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 192.168.1.2, and for the ground station, 192.168.1.1. 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 = 192.168.1.1 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!
Comments
@Patrick, Been learning a lot from your blog. I'm a Noob and have to rely on great work of others to make sense of this technology. Re - Raspberry Pi drivers for 8812au; I found this link to work by MrEngman
"The full post on how to install the Realtek RTL8812AU driver module is available on the raspberrypi.org... ".
Might be of use to someone? It solved my problem with installing Edimax EW-7811UAC on RPi2
@Patrick,Sorry for delete this post. for using the other user the second schematic in this below :
@babak_ea Your second example in the schematic is the setup I am using. The 'access point' is the Ubiquity NanoBeam, and the USB WiFi Dongle is a Netis WF2561. You can see it in the pictures in the post from Sept 20th.
@babak_ea, The way I am using the adapter is to connect from the PI to the NanoBeam, when the NanoBeam is the access point. If you have an adapter that is supported in the PI kernel, then no need to build the driver. The driver I am using is the 8812au linux, which is not currently supported. You can download from the web, or if you have a disk from the manufacturer of your adapter, it may be on the CD. To build on the PI, you need to get the kernel headers for the version of the kernel you have on your PI. If you run "sudo rpi-source" that should work to get the source. You may have to install the 'rpi-source' utility first. Follow the directions in this link:
https://github.com/notro/rpi-source/wiki
@Patrick, Thanks for your Support.
I would like use USB WIFI Dongle but need more explain and guide about how I Can use software AP mode on raspberry pi and compile it. I prefer that use alfa awus036nhr v2 because It's cheap and it has high power RF output, also support software AP mode.( My radio control frequency band is 433 mhz)
@Sam, it's the same tracker, but without the 'tilt' servo. I eliminated the tilt using the dish because of the beamwidth vs. the altitude that the UAV flys is within the 10 degrees of range of the spec of the Nanobeam. You really don't need to tilt the antenna because as you fly farther away from the base, the angle settles to about 5 to 7 degrees above the horizon. So unless you are flying at many thousands of feet above the ground fairly near the home position, you really don't need the tilt. This is especially true with mult-rotors, as the usual altitude limit is < 400 ft.
Awesome thanks. Your tutorials are really well written. Is that the antenna tracker on the nanobeam that you built in the other post?
@Sam, if you want to use the M5, it's flexible as to which antenna you pick, unlike the Nano or Nanobeam, which have integrated antennas. You can use a dish, or the helical setup for MIMO. For MIMO you would need a dish with two elements, one horizontal and one vertical. Each channel would have a single cable going to the two elements in the dish, no need for any splitter or other hardware. Ubiquity sells the dish/M5 combo but it's more expensive than the NanoBeam. A MIMO configuration will give you a more robust connection since you have two independent channels, but it's not absolutely necessary to have it. You can use a high-power wifi adapter to get virtually the same range as the M5 and use one channel.
Here's a picture of the NanoBeam setup I am using:
And a WiFi dongle attached to a quadcopter: The dongle is a Netis 500mW dual-band USB, and the antennas are two clovers, but dipoles also work just fine.
@Patrick_Duffy Thankyou. Its very interesting using the NanoBeam I would have never thought of that. Would it be possible to create a diversity setup on the M5. Like using a wide directional antenna maybe a patch and then using a parabolic dish(For super long range). Could you do this just by splitting the SMA cable or would you need a special module to split the module.
Im not really set on doing this but it sounds like an interesting concept.
@Sam, Yes, that will work. I have a setup that has two 14dbi helical (LH/RH) antennas mounted to a M5, and the clover leafs on the UAV. I get pretty good performance with it, but I have found that the noise floor with the Rocket M5 is not as good as the integrated antennas, so I am using another setup for long range. For <10km, the dual helical setup will work. I have another setup that uses a linearly-polarized dish (Ubiquity NanoBeam), on the ground, attached to a tracker. The dish has 24dbi gain, but you need an accurate tracker and good calibration to make it work. With the dish, I can get 15 to 20km range. I haven't actually found the limit to the range, but the signal is around -94dbm at 20km, which is on the hairy edge of it's noise floor. If you have a tracker, you might consider the dish if you want better range. For the dish, you can use either the clovers, or a dipole. The clovers will give you better multi-path rejection, but you lose 3db because of the polarization to the linear-polarized dish, but the lower noise makes it about the same as a dipole. I have found that there is virtually no difference between using the dipole vs. the clover with the dish, but with the helicals, the clovers are better.
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