5.3.3 Pointing/Motor Control

The sat-nms RMC performs the pointing / motor control as a closed control loop, independently for each axis. If the measured position value differs from the target value, the motor is activated to compensate this difference. It makes no difference if a new target value has been commanded or if the antenna has moved a little bit due to a squall.

Hysteresis

To avoid that the motor is switched forth and back all the time, the ACU tolerates small differences between measured and target value within a hysteresis value. This hysteresis is individually configurable for each axis at the Setup page. To ensure that the motor stands still when the target position is reached, twice the resolution (step size) of the position sensor / encoder must be set. Common values are:

If the motor control loop still oscillates with the recommended hysteresis values, this is due to the off-carriage of the antenna drive. Either turn down the motor speed at the motor driver unit or enlarge the hysteresis value in this case.

Motor drive signals

The sat-nms RMC provides a number of output signals to control a motor driver unit. These signals (they are available for all two axes) are:

• FWD --- This signal switches the motor on for the forward direction.
• REV --- This signal switches the motor on for the reverse direction.
• FAULT --- The RMC monitors this signal all the time. The signal is high active, i.e. the RMC expects no current flowing through the optocoupler while teh the drive is OK. If the circuit is closed, the RMC signals a fault and stops the motor.

Very important is how the direction of movement is wired. The proper direction depends on if the antenna is operated on the northern or on the southern hemisphere:

Look 'through the antenna' to the sky for the correct orientation of the left/right/clockwise directions. The sense of the position sensors must set that the sensors give increasing values while the antenna moves FWD.