SARCNET Mini Satellite-Antenna Rotator Mk2

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SARCNET Mini Satellite-Antenna Rotator Mk2

Published by Julie & Joe in Satellites · Saturday 24 Aug 2019
This forum is all about our medium-duty, mini satellite-antenna rotator Mk2, which is capable of rotating two, 3m long, cross-polarised Yagis.

We want to hear from readers and sort out problems with procuring the required roller-chain sprockets and other problems with the long-haul serial link.

Julie and Joe
Sunday 09 Aug 2020
Hi Scandio,

A 5m length of the USB cable should not be a problem. Our Mini Satellite-Antenna rotator is a finely-tuned, closed-loop feedback control system. There are many reasons why readers have reported that it did not behave as expected:

1.Incorrect wiring (particularly motor wiring reversal or grounding)
2.Incorrect software configuration or loading
3.Component substitution
4.Not attaching the sensor to the lift arm
5.Non-rigid attachment of the antenna and tripod
6.Incorrect 3D Sensor calibration
7.Incorrect external controller configuration

Please check these first so we can help you. Note that most readers and our own testing report completely satisfactory operation.

The addition of limit switches is possible, but problematic in terms of design and application. An azimuth, anti-windup lanyard and pull-off micro-switch was considered. An elevation tilt switch (not mercury type) was considered. However, in keeping with the design goals for the project they were rejected due to cost and complexity, the conducted safety testing and the stated precautions. As a DIY project, such additions are the builder’s prerogative.

When building a DIY project, we reiterate that safety is the most important consideration.

The instructions state: “Connect Motor Driver 12V and GND terminals to your 12V supply via a cutoff switch and fuse (Caution: Don't connect until safe: The motors may move)”

All the bench testing at https://www.sarc...
Scandio i2WQ
Saturday 08 Aug 2020
the mini rotor was completed and I started the tests;
the USB connection was made with a 5 meter cable;
however there was a problem: rotation after a command
it did not stop and the 12 V power cable was damaged;
I suppose such a long USB connection is not reliable:
however wouldn't it be safer to introduce a hardware lock?
(e.g. limit switch reed contact)
do you have any news of problems of this type?
now I'm on vacation: on my return I will try an RS422 connection

Julie and Joe
Sunday 19 Jul 2020
Hi Scandio,
The correct sensor orientation is shown here:
It is most likely that you have the elevation motor wiring reversed. Please use this test to confirm the correct operation:
a. Hold the 3D Sensor in your hand with the flat side down and the front side (opposite the cable) pointing North.
b. Point the 3D Sensor upward: The EL Motor hub should turn counter-clockwise.
c. Point the 3D Sensor downward: The EL Motor hub should turn clockwise.
d. Point the 3D Sensor to the East: The AZ Motor hub should turn counter-clockwise.
e. Point the 3D Sensor to the West: The AZ Motor hub should turn clockwise.
The 0.6 RPM motors are readily available on eBay. Anything faster will be quite unstable and have insufficient torque.
Good luck!
Kind regards
Julie and Joe.
Scandio i2WQ
Sunday 19 Jul 2020
something wrong with my calibration procedure?
I followed your the video

calculation for my site:
lat. = 45° 35’ 41” N
long.= 8° 54' 23" E
decl. = 2° 54’ E > (54/60 +2) = (0,90 +2) > 2.9

sensor: LSM303DLHC
I have to place sensor with i.c. upwards, X axis towards boom antenna

in these conditions:
at rest true north pointing ok
command 00 45 rotates downwards and not upwards
I tried to change the sensor orientation but no solution

to avoid interpretation errors in your video it would be better
to use a sensor without cover, fixing with transparent tape
or indicate on the sensor direction Y, X and i.c. if at the top

what did i do wrong ??

another question:

0.6 RPM engines are difficult to find
while the 5 or 6 RPM ones are more common

a sw solution is possible to obtain a slower rotation ??

Julie & Joe
Saturday 11 Jul 2020
Hi Scandio,
That’s great news. Please mention in your article that our primary mission is to engage primary school students in science and technology, engineering and mathematics using the resources of Amateur Radio. We would encourage all Amateur Radio clubs to do the same.

Kind regards and stay safe.
73, Julie and Joe
Scandui i2WQ
Saturday 11 Jul 2020
thanks for the quick response:
found the problem: the CR set was missing;

can I translate part of your article for the Italian Hams magazine " Radio Rivista" ??

