Modern robot control methods require knowledge of the form and coefficients of the joint friction. The main feature of the present work is the practical application of the nonlinear filtering approach of Detchmendy and Sridhar, on both computer simulation and experimental data, in frictional identification. The results confirm the feasibility of the proposed estimation approach. In addition, different models of friction have been examined for the estimation of Coulomb and viscous coefficients. In these models, asymmetry of the parameters, as an essential assumption, has been investigated and separate values determined for positive and negative directions of rotation. The experimental results justify the introduction of asymmetry, particularly for the Coulomb coefficient. It is shown that an asymmetric Coulomb and viscous frictional model is appropriate for the DC servo motor investigated. The quality of the fit of the coefficients was measured in terms of the RMS torque error, and low torque errors has been obtained.