Tag Archives: FPV

RC Almost Finished

Here’s the case after my best attempt:

 

It looks… bad. The paint coat is horrible and full of scratches and the screen is too big.

But worst of all, the screen is not bright enough in direct sunlight. Not even close. I don’t have a photo but after brief testing I’d say it’s unusable.

So I’m pretty disappointing with the result – I ended up with a big, heavy RC system that is too dim to be usable for FPV.

I searched for a week for alternative capacitive touch screens, preferable in the 5-7 inches range but found nothing bright enough under 100 euros.

So after a mild diy depression I got an idea that will solve at lease 3 of the issues – cost, bright screen and the RC size: use my Galaxy Note4 phone as the screen.

The setup will look like this:

  • The quad will send video through 2.4Ghz, packet injection (a.k.a. wifibroadcast method) and RC stream through 433Mhz
  • The RC will receive both video and RC data and relay them to the phone using another 5.8Ghz wifi UDP connection. The phone will decompress the H264 video using OMX (or whatever is available) and display it with telemetry on top.
  • The phone will also act like a touchscreen interface to control the RC/Quad

 

Basically this is what most commercial quads (like Mavic) are doing. I’m sure the video link is 2.4GHz due to longer range than 5.8 and better penetration and the connection with the phone is done over a 5.8, low power link.

 

So the next steps are:

  • Redesign a smaller case that will accomodate a Raspberry Pi 3, the RC stick and fader + buttons and wifi cards
  • Write a quick android application that can connect to the RC and decompress the video stream
  • Profit!

Video Latency

Just did some latency tests using RUDP through wifi, 640×480@30fps, 2Mbps.

Both the laptop and the quadcopter are in the same room but they go through a router 3 walls away. Signal strengths are (as reported by iwconfig):

Quad:
Link Quality=70/70  Signal level=-37 dBm

Laptop:
Link Quality=58/70  Signal level=-52 dBm

Ping reports these RTTs:
64 bytes from 192.168.1.110: icmp_seq=1 ttl=64 time=137 ms
64 bytes from 192.168.1.110: icmp_seq=2 ttl=64 time=160 ms
64 bytes from 192.168.1.110: icmp_seq=3 ttl=64 time=85.4 ms
64 bytes from 192.168.1.110: icmp_seq=4 ttl=64 time=108 ms
64 bytes from 192.168.1.110: icmp_seq=5 ttl=64 time=125 ms
64 bytes from 192.168.1.110: icmp_seq=6 ttl=64 time=149 ms
64 bytes from 192.168.1.110: icmp_seq=7 ttl=64 time=73.6 ms
64 bytes from 192.168.1.110: icmp_seq=9 ttl=64 time=119 ms

The quadcopter uses the more sensitive alfa card while the laptop has its own crappy RTL8723be card that has many issues under linux…

I happen to live in a building with a very noisy wifi situation so SNR is not good at all.

Average latency is around 100-160ms with random spikes of 3-400 ms every 10-20 or so seconds.

[Edit – just realized that both the brain and the GS are debug versions…]

To measure I pointed the raspicam at my phone’s stopwatch app and then took photos of the phone and the screen at the same time. Here are some of them:

20141128_212006

 

 

 

 

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20141128_212007