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Digital FPV video for drone racing

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TheDane:

--- Quote from: IDEngineer on January 22, 2019, 06:56:53 pm ---* The camera and its transmit-side electronics must be physically small and weigh well under 100 grams. A particular camera with which I'm familiar is 74 grams and considered grossly overweight by most pilots. Total aircraft dry weight is generally around 300 grams including video system, of which the four motors alone are 100-120 grams.

* Establish a low latency network (50mS is about the max) on an ISM band (so no licenses are required) that can support at least eight simultaneously active pilots.


--- End quote ---

http://socialcompare.com/en/comparison/raspberrypi-models-comparison
Raspberry Pi Zero W - without headers: 9 grams
Raspberry Pi Zero WH - with headers: 12 grams

Some random 5.8 GHz AC WiFi high speed dongle - https://www.amazon.co.uk/Daffodil-Ultra-Fast-Dongle-LAN05/dp/B016QKQ1U0#productDetails
Weight: 9 grams

5.8 GHz WiFi band is ISM, and has ping times at/below 1 mS if done correctly  ^-^

I do not know if the Raspberry Pi is good enough to handle video encoding at breakneck speeds - fortunately other SBC's exists that does not use Broadcom , such as the Beagle Bone(s)
(I have not used those to video-encode, so I can't comment on it's usability):
https://www.mouser.com/new/seeedstudio/BeagleBone-black-vs-green/
The TI SoC has a Programmable Real-time Unit (PRU) - making it excellent for controlling hardware pins, timing, transfers, etc.
It is large (it is a development board) - its weight is around 40 grams.

I would say hardware wise, it is not impossible - it should be rather light, inexpensive, and easy to obtain.
Software - well, can't help you there

Edit - clarify "5 GHz band is ISM, and has ping times at/below 1 mS if done correctly  ^-^"

ogden:

--- Quote from: TheDane on January 22, 2019, 06:42:56 pm ---Doing a partial frame update/interlacing - is like filling a FIFO buffer, and only rendering the final picture frame when full. Great for slow/non-moving stuff.

--- End quote ---

Most digital video sensors works same "scan line" way as oldskool TV - readout happens line by line. At 640x480 @ 60fps analog tranceivers will have roughly 1/60 sec = 16.666 msec "delay". Proposed 8-line buffer will add 8 * ( 1/(60*480) ) = 0.2777 msec delay. To me 1.66% frame time increase due to 8 line buffer does not look like much. Assuming that existing analog transceivers are ideal giving 16.66 msec best case latency, for digital video we use 120 FPS so summary interframe time + buffering delay is (16.666 +  0.2777)/2 = 8.472 msec. If we add kinda pessimistic 1 msec digital radio delay (doable even with WiFi), total latency is 9.472 msec. One is clear - radio is not the main contributor to (perceived) latency.

IDEngineer:

--- Quote from: ogden on January 22, 2019, 07:20:59 pm ---One is clear - radio is not the main contributor to (perceived) latency.
--- End quote ---
Agreed. The discussions of latency here have centered on various proposed data processing steps such as compression to obtain higher resolution, or FEC to handle RF dropouts. Today's pure analog systems certainly don't have much in the way of processing latency, AFAIK they don't even buffer a line - it's as real time as the semiconductors make possible.

TheDane:

--- Quote from: ogden on January 22, 2019, 07:20:59 pm ---
Most digital video sensors works same "scan line" way as oldskool TV - readout happens line by line.

One is clear - radio is not the main contributor to (perceived) latency.

--- End quote ---

One thing is the sensor, another is the display.
The sensor output is 'serial' - the display output is 'not'.  I hope you get where I am pointing at, as the screen has to be 'stationary long enough to show the entire picture', and then show the 'entire next picture long enough'

I too agree on the radio tech being fast enough.

Edit: Adding info:
Oldschool TV's/CRT work 'in serial mode', however the screen used phosphor which has a persistence glow, thus 'keeping the image on screen'
https://en.wikipedia.org/wiki/Cathode-ray_tube#Phosphor_persistence

ogden:

--- Quote from: TheDane on January 22, 2019, 07:26:25 pm ---One thing is the sensor, another is the display.
The sensor output is 'serial' - the display output is 'not'.

--- End quote ---

Are you sure? :)

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