Abstract— Working in the dynamic environment makes the operation of excavator arm be affected by many factors. This leads to the unexpected operation of the automated arm. In order to overcome this problem, in this paper a robust adaptive controller that does not depend on the system parameters is presented for an excavator arm. Firstly, the model of the excavator arm is demonstrated in the Euler-Lagrange form considering with overall excavator system. Next, a robust adaptive controller has been constructed from information of state error to calculate the unknown factors. In this paper, the stability of overall system as well as the convergence of the adaptive components is mathematically proven by using Lyapunov stability theory. Also, the proposed controller is model free then the closed loop system is not affected by disturbances and uncertainties. Finally, the simulation is executed in Matlab/Simulink to compare the performances of the presented scheme and the PD controller under some conditions (i. e. no load, full load, rated parameters, varying parameters). The simulation results show that the proposed algorithm given the better performances (fast response, small steady state error) for all cases.