Iron sample for HD FPV *

* Oh, I feel, holivory will now begin

Virtual Virtualka's first flight as a broadcast HD camera

Introduction

About FPV has already written a lot on Habré, but in order to minimize the amount of boiling up in the comments, let's agree at once:
')

• FPV - First Person View, first-person view. This can be either the control of a flying / driving / floating / forward-looking device with simultaneous observation through the camera installed on it, or independent control and monitoring.
• In the case of flights - they are "far and high" and "low and close." Of course, there are many variations, but these are the main parameters.
  
• Flights are fast (airplanes) and slow (multikopter). Again, and the plane can soar slowly, and the fighter roast in full, there are many options.
  

So, everything written below applies, first of all, for slow, "low and close" options. But I hope that in the near future it will be possible both far and high.

Prehistory

When I first put on my FatShark glasses, which showed a picture from an analog video transmitter, I was amazed how bad it was. Viewing angles, resolution, price. Analog video signal - interference, interference and interference again. A lot of tricks to minimize this very interference, as well as to prevent interference on the control channel. Of course, many do not like this state of affairs and want improvements. I would like a digital communication channel, digital video, preferably one common communication channel for video and control, glasses / helmet with HD resolution ...

In many modeling forums, this topic is periodically raised, but usually it meets fierce hatred from experienced modellers who are used to good old proven systems. It is difficult to argue with them, as there is a reason for their criticism. But nobody wants to want the best.

By the way, I recommend - an extensive discussion of the topic on rcdesign.ru

My first attempt to get a high video resolution using analog transmitters was described in this topic . The scheme turned out with a minimum signal delay, but cumbersome and voracious, so it did not go further than home tests.

The second attempt was made literally the other day, which will be discussed in this topic.

Test equipment

Probably, many have already heard about our microcontroller called Virtualulka . She thought only for working with video of normal resolution, optimal for smart control over the Internet. But when we finally got HD video on it (1280x720 pixels resolution), we immediately got a crazy idea - why not try using it as a course (or, at least, overview) camera in the field of local use without any Internet . I wanted to put it on a plane or a kopter and see what came of it.

The native Wi-Fi module is not suitable for this application - it is exclusively for home use, and for an acceptable range, you need something more powerful and more serious with an antenna. So the only way out is a separate transceiver connected to some interface. Since we only consider Wi-Fi as a communication channel, it turns out that we need a compact and lightweight Wi-Fi router that can be connected to the Ethernet connector.

With Virtual at Virtualka, at the moment things are like this: the native controller is inactive, instead of it, the ks8851 chip, which sits on the SPI bus, is added to the board. This was done in order to use interruptions on the pins when using Virturilki for its intended purpose (the onboard brain and the video coder of any moving pieces). Native Ethernet, although it uses only one interrupt, makes the others inaccessible. For this reason alone, we had to do without it, but, just in case, we left the possibility of connecting it on the “second floor”. And the ks8851 chip turned out to be too leisurely, obviously not suitable for video transmission.

In short, our apparatchik Sasha urgently makes the second floor for the native ethernet, while we are getting out of the means at hand - we use the usual purchased USB-Ethernet adapters. It turns out quite cumbersome, but to test the technology will fit.

It turned out this

connection diagram

"Board" part

• Our ordinary HD camera is connected to Virturilka;
• We insert the USB-OTG adapter into the Virturilka, we plug the USB-Ethernet adapter into it;
• We connect the popular Ubiquity Picostation router to the USB-Ethernet adapter;
• The Picostation is powered by an onboard battery (PoE power supply, in blue and brown pairs), and the Virturilla is powered by it;
• Ubiquity Picostation is configured to connect to the "ground part" - a Ubiquity Nanobridge dish.

"Ground" part

• Ubiquity Nanobridge is connected with a normal twisted pair to a laptop (power is also PoE, or from a battery, or from a PoE power supply);
• Video glasses are connected to the laptop.

We have two test kits for routers, 2.4 and 5.8 GHz. But for now we are trying only a kit which is at 5.8 GHz, since it is relevant at the exhibition, about which a bit later.

Monstranovenko, but as soon as the motherboard with the native ethernet is ready for Virturilki, everything will be greatly simplified on the onboard side at once.

It is worth a little distracted by the situation with glasses. Understandably, fatsharks are no longer suitable, as they can only display an analog video signal. The first option was - Headplay glasses, which are also quite common among photo players, since they can display both analog video and digital (there is a VGA connector for connecting to a computer). But Headplay has another problem - the resolution is only 800x600. And somehow it is stupid to take on board video at a resolution of 1280x720, and look at small screens with a lower resolution.

