This paper addresses the design of a robust Lyapunov-based controller for flexible-joint electrically driven robots considering to voltage as control input. The proposed approach is related to the key role of electrical subsystem of the motors, thus is free from mechanical subsystem of the actuator dynamics, considered here as unmodeled dynamics. The main contribution of this paper is to prove that the closed-loop system composed by full nonlinear actuated robot dynamics and the proposed controller is BIBO stable, while actuator/link position errors are uniformly ultimately bounded stable in agreement with Lyapunov's direct method in any finite region of the state space. It also forms a constructive and conservative algorithm for suitable choice of gains in PID controller. The analytical studies as well as experimental results produced using MATLAB/SIMULINK external mode control on a flexible-joint electrically driven robot demonstrate high performance of the proposed control schemes.