Part Two: Here is the original picture of the finished product:


This is the second part of a 2-part series on 'How to build a High-Definition FPV UAV using a Raspberry PI with HD camera, using a high speed WiFi link.

In my first post on the subject (located here), I discussed the parts I used, and how to install them into a Hobby King Go-Discover FPV model. 

In this post, I will discuss installing the Raspberry PI and the PI camera in the Go-Discover gimbals, and the software configuration for both the Raspberry PI and the ground station PC.

From the previous post, step 3 was completed by installing the Ubiquity Rocket M5 in the model.  Now onto step 4:

Step 4: Install the Raspberry PI and PI Camera

Here is a photo of the position of the PI in the Go-Discover model:


The PI fits nicely just behind the camera gimbals, with the USB and HDMI ports on top. In the right side you can see the Cat5 network cable attached. This cable connects to the ethernet switch, which is also connected to the Rocket M5 input port.  

The two cables shown on top are the servo control wires for the gimbals, which I have directly connected to channel 4 and 5 on my radio.  I am using channel 4 (normally the rudder stick on my radio. Since there is no rudder on a flying wing, this is a convenient channel to use to move left and right with the camera. I have not (yet) moved to a head tracker, but if you already have that setup, just assign the channels accordingly.

To install the PI camera, remove the stock plate from the gimbals (for a GoPro), and mount the PI camera as shown in this photo:


The PI camera case fits very nicely into the slot, and again I used a small piece of velcro to hold it down. You could use a couple of small screws instead if you want a more secure hold.  The two gimbals servos are also shown here. They are simple to install, just follow the Go-Discover instructions.

Here is a front view of the PI camera installed:


Here is the block diagram describing all the connections:


Some comments on my previous post suggested that it is possible to eliminate the ethernet switch and serial-to-ethernet converter using the Raspberry PI and a serial port on the PI. I believe this post describes how to talk to the PI via the NavLink, but in this case, I want to use the PI to bridge the connection from the ground station to the APM/PixHawk. Somebody please comment on this if you know more about it.   I believe it would require a TCP/IP to serial link from the PI to the telemetry port on the APM, and some software on the PI to act as the bridge.  The main connection to the ground station is via the Rocket M5 and TCP/IP, not through a telemetry link (900 Mhz or Zigbee like I used on my other models).

Step 5: Getting it all to work with software configuration (the really fun part starts now).

Check out this post on what others have done with streaming and the PI.  My experiments showed that using GStreamer on both the PI and on Windows gives really good results with very low latency, if you use the right parameters. 

Get GStreamer on the PI by following this blog.   This is the same version of GStreamer that I am using on my setup. 

Make sure your PI camera works ok by plugging in the PI to a standard monitor using the HDMI port and follow the instructions on the Raspberry PI website on how to get the camera up and running (without GStreamer).  Once you have a working PI and camera, you can then proceed to stream things over the network.  

Note: It is suggested that you first get the PI streaming video by plugging it directly into your local network where you can also connect your ground station PC with the correct IP addresses (without the Rocket M5).   For my PI, I picked,  and for the ground station,    Make sure you can ping the PI from your PC and the PC from the PI.  

For streaming, you will also have to make sure all the ports you intent to use are open on the firewall (described later).

For the ground station PC,  you can download GStreamer here.  Make sure when you install, select to install everything , or full installation (not the default). 

Here is the command I use for the PI to pipe the camera output to GStreamer:

raspivid -t 0 -w 1280 -h 720 -fps 30 -b 1700000 -o - | gst-launch1.0 -v fdsrc ! h264parse config-interval=1 ! rtph264pay ! udpsink host = port= 9000

The command is explained as follows:

raspivid is the command to start the camera capture on the PI.  The -w switch is for the width in pixels, and the -h switch is for the height.  In this case, I am using 1280 X 720, but you can try any combination that fits your needs. 

The -b switch is the bit rate for the sampling. In this case I chose 1.7mbs to send over the stream. Again you can experiment with higher or lower values. This settings seems to work good for me, and the latency is almost unnoticeable.  

the "-o - |" is piping the output to gstreamer.  Make sure you include the dash before the pipe "|" symbol. 

For the GStreamer command, all the filters are separated with an exclamation point "!", as these are individual drivers that are part of GStreamer.  Since the PI has hardware accelerated video, the output is in a format called "H264", which is a highly-compressed stream. The GStreamer filters are configured to transport the output via a UDP socket connection to the target PC. Notice the 'udpsink' element which specifies the host - in this case your ground station, and the UDP port.  I am using port 9000, but you can use any open port on your system, but be sure to open the firewall or it won't work!  You can also use TCP instead of UDP, but for such a data stream, I chose to use UDP since dropouts are certainly possible, and with UDP this is ok, but with TCP, you could have socket problems and higher latency. 

Note: to get the PI to execute this command on boot, make a shell script with the above command and add it to your local.rc boot sequence. That way when the PI boots, you get the stream without having to log into the PI remotely. 

