Review of Commercial Rotator

From SatNOGS


The existing rotator controllers are old fashioned and use obsolete technology either in hardware or in software. Almost all the motor drivers are based in electromechanical switches like relays. This introduce in a system a limit of how usual could be used for an observation of a satellite and also in accuracy in movements of the rotator. In this review, it is presented the most popular in HAM community, rotator systems.

Existing commercial rotator systems: There are three rotator systems, as i searched, are the most popular in HAM community for tracking satellites.

Yaesu G-5500


Yaesu G-5500, it is an AZ/EL rotator. From data sheet, could understand that it has AC motors (26V@2.8A, specifications of transformer for both motors), potentiometer (isn't multiturn) for position feedback which are operated in +6V, and all control loop is implemented with analog IC's (comparators and op amps). Also the system has end-stops in both axis in both directions (min-max), that immediately cut off the current of motors. The connection with a client is implemented via a rotator interface for example an ardushield that runs k3ng rotator firmware. The cost of all system is ~750$ with analog controller.

Useful links:

Yaesu G5500 - Controller


The gear box of rotator it is a spur gear box. Almost all the gears are made from laser cut sheet metal and the output gear is a stack of laser cut sheet metal gears. Another interesting thing is the brake system that it's a torsional spring in motor axis that blocks the movement from output to input. When a torque applied from output to input the torsional spring "opens" and block the rotation. A mechanical fail of one bracket that mounts the pins of gears are done in station 6 after a lot of observations (oval hole). This problem is produced because the antennas are back mounted without counter balance.

Alternative Rotator Controllers

A list of available digital controllers:

SPID rotators

This company it has two AZ/EL models:


Both of models are using DC motors, according to data-sheets, BIG-RAS and RAS. The power consumption for both rotators is , 12V@6-10A or 18V@6-11A. For position sensor, a reed switch is used, one in each axis. This sensor is mounted in the first stage of worm gear box (in total two worm gear boxes), with total 6 magnets that produce pulses with Vp-p according to Vcc of reed switch.

It seems that the encoder is relative, so when the system starts it programmed the zero position. When the system lose the power, the rotator controller knows the last position, it stores the last position in a non-volatile memory. Also the system has two hard stops in elevation axis that limits the rotation between 0-180 deg. This switches immediately cut off the current to elevation motor. In the azimuth there is no end-stop.

RAS, end-stops in elevation axis

The default rotator controller is Rot2Prog, the motor driver again, it consist of relays. The interface with client is done with [Hamlib]( via a USB. A note here, is the cable is USB-A male to USB-A male, that is weird. Two rectifier bridges used for protection of the board from the currents of DC motors. The cost of Rot2Prog is ~250$.

RAS, Default rotator controller

The datasheet of RAS is referred to a parameter MTBF which is the mean time between failures. For rotator controller is 15000 hours @ -5 to +40°C. For a system that is connected to SatNOGS network means:

  • in 1h, at least 2 observations of 15min each
  • in 15000 hours, 30000 observations
  • which means almost 2 years of operation

But how usual the relays are worked?


Both of the rotators are consist of two stages of worm gear box. The second stage (the output) it takes all the loads. In this system the brake mechanism is the two stage worm gear box (big gear ratio and also the lead angle of worm gear). The cost for RAS with Rot2Prog controller is ~1200$, for BIG-RAS with Rot2Prog controller is ~1600$.

Alternative Rotator Controllers

A list of available digital controllers:

  • RT-21 Azimuth/Elevation, Green Heron Engineering LLC, 889$. This feature is nice, "Allows different Azimuth and Elevation rotators from any manufacturer provided they both use either AC or DC motors. (Example: We can configure the Azimuth to use an OR-2800 and the Elevation to use a DC motor linear actuator. OR, the Azimuth to use a T2X, and the Elevation to use a Yaesu G-550)"
  • MD-01/02 HR, it is high resolution edition of rotator controller, with resolution of 0.1875 deg. Instead of using reed switches in first stage of worm gear box, it uses a hall effect sensor. Again the motor driver is electro mechanical switches as shown in picture in the page 3 of data-sheet. This controller, also, support soft-start functionality (PWM control) only when the power supply is higher than 20V, according to this post.

The cost of this controller (only) is calculated:

so the cost of MD-02/HR is ~500E.

SPX rotators

Electronics & Mechanical

A series of AZ/EL rotators:

All of these rotators it seems that are based in the same, first stage, worm gear box with the RAS. The second stage it is like that and changed according to the maximum output load (and maximum break torque). From all the data-sheets seems that motor needs power 12-18V@3-20A or 20-24V@3-20A (max current depends on load or rotator controller, e.g. PWM control). All of these rotator use the same controllers with RAS/BIG-RAS. The motors are DC (it seems that are the same with RAS/BIG-RAS). For position sensor, a reed switch for standard version and a hall effect sensor for high resolution version. From the number of cables and from the type of controller it seems that there no an interface of end-stops connected to rotator controller. This post confirms that the SPX-01 and SPX-02 have no end stop switches on either azimuth or elevation. Also the limits are set in the controller, based on the users cabling setup. In this system the brake system is the double worm gear. In the specification, the rotation range is AZ/EL:360/180deg is the same with the RAS. The available rotator controllers are the same with the SPID rotators.