Rotator done - eliminated Arduino

I started the project in February 2019

I had trouble with suppliers from China, and then I had a knee replacement surgery, so it took 6 months to complete. Here are two pictures of the completed rotator:

I completely eliminated the Arduino. I connected a motor hat to the Pi c/w matching stepper motors, and wrote a program for the Pi to emulate an Easycomm rotator. The rotator works fine with GPredict - I haven’t tested yet with the Satnogs Pi program.

The antenna is a 3 element yagi tuned for 137.1 MHz; so far mediocre response due to obstructed passes.


Is that a deer in the background?

Is the way the yagi is mounted affecting it’s pattern? Seems like the rotator/tripod would act as a parasitic element due to the yagi being so close.


Look close and you will see two deer fawns. The doe was hanging around, but didn’t care about the rotator.

I didn’t think that metal behind the reflector element would impact a yagi, but I’m open to suggestions.

I can only see the one, but my eyesight kept me out the cockpit, so not surprising.

Only one way to find out if it affects it or not. I used to use a tripod mounted Arrow II crossed yagi for portable sat work, and would notice some funky stuff when the 2m antenna was twisted to be vertical, and somewhat lined up with the tripod mast. It wasn’t a lot, but noticeable. You may not experience any issues at all.

Heye eejake52

This is great. It couldn’t be easier.
The control system consists of easily available boards, just plug and play without having to solder much.

Some questions of course …

  • in the photo I see 2 power supplies, both run to the steppe motor hat, one for the steppe motor power supply, the other for? (green cable to extra connection on motor hat)
  • you are talking about controlling the rotator via the RPI. Do you also run gpredict on the RPI or do you send the data via lan to the RPI and does gpredict run on an external PC?

Are electrical diagrams available?

You have also written a program for the RPI to work with the easycomm protocol.
Will this become available to the community, or is it possible to get a copy of it?

This seems to be a nice alternative to the existing rotator controls, something that I have an interest in replicating.


The small power supplies are adjustable. One is set to 12Vdc for the stepper motors, the other is set to 5Vdc to power the Raspberry Pi.

The Pi is running headless, so I am using xrdp to control the Pi UI from inside the garage.
On the Pi, I run:
All this shows a CPU load of about 50% on the Pi 3B.

I didn’t make any electrical diagrams. There is a fuse on the 24Vdc input, two DC/DC converters, and the wires to the stepper motors per their datasheets. I didn’t install the endstop limit switches on the rotator shafts.

I’m willing to share the program, but I’m still working some issues. For example, GPredict only updates the desired positions once per second - as a result the motion is somewhat jerky for small changes.

If you decide to replicate this approach, keep in touch on this list and I’ll provide more info.


Hello Jake

The parts are ordered, motor hat v2 and 2 stepper motors 12v 1.2a
I still have RPI 3b.

To understand your remark about the jerky motion i found a graph with the angular velocity of the azu rotor with respect to time.
Hereby you see that with a transition of say 82 ° elev the azu motor must run 180 ° in a very short time if the elev is max 90 ° (no flipover).
This means about 4 ° / sec, while in normal circumstances a 0.5 ° / sec is sufficient to follow a sat.

When I think of a fixed motor speed, I think I understand your problem (jerky movement) with small angle adjustments.
Something to test could be to adjust the motor speed to the size of the angle adjustment.

No matter how well you steer, your antenna always comes to the point where the sat was, but as long as the sat falls into the main lobe of the antenna, it doesn’t matter.
So btw if speed is a little bit to slow, you get a very smooth movement. it is now to find out how slow you can go…

Well my 50 cent idee, i hope it helps.

Please keep me updated with the tests …


Here is the software I wrote:

The instructions assume you already know how to run a Python program.

Let me know if it works (or not) for you.


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Hello Jake

THX for all the help already.
I am still waiting for some parts coming from china.
When everything is assembled and testing starts, I will let you know how things are going.