How to build an FPV Antenna tracker for use with Mission Planner

For anybody interested in improving the range of your FPV and the quality of the signal (and still stay FCC legal), and antenna tracking could be for you. After looking around for a 'stock' solution I decided to build one myself. Above is a photo of the final product.

I am using the 5.8Ghz band for my FPV configuration, and this keeps the antenna small and the entire package very compact and portable. There are two stock full-size servos and a servo base that I purchased from ServoCity.com.

I will not say that this solution is 'cheap', but it is very effective. I have yet to fly my plane out of range where I lose the  video so I cannot say what the exact range is, but I have not gone beyond 2 miles using a 500mw transmitter. The receiver antenna is a spiral RHCP (Right-hand-circularly polarized) antenna which has 16 turns! With this configuration the gain is 16dbi, which is excellent, but it's also very directional, and hence the need for the tracker. 

The total cost of this rig was about $280 (plus the work to assemble it).   Half the cost is the servo and the servo mounts and gears. The other half is the antenna and the Arduino. 

The link to the antenna is here (ReadyMadyRC). There are a number of other antennas that will work with this tracker as long as the footprint is not too big, but for 5.8ghz this is usually not an issue. To attach this antenna to the servo, I simply used a strip of Velcro so it can be easily removed. It is light enough that the Velcro holds it perfectly.

Here is the parts list for the servos: (ServoCity.com)

Qty  Description                             Unit                Amount
--------------------------------------------------------------------------------
1     (DDT500F) Direct Drive Tilt (Futaba)   $24.99              $24.99
       * Weight: 0.22 lbs. each

1     (SPG5485A-BM-36005U) Bottom Mount      $99.99              $99.99
         Servo Power Gearbox - 360 Degree
         Rotation
       * Weight: 0.62 lbs. each
       * Option: Servo is HS-5485HB          $24.99              $24.99
       * Option: Ratio is 5:1 Metal Gears
       * Option: Kit is Unassembled

1     (FUTM0718) (03.06.02) S3072HV Servo    $39.99              $39.99
       * Weight: 0.18 lbs. each

4     (91772A146) 6-32x3/8 inch  Pan Head    $0.17               $0.68
         Phillips Machine Screws (Stainless
         Steel)
       * Weight: 0.01 lbs. each

--------------------------------------------------------------------------------
     Total Shipment Weight: 1.23 lbs.   Subtotal:                $190.64
                                        Shipping & Handling:     $6.99
                                        Total:                   $197.63

You can choose different servos if you prefer to spend the money (or go on the cheap), if you can find them elsewhere, they are just standard size servos.  

You can also buy the kit with the servo included and pre-assembled, (additional $30 cost). Here is a link to the servo kit

If you are not good with a soldering iron, pay the extra. You will need to disassemble one of your servos, disconnect the potentiometer  wires, and re-solder them to the external one supplied in the gear box. The external feedback will allow your tracker to move 360 degrees in the azmuth. 

Also, I chose the 5:1 gear ratio, and this seems to work very well, even at full speed, there is no jerking and the tracker tracks the plane perfectly. A lower ration could make it jerky, but it may also work. 

Assembling the servo box is not too difficult but will take you about an hour (plus wiring if you buy the bare kit). I would suggest paying extra for the pre-assemble servo base as I found modifying the servo to be an 'advanced' activity, however I was able to pull it off without losing parts or damaging the servo.  All the instructions come with the kit, so I will not go into detail here on how to assemble the pan/tilt box.

The assembled serve pan/tilt will should look like this:

Part 2: The Arduino and Misson Planner communications to control the servos

Now comes the fun part. Controlling the servos. I am using a standard Arduino Uno board which you can purchase just about anywhere. Here is a sample link, Arduino Uno that cost $25. 

I also added the 'Servo Shield' to my Arduino, however I think it's possible to just wire the pins directly to the Uno without the shield, but the shield has the standard servo pins.  Here is the link to the servo shield.

To connect the servos to the Arduino, just use the standard connectors that come with the servo. No wiring necessary if you use the Servo Shield. You can pick any servo port on the Arduino, just take care to make sure the software is using the pins that you have selected to control the servos.

The ground wire on the servo (usually black or brown) should go toward the "G"  and the signal side (usually yellow) goes to the "S" label on the Servo Shield. If you do not use the shield, you will have to solder the wires or install your own plug on the Arduino.

For the servo power, I have chosen to use the power supplied by the Arduino through the USB port and for two standard size servos, this seems to work fine with a lightweight antenna. If the load becomes too big, you could trigger the on-board fuse, so in that case you may consider using an external power supply for the servos. So far, I have not had an issue with just using the power from the Arduino and the computer's USB port which will supply 500mA. 