Julie and Joe
Saturday 11 Jul 2020
Hi Scandio,
First make sure you have the correct configuration for the sensor and serial port:
//User configuration section:
//Please uncomment only one of each of the following MotorTypes, SensorTypes and SerialPort types:
//const int MotorType = PWMDIR; //Please uncomment this line for the LMD18200T DC motor driver.
//const int MotorType = FWDREV; //Please uncomment this line for the L298N DC motor driver.
const int MotorType = ACMOTR; //Please uncomment this line for the triac AC motor driver.
//const int SensorType = LSM303D; //Please uncomment this line to use the LSM303D sensor.
const int SensorType = LSM303DLHC; //Please uncomment this line to use the LSM303DLHC sensor.
#define SerialPort Serial //Please uncomment this line to use the USB port.
//#define SerialPort Serial1 //Please uncomment this line to use the TTL port.

Then check that the Serial Monitor settings: 9600baud and terminated with a Carriage Return.

Are any of the other commands working, or is it only the b command? e.g. The 'r' should return the calibration settings.

Let us know how you get on.

Kind regards and stay safe,
Julie and Joe.
Scandio i2WQ
Saturday 11 Jul 2020
thanks for Rotator6 sw; but testing i found a problem: with "b" command on the serial monitor nothing appears;
I tried a test sw from POLOLU firm for LSM303DLHC (with its library) and with this the data are displayed; so connections and sensor are ok ; (the connection is about 40 cm long): any suggestion ?

Jharwin DV2JB
Monday 18 May 2020
Sorry Francesco, I wasn't notified by your question. As of January 2020, I was able to modify the rotator6 code (almost rewrote it) to make it compatible with esp8266 environment library. My rotator now runs completely off any Arduino board and just the bare wemos D1 lite. No need for any USB cable. And wemos d1 is so cheap that you can get for only $3 a piece.

To tell you a little about what I did in terms of implementation, currently the rotator6 talks to the computer via serial port. It's the main reason why we're limited to only a couple of meters of USB cable to be able to talk to the Arduino. But using esp8266 wifi capability, I was able to rewrite the code, run the code within in, that instead of throwing data via serial port, it's now throwing data to a telnet client. (wirelessly) The esp8266 acts like a telnet server and another computer connected to the same wifi which esp8266 is connected to can talk via telnet.

I can still do the rest of the command, like calibrating, monitoring, demo etc as well as the auto parsing of data if the incoming data is an easycomm2 protocol format or just manual control by entering digits (ie. 120 90)
Julie & Joe
Monday 13 Apr 2020
Hi Trent,
There is some information about larger H-Bridges at Search eBay for a BTS7960B dual 43A driver. The software handles both FWD/REV and PWM/DIR driver types. The Mini Satellite-Antenna Rotator MK2 is already a version using chains or timing belts. See: This will handle two large counterbalanced Yagis. Or did you want something larger?
Kind regards, stay safe,
Julie and Joe.
Monday 13 Apr 2020
Hi,Im going to make 2 of these kits but as I want to upgrade it does anyone know of any bigger PWM H-bridges that its compatible with and that are cheap?
also has anyone thought about doing a upgrade kit for the mechanical side of it like timing sprockets,chains and bearings cause I find it hard to find anything here in tassie,,let alone getting someone to make up a base plate for the upgrade
Francesco IW0DJC
Sunday 02 Feb 2020
Hi Jharwin/DV2JB. Did you get it working straight or you got to modify rotor6 code ?
73 de Francesco
Jharwin DV2JB
Thursday 09 Jan 2020
Hi everyone, just a little update on my mk2 rotator project. I was able to use a NodeMCU esp8266 running ESP-LINK to the Arduino micro of the rotator. This makes the rotator totally wireless from the box to the shack! Next step for me is to finalize where to exactly put the mast, because I'm planning to install this totally outdoor. Currently, the rotator and the antenna are just sitting on a tripod at the backyard, doing a lot of hard testing and checking what might break (better to service and troubleshoot it while it's still in the ground than climbing a mast to put it down for repair). I also made some changes to the Arduino sketch wind-up logic to avoid the coax being tangled but that is entirely for my application!
73, jharwin

Monday 30 Sep 2019
Hi....I have been quit brutal changing parameters and changing satellites while still tracking and everything is rock solid and performing perfectly. Frankly I am astounded. It is a thing of beauty to watch as it tracks whatever I tell it to or track manually using GPredict Rotator Control." Here is David's Mk1a version with the LSM303DLHC sensor and L298N motor driver board
Julie & Joe
Wednesday 25 Sep 2019
Hi Jharwin,
You are fortunate to have found the sprockets. There is now a pulley and timing belt version on the website. We don't think machining the tube is a realistic option. You would have to turn down at least half the horizontal tube and the top of the vertical one. You might find it easier to bore out the sprockets and bearings. Anyway good luck with your project.
Kind regards,
Julie and Joe.
Jharwin DV2JB
Monday 23 Sep 2019
Hi all,

First, Julie and Joe, great job and amazing work sharing this project to everyone.

