The magnitude of the hybrid parameters of the 3CH and 4CH tele operation systems are shown in Fig. 11. As it can be seen, |h12| is above the 0-dB level for the 3CH case, while it is close to 0 dB in the 4CH case. This is in agreement with the time- domain force profiles in Figs. 6 and 11, where force tracking in the 3CH architecture is not on par with that in the 4CH case. This, however, does not affect free-space position tracking, as illustrated in the |h21| spectra of Fig. 11. As it can be observed, for both cases |h21| spectra are close to 0 dB, showing excellent position tracking for frequencies up to 100 rad/s. As expected from (16), low values of the output admittance (h22) in the 3CH and 4CH architectures show that the movement of the slave in response to external force disturbances quickly converges to zero when the master is locked in motion. With regard to h11, due to the mass of the handle between the force sensor and the operator’s hand, over high frequencies the input impedance h11 = Fh Ym is identified less accurately than the other hybrid parameters. Nonetheless, low values of h11 over low frequencies are evidence of the fact that when the slave is in free space, the user will not experience a force or sticky feel of free-motion movements in the 3CH and 4CH cases, which would have been umdersirable