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Re: [Paparazzi-devel] Port airborne code to Linux

From: Achim Walther
Subject: Re: [Paparazzi-devel] Port airborne code to Linux
Date: Tue, 10 Mar 2009 13:51:22 +0100

> Cool. Do you have a website where I can have a look at your aproach and
> learn from it?

Well, the info is somewhat distributed among several pages.
- the current airframe:
- a post to the German RC-Line Forum about the latest status:
- the current airborne software in a simulation loop with FlightGear (including 
autonomous landing of a 737 ;-):

If not already implemented, the Paparazzi project could benefit from the 
software-in-the-loop aproach as well. Be it FlightGear or X-Plane - they both 
have an UDP interface to be used for UAV testing.

> As I am using OLSR-mesh-networking I for example get relaying of downlink-
> messages from one drone to another (others on weels or stationary) to
> nodes of a local Freifunk-Community over the internet to the GCS for free.
> Think drones or drones and Freifunk-activists acting together. Now that
> sounds like a fun field of research to play in. :)

Oh yes, there are certainly a lot of things to explore.

> Can you tell me more about your setup and the GPS-interferences?
> Where did you place the GPS-antenna and what antenna did you use?
> Are you using the GPSstix?

I'm not using the GPSstix yet, just the Basix with a customized motherboard. 
The GPS (ublox SAM-LS) is about 10cm away from the Gumstix - perhaps too close. 
The GPS sometimes shows problems to detect satellites after a cold start. It's 
OK once airborne.

> I don't see much added weight and power-consumption so I don't actually
> care
> about not using the full potential of the platform
> as long as it also gives me the highly advanced communication- and
> sensors-
> possibilities the board has compared to a bare-bones microcontroller.

Well OK, it's always good to have a big reserve of computing power. I mentioned 
the advantage of Linux as a prototyping environment. But I don't see the 
Paparazzi project still in a prototyping phase. Therefore only the necessity 
for computationally intensive and / or networking software will justify the use 
of Linux for Paparazzi.

> Of cause I'm using a very stable and slow airframe (trying to get
> fully autonomous landing using ultrasound working some day) so I don't
> concern myself with anything below a tenth of a seconds like a helicopter
> would need to.

My current approach is a two-process architecture where the child process is 
responsible for reading the GPS and forwarding the position information to the 
parent process via shared memory. The parent process reads the IMU in a 50 Hz 
cycle. What I'm worried about is the context switches between the processes. 
But I haven't looked into that very deeply. And as you say - it's a software 
issue that can be solved.

> Marcus

Regards, Achim.
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