Why is frequency response of a servo critial to motion base design? Why is it even required? The fact is, the better the frequency response of the servo, the better performance of the motion base platform.
In the simpliest terms, the motion base must follow the input properly. So if the motion base is to follow the commands from a Host computer in a full-flight simulator, and the pilot response is about 2Hz or less, the motion base needs to have >5˚ at 2Hz of phase shift so that the motion base accurately tracks the signal from the Host Computer flight model. It is required as the phase loss of the motion base affects the stability of the pilot's control loop.
The Engineering Team at Servos & Simulation, Inc., analyzed the performance of one of our motion base designs. The plots for the performance show the maximum position as a function of frequency, the maximum velocities as a function of frequency, and the maximum accelerations as a function of frequency. The servo has an inner rate loop using the encoder on the motor for feedback allowing the servo to have a bandwidth of more than 40 Hz. The outer loop is a position loop with a bandwidth of 4 Hz. The position loop gain is limited by the gain available in the drive amplifier (power amplifier that drives the motor). Servos’ engineers add electronics to the servos and increase the gain by at least a factor of 4 which increases the position loop bandwidth to 16 Hz.