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RaspberryPi controlled antenna rotator


Current commercial az/el antenna rotators are really expensive(easily over 1500€ with controllers), and moreover technically most are from 90s (analog potentiometer sensors/control, no network, rs/lpt controllable, no web, no rest api, etc).

I tried to take little bit different approach..


  • Cheap common hardware (wormgears, nema steppers, rasberrypi, etc)
  • Intelligence on mast (controlbox includes rasberrypi, this enables many things, like SDR on mast)
  • All digital (digital rotary sensors, steppers, tcp/ip, etc)
  • network (only IO is network, controlling thru different apis(REST, legacy RS emulation api))
  • backward compatibility to legacy software, via software RS (ham radio deluxe, pstrotator, etc)
  • project is only for fun, and learning new stuff!

Project status:

  • hardware & software are in quite good shape

  • Rotator is in test use with 2 x 9el 2M yagis
  • Rotator has survied it first storm, with no damage!
  • Winter has come and rotator still functional even there has been few -20c temperatures
  • Worked over 70 EME contacts on first few weeks after getting amp for 2M.. whole setup seems to work good.
  • 2 days -30c and still working.. bit surprising.


  • Steppers:
    • Common 4-lead NEMA 23
    • one full step 1.8 degrees
    • cheap (from 10$/each)
    • easy to control
  • Worm gears:
    • 90 degree Gearbox ?WormGear Speed Reducer 1:60 ratio

    • most important is ?WormGear, because of that we do not need any brake system!

    • relatively sheap (about 50$ / each)
    • with 1:60 reduction we do not need that much power and precision is 1.8 (from step) / 60 -> 0.03angle /step

  • Absolute rotary encoders:
    • Cheapest used 10bit absolute rotary sensors what i could find (KOYO TRD-3A1024)
    • precision is more than enough (10bit -> 1024 -> 360/1024= 0.35 degrees)

    • price about 15€/each
    • 10bit means in this case that there are 10pin for data + 2 power pins
  • IMU sensors for calibration :
    • BerryIMU + MPU9250 IMU chips
    • External weather shielded box which is connected directly to antenna support boom, gives you quite good compass / tilt bearings when calibrated correctly.
    • quite cheap(25€/each) and easy to use (i2c bus, RTIMULib2)
  • Slip rings:
    • https://en.wikipedia.org/wiki/Slip_ring

    • Capsule slip ring OD22MM 18Wires
    • stepper control cables and rotary sensors data cables to upper module go thru axle, with slip ring we dont have to worry about these cables and rotation.
    • about 15€
  • Stepper control:
  • Controller:
    • Raspberrypi 2 or B+
    • full OS
    • enough gpio ports for encoders and stepper control
    • network port
    • could run as "SDR streamer" with rtl_tcp or similar
    • full python
  • Connectors/box/cables/gears/belts/bolts/etc:


Plan / specs for pirotator server:

  • REST api for controlling (done)
    • you could control your rotator via simple http posts
    • enables many kind of solutions
  • Legacy rotator emulation for legacy software via virtual RS (done)
    • emulates yeasu GS-232B protocol (only control and feedback commands implemented)
    • client OS sees ?SerialPort via virtual serial port software (eg. hw-groups HW virtual serial port -HW VSP3)

    • Tested with HRD rotator and PSTrotator
  • Simpple CLI UI (70%)
    • mainly for debugging purposes
  • Multithreaded structure, and locks/aborts (90%)
    • could use all of those apis/interfaces at same time
  • Neat WEB/JavaScript UI top of REST api (15%)
    • Graphical javascipt / angular UI


This project has been pretty much in constant developement (as a hobby project), it have seen many iterations, hardware has been changed, software has been rewritten. but the main concept has been pretty much the same. And it has been on constant use since first version.

Sorry i have not been documenting all of this new stuff, if intrested i could share details via email. Sourcecode could be found here: https://bitbucket.org/wilhoj/pirotator/src

Added some pictures of current versions.




attachment:new.JPG attachment:new_az.JPG attachment:new_case.JPG attachment:new_el.JPG

attachment:imu.jpg attachment:pirotator.jpg attachment:outdoor_tests.jpg attachment:controlbox3.jpg attachment:pirotator1.jpg attachment:pirotator2.jpg attachment:slip_ring_encoder_gear.jpg attachment:controlbox.jpg attachment:controlbox2.jpg

Current commercial az/el antenna rotators are really expensive(easily over 1500€ with controllers), and moreover technically most are from 90s (analog potentiometer sensors/control, no network, rs/lpt controllable, no web, no rest api, etc).I tried to take little bit different approach..