An earth excavator including apparatus for stabilizing performance by compensating for changes in temperature. The apparatus includes a temperature compensating voltage regulator for regulating and controlling the output voltage of an exciting generator as a function of sensed temperature. The exciting generator supplies field excitation voltage and current to electric motors in the earth excavator. In order to maintain substantially constant current through the motor field windings with variations in temperature of the windings, and therefore to maintain the performance of the motors and thus of the excavator substantially constant with variations in temperature, the exciting generator output voltage is regulated in a manner such that the regulated voltage supplied by the exciting generator is a direct function of the temperature of the motor field windings. The output voltage of the exciting generator is controlled by controlling the average current through the exciting generator field winding. In order to produce a signal representative of motor field winding temperature, the temperature of a representative motor field winding, or of the exciting generator field winding, or of an element having a temperature which is representative of motor field winding temperature is sensed.