The existing commercial rotators usually have either AC motors or DC motors, according to
this review and this list. Also in SatNOGS Network, until today, they are 39 ground stations with rotator. Almost the 90% are Yaesu G5500. An average number of observations per day for one station are:
- in 1h, at least 2 observations of 15min each
- in 15000 hours, 30000 observations
- which means almost 2 years
So all the system (mechanical and controller) must achieve a large MTBF.
The mechanical failures, if the antennas are balanced and the rotator isn’t working in extreme environmental conditions, are limited. The most usual failures are done in controller due to electromechanical switches (relays).
In order to replace the commercial controller must be developed either 2 different controllers for AC and DC motors or an universal controller for both types of motors.
The existing documented solutions for DC motors are:
- SatNOGS controller with modified motor driver in order to drive bigger DC motors.
- SARCROT, that you can select the driver according to DC motor power.
The existing documented solutions for AC motors are:
As described in this application note the use of triacs and conduction angle control
is low efficient and introduce harmonics (which in our application are in low frequencies).
Another method to control an AC motor is to use an inverter. The input voltage of the system would be low voltage DC. The system would be consist of a H-bridge that driven by SPWM
in order to produce a variable frequency sine, by using a filter in the output of the H-bridge. The same circuit could be used to drive DC motors by using PWM to drive the H-bridge.
A simplified QUCS simulation is presented,
For simplicity are used switches instead of mosfets.
The output of H-bridge: