When you use force feedback, you get the feeling that you are doing the
manipulation yourself. This can only be done well if the time delay is
short, on the order of a few milliseconds, up to about maybe 20. Radio
links have time delays not only from time of flight of the signal but
also from the filters used in the transmit and receive electronics. I
worked with 5 mSeconds time delay and 1mS servo loop time and got
decent results. Some time delay is due to the kinematic transformations
done by the control computers. Reliability also suffers if you have to
maintain a radio link between the operator and the robot.