotive motor is connected as one arm of a bridge circuit having a D.C. supply voltage. When the armature is held to prevent rotation, the bridge is balanced by means of resistors in the other arms so that no voltage appears across the output. When the armature then rotates the voltage across the bridge output is the back EMF produced by the rotation of the armature. A variable reference voltage obtained from the same D.C. power source is introduced opposing the back EMF and the resultant is used to control the current between the power supply and the bridge. The armature back EMF is thereby held by the bridge balance essentially equal to the reference voltage and if a heavy load is applied to the armature shaft the resultant bridge unbalance will retain the desired armature rotational speed constant irrespective of load changes, but variable directly with the applied reference voltage.

Abstract: At least two coil spring rotational mode reverberation lines having transducers at two remote ends thereof are coupled in cascade circuit by means of intermediate long wire transverse mode line structure. Thus, two (or more) coils may be located side by side with a long thin wire coupling opposite ends of the coils, thereby considerably reducing packaging size of long time delay reverberation lines, and producing coupling means that is less susceptible to physical shock. The wire comprises universal type coupling means for coupling together coils of different characteristics.