The search for other options did not help much, either experimental models that are not on sale, or expensive monsters like the Sony HMZ-T3 . We have almost agreed to Sony (there you can also arrange “3D”, in general, it's super), but familiar modellers suggested the coordinates of the person who is developing such glasses himself. Neither I nor my colleagues had ever even heard about homemade glasses, so I was very interested.

The glasses turned out to be like this . Externally, they look great, the resolution is 1280x720, the viewing angle is declared about 90 degrees. They can display an analog signal (RCA connector, aka "tulip") and digital - via the HDMI connector. In general, a fairy tale, judging by the description. Looking ahead, I will say that I tried them in, did not disappoint.

These are the glasses, but the author is constantly refining them, the new model is different in appearance from the one in the photo.


I also note that in St. Petersburg at the same time other points were tested, more like a helmet:

Here is their discussion and the author's site.
We can say that these are two different "schools" of the production of glasses / helmets - the difference in optics and other details. I am glad that both models are made by our guys.

Home trials

As usual, the above scheme was tested at home. Copy - paste on Habré is not welcome, so I’ll just give you a link, if anyone is interested - www.g0l.ru/blog/n3926

Garage Tests

Since everything worked at home in an excellent way, it was decided to conduct tests on something really flying. Because it wasn’t summer weather, I didn’t really want to go to the field with the plane, and it was too early to test it on the plane, so we began to look for familiar kopterists. Thanks to the guys from “Garage №17” for supporting and inviting them to conduct tests on their territory, on their copter.

Thus, the first flight of Virtuurka as a course HD camcorder took place on a heksakoptere with the controller NAZA.





There was a decent wind, but NAZA was doing great. Virtuirlka also did not let us down. Far from flying away, because it was still scary, the first test and all that. Unfortunately, the thought came late that the video stream had to be recorded in the form in which it was received on a laptop. So from those tests there is only a video shot on GoPro. Video from the screen from the screen recorded, horror, of course, but at least something.

The delay did not work out at that time, again, for a stupid reason - the guys in the garage had Headplay glasses, but there was no VGA cable. And I forgot to take this same cable. And it’s unrealistic to control the picture on the laptop screen - it lights up everything on the street, there is little space between the garages, it's scary. In general, there were a lot of jambs, but there was a lot of joy too - Virtuirlka flew, transmitting video from board to ground, not a single drop (packet loss, frame spilling). The delay was appreciated by eye - no worse than at home, i.e. somewhere 180-250 ms. At least the use as a review camera is already real. With a quiet control of the copter (fly, look in glasses HD picture from the board) - normal. For nimble aerobatics, of course, a bit too much.

The first link test for HD FPV in garages

Field trials

Returning from the garage tests began to think how to continue to experience. Although what is there to think, the range must be checked. So on Monday they made a test in a real field. True, the test was without flight. The ground part, the plate, the laptop and the glasses, stood still, and the “side part”, twisted with electrical tape for convenience, was taken by car to a previously measured distance and watched what happened.

Volunteer Lyokha, volunteered to help in the tests :-)





This time the entire video stream was recorded simultaneously with playback, so there is a “live” video. We checked two distances, 700 meters and 2200 meters. At 700 meters there was a full-fledged direct visibility, they saw where to direct the plate. But where there is 2200 meters - our mobile side part was no longer visible, the bush got in the way, so it was suggested at random, guided by the LED indication of the signal level on the plate.

In addition to the "digital link", a mobile team drove a model of a helicopter, on which stood the usual analog video transmitter. As a result, when it was turned on, the digital link immediately began to fool. But fooling in different ways, the impression was that there was a dependence on the mutual arrangement of the Picostation and the analog transmitter. In addition, it turned out that our plate was too narrow, the slightest deviation to the side led to a loss of signal or a sharp deterioration. In the following tests, we will change the plate to a “bullet” - Ubiquity Bullet M5 HP with a powerful omnidirectional antenna, or the same, but 2.4 GHz. At the same time, and Picostation should be changed to M2 HP.

But so far it happened - it happened. We make a discount on the fact that it was difficult to direct the plate all the time, the plate was on the ground (and it would be better to lift it higher), the bushes were in the way. I still can not believe that the following videos are just a recorded stream, and not taken on a regular camera :-) And so it is, it was the RTP H.264 stream that GStreamer received, displayed on the screen (and then with glasses ) and write to the file.

Control record for measuring the minimum delay

Circuit improvement options

In general, the weakest link in the resulting scheme is Wi-Fi, but it also has advantages. The advantages are that it is widely distributed, two-way (that is, reception and transmission are possible at the same time), it is possible to drive video and telemetry from one side to the other under the same connection, and control from one side to another. At least, the control of the camera suspension can now be implemented without any problems, so that the same Virturile will twist the servo of the suspension.