Here is an image of the shield (use the digital servo ports shown labeled GVS):

Connected to the Arduino (and enclosed in a metal case), the assembled unit looks like this:

Part 3: Make it work with Mission Planner:

So after all this 'hardware' assembly, you will want to test it out to see if it works with mission planner. BUT you will need some software to run on the Arduino.  Here is the source code that I used:

ArduTracker.ino

Everything is done over the Arduino serial port when Mission Planner connects to the Arduino. I picked to hard-code a serial port baud rate of 57600.

There are two lines of code that determine which pins on your board will control the servos:

pan.attach(9);
tilt.attach(10);

On my board, I used pins 9 and 10 which end up being the first two servo ports on the Servo shield. 

There is one line of code that controls the pan calibration that I figured out using trial and error and some calculations to make the pan go 360 using the 5:1 gear ratio:

   interpVal = ((interpVal * 10) / 37) + 50;

   pan.write(interpVal);

   

   The inputs (interpVal) are PPM values sent by Mission Planner. The hard part is done in Mission Planner as it computes the PPM servo values from the GPS coordinates. To make it work with this setup, you will need to 'tweek' the values for your servos and the gear ratio of the pan gear box. If you duplicate the setup I have described, you should be able to load the firmware into the Arduino and simply connect the Mission Planner and it should work (in theory!). 

Load the Mission Planner and go to the "Initial Setup" tab, and select "Antenna Tracker" as shown below:

Using the default values shown here, (and your serial port), you should be able to connect and control the servos using the 'Trim' sliders. If everything is working ok, you should see the servos move to their extreme positions (pan = 360 deg), and (tilt = 90). The tilt will go from horizontal to the ground, to vertical straight up. 

If all is well, then you can try it in the field. Just plug it in, and connect, and Mission Planner does the rest.

Happy flying!

Views: 46965

Comment by Don Rann on October 19, 2014 at 11:30pm

Patrick, I forgot to mention. My tracker seemed to get confused when the Tracker Home was too close to the plane.  I overcame this by setting Tracker Home 10 metres behind the pit location.  Regards.

Comment by Patrick Duffy on October 20, 2014 at 4:28am

@Don,  That happens because of the resolution of the GPS is only a few meters. I just ignore the twitching, but your solution sounds better.

Comment by Patrick Duffy on October 20, 2014 at 6:20am

@Don, Great work on that tracker. Can you post your arduino code in case someone else is interested?  I have since upgraded mine to be a full HD digital system with using two helical 5.8GHz RHCP/LHCP antennas and a Ubiquity Rocket M5. I can now do full HD FPV using this tracker platform. Someone could make a business out of this if they wanted to make the investment. 

Comment by Julien on December 16, 2014 at 1:11pm
Hi Patrick,
Thank you for the job!
I m new to arduino and i just want to be sure of what you mean by the serial port of the uno board. Can i set it up by the usb port or do i have to connect it via an ftdi or usbasp adapter?
thank you,
Julien
Comment by Patrick Duffy on December 16, 2014 at 1:30pm

@Julien,  the USB port is an FTDI device on the arduino.   If you are running on Windows, it should recognize it as a serial device and add it to the list in device manager.

Comment by Julien on December 17, 2014 at 5:17am

@Patrick,

My problem was that i have a DccEle - DCcduino Mega 2560, a clone of arduino uno, and the drivers are differents. I finally found them on a russian website, and it works perfectly after little adjustments. Thanks for all!!!

Comment by Jeff Smith on February 9, 2015 at 9:33am

@Patrick, I too have purchased a clone board. The difference with mine is that it uses a CH340T instead of Atmega16U2. I cannot get the board to communicate with MP, even at the reduced 57k. Have you used this chipset before? It is stated to be functionally the same as the U2. Any suggestions beyond returning it for credit?

Comment by Patrick Duffy on February 9, 2015 at 10:22am

@Jeff,  Can you get the serial port to communicate with a test script?  Since it's just a FTDI interface, the PC does not know the difference if there is a different chipset, unless for some reason the script itself won't run, it should make no difference to MP.   I would write a very simple test script that just reads bytes from the serial port and echos them back. Then you can a terminal, such as 'Putty' to connect and check if the port is ok.  

Comment by Jeff Smith on February 9, 2015 at 2:49pm

@Patrick, It appears the sellers were trying to pull one over on some unsuspecting people. In checking into this further I have found that the processor isn't as promised either. Instead of a Mega528P, it is a Mega 8B. I have requested a refund, and will get a "real" unit shortly. Thanks for your help... 

Comment by Keith G on February 22, 2015 at 12:18am
Just curious, has anybody tried using an APM or pixhawk to control the tracker. I've been trying to use the firmware and a spare apm but have had no luck myself. I'm about to toss in the towel and go with your method. Lol.

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