Btw, a friend of mine from Taiwan who I've just met via satellite qso and later on followed each other on twitter. Co-incidentally after me tweeting the mk2 project as my next project (i actually built the lightweight version of the rotator, but I need something more sturdy :)) I didn't know he was also building one, so he sent me a dm and found out that he got everything almost 90% complete even the sprockets which he has sourced from Taiwan. I have mentioned I've been struggling to find the sprockets and good amateur camaraderie of him, sent me those sprockets because he said can get it anytime he wants. He even asked me if there are any parts that I am still struggling to find and I told him the company that sells the enclosure hasn't yet replied to me if they can ship the item in the Philippines. SO, he also sent me the original FT202015 enclosure. So nice to have a ham friend overseas!!

Now here's my new latest problem, I can't find a good machine shop here in the Philippines that can lathe my 25.4mm aluminum tubing into a 25mm :(

It looks like most aluminum suppliers I talked to only carry 1 inch OD tubings or should I say, equivalent to 25mm OD, and here they don't seem to acknowledge metric-sized at all.

Hoping I could find one soon locally, crossing my fingers on this!

Julie & Joe
Thursday 29 Aug 2019
Hi Everyone,
For over a year now we have been lamenting the difficulty in obtaining the sprockets and roller-chain required for our Mini Satellite-Antenna Rotator Mk2, as all the on-line sources have dried up. Then, Mark, Technical Director of, surprised us both by finding a cheap source of substitute pulleys and timing belts on eBay. They look like they should do the job and we can't wait to give them a try. If you are interested, have a look at Thanks again Mark for your help.
Kind regards,
Julie and Joe
Robert VK6FRDM
Saturday 24 Aug 2019
Home button: Just enter 0/0.
Working well with Denis VK6AKR. We now have two working. Now working on the larger one.
A thought we have is the I2C run: Instead of that to have let’s say the mini is in the shack and another is out side, the one out side has only the motors in it.
Which means only the power cables to rotator, the mini in the shack becomes the rotator controller, in a sense, the one in shack controls both rotators, the one in shack is controlling 4 motors.
If possible it would eliminate cable length for I2C and USB. Just a thought.
Julie & Joe
Saturday 24 Aug 2019
Hi Robert,
Thanks for the website information we will check it out. Good job on getting the rotator built.

Regarding the home button, you can pretty much point the antenna anywhere you want using Gpredict. Have a try with that and then let us know if you still need the button.

Kind regards and keep in touch,
Julie and Joe.
Robert VK6FRDM
Saturday 24 Aug 2019
Hi Julie
Many thanks to Denis VK6AKR with helping get our first rotator working very much a joint effort
He has asked me to inform about the sprockets
Here is the web site:
I have asked them to look into spur gears as well
An other site to look at is:
I wonder if possible to have a home button to reset rotator to start position after sat is out of range? My first effort on the forum
Denis VK6AKR
Saturday 24 Aug 2019
Hello all,
In regards sourcing the sprockets I will get Robert to comment - hopefully also to join the forum. We both did our fair share of Googling but he got a result ahead of me. Need to have them bored out, a project for slightly later.

Happy to be a tester for other long-line comms ideas. In my professional life (read "younger days" hi hi) RS422 was a good fit in the medical data environment and there were a number of National Semi, Texas Instruments and Fairchild chips that were robust. Forget their details though from this distance in time. I would probably fight shy of WiFi due to the cluttering of spectrum but maybe that's just me! Battery + solar panel notwithstanding, probably need some form of power wiring anyway so adding a few more wires for control purposes should not be too much of a burden.
73, Denis
Julie & Joe
Saturday 24 Aug 2019
Hi Denis,
Please let us know about the hassles you have had sourcing the sprockets from the US. We would like to let everyone know what is going on with the company and how to circumvent the problems. We have actually been thinking about another approach to sprockets.

Did we mention we are looking at both WiFi and LORA solutions to replace the RS-422 long-haul link as some readers have had problems blowing up the RS-485 drivers with voltage spikes. We have both new designs working over a reasonable distance and will publish the designs shortly. Would you like to be beta testers (er, guinea pigs)?
73, Julie and Joe
Denis VK6AKR
Saturday 24 Aug 2019
Hello all,
The Mk2's sprockets and chains caused us some interesting hassles sourcing, but we will be getting there by boring out the bosses of some Australian-sourced parts to suit our 25mm tubing.
73, Denis VK6AKR
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