Another plus - you can try different routers, different antennas. There are also boosters, but this complication of the scheme begins. There are suspicions that with real flight between the ground and onboard parts there are fewer obstacles than on the ground, so the range should get better. In general, the following tests will be on the Hexacter and Skywalker type aircraft in the field. And no more plates on the ground.

You also need to add a change in the video bitrate depending on the signal level. This is easily implemented on Virtuirka using the gstd daemon.

OSD

The first question I was asked by the guys from Garage # 17 was a question about OSD. Those. information about the various parameters of the state of the side. Voltage, roll, pitch, distance from base, coordinates, azimuth, etc. Usually, all this information with the help of special devices is superimposed on an analog video image and transmitted to the ground by a video transmitter. Accordingly, the received video cannot be cleared of this information. And the information can not be processed in any way, except visually.

With a digital link, it is immediately possible to drive telemetry as a normal data stream, regardless of the image. And on the receiving side already process it as you like and, if there is a need to see it in glasses, overlay the video. But not in the video itself, namely to draw the top layer on the screen (monitor, TV, glasses, whatever). Or feed it to ready-made applications, like MIssion Planner.

I tried Virturilka to determine the voltage of the on-board power supply (via a voltage divider connected to the ADC input) and transmit the received information via UDP to an application running on a laptop that accepts video. Everything is perfectly transmitted and displayed, plus it all turns out to be interactive (you can turn off the display of information, switch the ADC channel or create something else). A small demonstration with the first breakdown of such OSD can be found here .

But then another problem appeared. To transmit telemetry to the earth, you need to get data from somewhere. You can, of course, connect a scarf with gyroscopes, accelerometers, a barometer, a compass, a GPS, etc. etc. But why, if, for example, these sensors are usually already on the copter, it is necessary to “only” take their readings from the flight controller. This is where I stalled - I don’t know if common copter brains have such an opportunity. If there is - then the problem is solved.

3D Stereo

Appetite comes with eating. After it turned out that the transfer of HD video with an acceptable delay for slow flight is still possible, I wanted more. How to get a stereo picture?

The option "in the forehead" - to put on board two Virtuurles, two cameras. But the flow of drive through the same router (Picostation). Here you just need to find a compact passive hub / switch. Or do it yourself, since there are many chips for this business.

Again, in order not to copy-paste myself, I give a link to the testing of such a bundle , maybe someone will be interested.

The disadvantages of this option are obvious (in addition to a double set of all the iron, except for the router) - twice the flow. This can be avoided by combining the images from the two virtualulok on board. Those. one Virtirlka master, the second - the slave. The master takes the stream from the slave, combines and transmits to the ground. This is not even a theory; such a bundle has already been implemented by an office called RidgeRun. Based on these elements for GStreamer -
github.com/RidgeRun/gst-plugin-usb
github.com/michaelgruner/gst-plugin-anaglyph

Only here their pictures are combined in anaglyph, but I still want a full-fledged pair of independent pictures for the left and right eyes. Although there is already a question - how to watch it all ...

Non-analog counterparts

Discarding solutions that are not readily available to an ordinary modeller because of the wild price tag, only one option remains. Most recently announced by the Chinese DJI Lightbridge . As I understand it, there is not Wi-Fi, but just an OFDM transmitter and receiver, although I could be wrong. A delay of <80 ms is claimed, however, in the video taken by one of the owners, it is clear that the lag is 200-300 ms, i.e. not better than I got on Virtuerke.

Here is the video with a demonstration of the delay DJI Lightbridge. See on timer.

About the lag of the display was discussed all in the same thread on the design . In any case, the price of this lightbridge is around $ 1,300. How much will it cost in Russia - I'm afraid to imagine.

Conclusion

Here is a description of a series of tests turned out. Of course, much remains to be experienced in practice, but the fact that flying on a copter or a plane wearing glasses with full-fledged HD video is already pleasing. Oh, I am exactly happy :-) And when we complete the HDMI input (we have already delivered test samples into production), then GoPro can be connected as a full-fledged exchange rate camera.

In general, if someone who has read this opus wants to see the current set of hardware in action - well, at Hobby Expo 2014 . We will participate there , just show HD-videos from copters and from large R / C-machines. And the glasses that I mentioned in the topic will be on our stand.

UPD: I forgot to write about Yota. LTE coverage is getting better and better, we should try to drive the video through Yota (Megaphone, Beeline, MTS) in the field.

UPD> For comparison of dimensions - a regular lighter, virtual and naked Picostation M2 HP alongside



Total consumption during HD streaming at 12 Volts is about 400 mA.