Universal rotator controller

rotator

#1

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:

  • SARCROT, The Mk1c version, which uses triacs to do conduction angle control (thanks @vk2byf).

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:

@Acinonyx, @cshields , @DL4PD, @drid, @csete, @manthos, @pierros thoughts?


#2

So speed control is accomplished by varying the frequency?


#3

Hey @drid!! Yes by variable frequency that produced by SPWM (sine pulse width modulation).


#4

I think that this approach is awesome since it provides us with the opportunity to create a truly universal solution for the vast majority of the rotators out there (including of course the SatNOGS rotator) and would unify the open source (or open source to be) efforts and community around them.

@azisi keep us updated on the tests and practical feasibility!


#5

If you don’t mind I would like to invite Phil Karn, KA9Q, into this thread as I have had a very good conversation in Friedrichshafen about exactly this with him.


#6

Very nice works @azisi :smiley:
Also, the survey you made is very useful :+1:

The idea we have been working with at OZ7SAT is that for AC motors we generate a sine wave using the DAC of a processor and amplify it using an audio amplifier IC. OZ2ABA found some good amplifiers that can be used.


#7

I like the SPWM approach much better because of it is high efficiency. The amplifiers will be losing too much power while the SCRs will be producing a hell of harmonics which will be heating up the motor.