For the ground station PC, once you have installed GStreamer and opened the correct ports, use this command (from the command prompt) to view the stream:

c:\gstreamer\1.0\x86_64\bin\gst-launch-1.0 udpsrc port=9000 ! application/x-rtp,encoding-name=H264,payload=96 ! rtph264depay ! avdec_h264 ! videoconvert ! autovideosink

If all goes well, you should see the PI camera output on your PC screen in a popup window.  For those of you what want to use FPV goggles, you can connect to the HDMI port on your PC to display the output if your goggles support HDMI. 

I have this command in a batch file (with a PAUSE) statement at the end to keep the window open.

WHEW!  If you got this far, you are amazing. 

The last step to complete the build is to connect to the APM from mission planner.  The method I used to connect was to install a utility that converts a TCP connection to a virtual serial port, but I also think that directly connecting the mission planner to the TCP port will also work, however I have not tried it. I will post back later after trying it.

Here is the link to setup the serial to ethernet device to have an IP address and port.

Here is the link to the configuration utility for installing the virtual serial port.   

Once you have a serial connection over TCP/IP working to the APM, you should be able to connect with Mission Planner. On the maiden flight, it worked perfectly, and I didn't see a single drop in the telemetry data or anything noticeable in the video transmission, however my first flight was limited to 2km.

The last step is to connect the Rocket M5 to the Nano M5 and test everything using the OTA (over the air) connection. If all is well, you are ready to fly!  But be careful on your maiden, you just spent $700. 

Finally, here is a photo of my Antenna Tracker with the Nano M5 attached. My next update will include a video of a longer flight.  


Happy Flying!

E-mail me when people leave their comments –

You need to be a member of diydrones to add comments!

Join diydrones


  • Latency seems to be ok, better than with mavproxy. I have to test some more. Would be nice to get other people's opinions as well. CPU is around 40% but since ffmpeg is only like 8% I don't see a problem with the CPU load. Though it seems like some packages gets dropped now and then. I have to look in to that.

    The odroid u3 is really nice I've wanted to buy that for a long time. Just haven't got around and clicked the buy button yet.
  • @Nils : do you notice heavy cpu load (or latency ) when you use mavlink on odroid ?

    if it makes possible to go without 3eth0 switch+serial/eth0 converter, i think it is smart. Usually, more simple = less failure.

    Odroid u3 (65usd) looks attractive by the way, i guess it could do a nice GCS.

  • Just realized that I hadn't pushed the latest changes of the script to github. If anyone tried it and it didn't work its not that strange. Anyway should be working now.

  • If anybody is interested in trying out a beta version of the GStreamer-based HUD in APM Planner,  here's a link to download it:

    If you give it a try, please send me any issues like missing DLL's etc.  This is highly experimental, but it does work.

  • I have the Ubiquity WISP station in that port now. I could probably get a USB Ethernet card, which im going to buy anyway, and plug it in there. But the plan is to use that card for the Ubiquity and skip the odroid-w add on board that have the Ethernet port. The odroid-w only have one USB port so to run two USB Ethernet cards I need a hub and then I might as well use a small 3-port switch.
  • @Nils: You don't need a switch. Just use a short ethernet patch between the Rpi and the serial converter.

  • Wrote a simple python script yesterday to send mavlink data via UDP instead of TCP as ser2net uses. I really like to avoid having a switch and a serial to ethernet device mounted since my space is limited and I'd like to save as much weight as possible. 

     if anyone is interested, follow the link to download it (there is also a version that uses threads, don't use that it'll eat up all your cpu) run it with:

    python /dev/ttyAMA0 57600 <ip_to_your_gcs> 14550

    Since I have never written anything in python before there is most certainly a lot of room for improvements, suggestions are most welcome. There probably already exists something that works better than this. I tried one I found on github but couldn't make it work and then I got tired of googling and just decided to write my own. Would be nice to compare a script like this to a serial to ethernet device to see if it performs equal or which performs better. I have ordered a serial to ethernet but it will be a couple of weeks til it gets here.

    This is to get MavLink data from my Pixhawk to my GCS via a Raspberry PI - vizual54/MavLinkSerialToUDP
  • Remember that VLC has a default setting at 1000ms for a kind of buffering

  • @bocorps - no over the wifi link.  I am running 720 X 576 just to conserve a bit of bandwidth.  With VLC the delay is quite noticeable and is about 1 second however FFMPlay drops it to under 200ms - I think it is between 100 and 200ms over my 2.4Ghz MikroTik link.  Mind you I have managed to sell most of my gear now as one large house owner wanted wifi all over his property so no he has it almost down to the local shops.

    If I use H.264 with Derek Malloy's implementation then the latency increases however the bandwidth is less than half at 3M for 1920X1080.  MPEG 1920X1080 uses about 25M however is quite low latency.

  • @stephen : you get 100ms when C920 is directly plugged on PC or when everything is installed ?

    @ Patrick : What is the advantage to use gstreamer and not directly ffmpeg in this project since i see gstreamer as another layer ? 

This reply was deleted.