Electronics > Projects, Designs, and Technical Stuff

Digital FPV video for drone racing

<< < (14/28) > >>

OwO:
I would start by implementing something simple like a JPEG stream over BPSK. Cameras like the ov2640 have JPEG compression built in which means all you need to do is buffer up the data and modulate it (and add some FEC later on). You can output the BPSK signal on a single digital pin on the FPGA which means no DAC needed.

For the receiving side I'd experiment using a PlutoSDR or LimeSDR, decoding the signal on the PC initially. Once you have the modulation scheme worked out you can implement the receiver on the FPGA of the SDR.

Marco:
Actually I think the best signal to generate first would be a NTSC signal.

I misunderstood the RTC6715, I thought it only brought IF out, but there's also another FM demodulator in there ... so I assume the IF just loops back around the outside to allow for filtering ... Oops. The mobile phone fpv receivers make a lot more sense to use than the modules I mentioned before I think. The NTSC test signal can be used for tuning the receiver, before you start a digital data stream which will probably make the automatic tuning barf.

So with that the hardware I would use ... Nanopi Neo Air or Banana Pi Zero with a OV5640 camera for the transmitter, some other SBC with a LCD connector for the receiver (for prototyping you could use a laptop running Linux with preempt_rt), ROTG02 receiver, TLC7528 DAC, AD9200 ADC and EZ-USBĀ® FX2LP to create a buffered connection between the SBCs and the ADC/DAC. All in all a rather substantial project getting all that to the point of even being able to communicate.

ogden:

--- Quote from: Marco on January 21, 2019, 01:37:55 pm ---So with that the hardware I would use ... Nanopi Neo Air or Banana Pi Zero with a OV5640 camera, ROTG02 receiver, TLC7528 DAC, AD9200 ADC and EZ-USBĀ® FX2LP to create a buffered connection between the SBCs and the ADC/DAC. All in all a rather substantial project getting all that to the point of even being able to communicate.

--- End quote ---

So you are suggesting to make video compressor, >= 6Mbps TX/RX modem(!) with FEC(!) out of Nanopi Neo Air or Banana Pi Zero. Also radio of choice is receiver with specs/description "It has low latency around 100ms" :D

Marco:
Yes, a 6 MHz datastream isn't really a huge problem for a 1.2 GHz 4 core processor.

The receiver has a NTSC->USB digitizer, that's where the latency comes in. You simply tap a line on the PCB, that 100 ms latency doesn't affect you.

IDEngineer:
Been watching this thread with interest while on the road and unable to comment.

My son is an internationally ranked drone racing pilot (as just point of reference, he's 1st Place member of the five-person TeamUSA that represented the United States at the IOC-sanctioned World Championships in Shenzhen China a couple of months ago). Video problems are the NUMBER ONE ISSUE in this sport. We talk about ways to address that all the time. We've considered quite a few of the things discussed in this thread.

I'm thrilled that this topic has generated so much interest here. The thing I want to share with everyone - from the direct hands-on perspective of a top-ranked pilot and the literal embodiment of the target market for such products - is that latency is your single most important criteria. Many times at competitions my son has sacrificed video quality to reduce latency. In fact, he flew with B&W-only video for a while because with the cameras and electronics of that era it reduced latency by a pilot-noticeable amount. He also suffered the loss of a qualifying round at Nationals in Reno NV in 2017 because the venue-provided diversity system had so much latency that he and other pilots could not control their aircraft; most of the top pilots switched back to their own gear, enduring the multipath and quality problems to get responsiveness.

If you haven't done this yourself, it's hard to realize just how important low latency is. Most of the world-level racing drones are spinning ~5 inch props on ~200-300mm frames, and on straights they'll hit 80+ MPH heading toward split-S turns that peak 150+ amps (not a typo!) from their 6S LiPo packs. The gates they're shooting for are sometimes only 5x5 feet, and when you're approaching at 80 MPH tens of milliseconds really do count.

There is "tribal lore" in the FPV industry right now that compression cannot be done because of the inherent latency. My son and I have a different opinion and think it's possible by thinking a bit outside the box, but my point is that the industry is so intensely focused on low latency video that everything is analyzed with that in mind.

I'm excited about this thread and where it will hopefully go, but wanted to offer a little guidance about what's important as it moves forward.

Thanks!

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod