Replies to This Discussion

Permalink Reply by Kirill on October 16, 2011 at 11:15am

I have made a few test flights with 2.048 today. It was a little windy outside.

The copter is much stable, than previously, however it was always osclillating a little. Here is a video:

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Permalink Reply by Helldesk on October 16, 2011 at 2:45pm

Perhaps try reducing your Rate roll and pitch P values to stop that oscillation?

Arducopter PID tuning how-to video

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Permalink Reply by Kirill on October 17, 2011 at 8:45am

Ok, I'll try. Thanks.

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Permalink Reply by Grips on October 16, 2011 at 4:00pm

I do have three questions, the first two a bit practical:

 

With regard to the GPS position hold using a mediatek GPS module. How often does the GPS receive an updated signal from the satellites?Would it be easier to have two mediatek's on board and take an average reading from two? Or as I presume this is already done by multiple satellites?

 

In the context of a 'loiter', be it the copter moving around a point in approximately a 2-3m circle/box. The point that the satellite chooses, how big is it? I presume that the 2-3m range could be the point the satellites provide? Its completely understandable why the public does not have more accurate GPS devices, I am not debating that whatsoever. Every position the GPS receives, how much error is there?

 

Another note: I put a small round band-aid over the baro and it appears that it limited the vertical movement during alt hold to around 6ft. One like this

Third and Last. I use a Dx6i. Is it possible to do the channel 6 tuning with that? I have looked in the WIKI but cannot find where to setup this? I know that you need to do it through the compiler but that is the extend of it.

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DeveloperPermalink Reply by Olivier ADLER on October 16, 2011 at 5:02pm

 

"How often does the GPS receive an updated signal from the satellites?"

 

The reception is continuous. The output frequency update depend only from the computing power of the GPS unit. There are GPS units with 100 Hz output for military or scientific use.

 

"Would it be easier to have two mediatek's on board and take an average reading from two?"

 

No, they would receive exactly the same error. The only interrest of this is when you need to get a heading without moves. In this case, it is possible to have dual GPS units, or a GPS unit with dual antennas and two acquisition circuits, to compute a heading. 50 cm between antennas can be enough to get about 1 degree precision. Those special GPS are used for directive antenna heading setup and for big boats navigation.

 

The best GPS precision is about 1m in the horizontal plane, and it is worse for altitude. This is for L1 receivers with normal acquisition time, WAAS corrections and very ideal satellite reception. Using expensive L1 - L2 (dual frequencies) receivers, extending the acquisition time to a few minutes, and using a more complex algorythm using satellite signals phase information, it is possible to get a couple millimeters precision. But be prepared to spend between 3000 and 20 000 $ for the GPS receiver. And this work only if the GPS is fix. It is possible to get a better precision for roving GPS (a few centimeters), but it needs again expensive GPS receiver with special and very proprietary algorythms. This is used for dozers or tractors for example.

 

If the spatial program is not restricted because of actual economy problems, we could get in a few years L1-L5 GPS receivers (2015 - 2019 ?), giving a few centimeters precision for the same price as today normal L1 receivers.

 

 

 

 

 

 

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Permalink Reply by Helldesk on October 16, 2011 at 8:55pm

Not to mention using GPS together with Galileo and GLONASS satellites to calculate even better accuracies since you can then see a much larger satellite constellation at any given time. This should be possible in the coming years.

Waiting for light to get another flight done on 2.0.49... :)

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Permalink Reply by afernan on October 16, 2011 at 10:33pm

BTW:

first two Galileo satellites will be launched this week with the first Soyuz launch from French Guyanne. (I´m working on that). You can follow the launch by internet thru Ariane web page. : it will be exciting!

 

Liftoff is scheduled for Thursday, October 20 at exactly:
07:34:28 am local time
10:34:28 UTC
12:34:28 pm in Paris
06:34:28 am in Washington, D.C.
03:34:28 pm in Moscow

 

Angel

 

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Permalink Reply by Helldesk on October 17, 2011 at 2:40am

Yes, I follow rocket launches. Exciting times! Do you work on supporting the launches in French Guiana or the satellites (or their systems) themselves?

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Permalink Reply by afernan on October 17, 2011 at 5:38am

Yes. I work in ASTRIUM Spain (an EADS company). We supply systems and parts for different launchers (Ariane 5, Soyuz, Proton, Atlas, Vega, Rockot, etc). I use to go to french Guyanne. Next time I´ll bring my quad with me to make some video. In fact, EADS has other division dedicated to drones different sizes, mainly military, but I work in launcher mechanical structures. 

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DeveloperPermalink Reply by Olivier ADLER on October 17, 2011 at 1:31am

 

True, actual high end GPS receivers used in the GIS area (Geographic information systems) are able to do this and recent ones are able to receive the new L5 civil channel.

 

 

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Permalink Reply by Jose Angel on October 17, 2011 at 12:38am

From this rcgroups post about the DJI Wookong-M copter I read the following:

The entire GPS setup is driven by an Atmel SAM3 Cortex-M3 processor 

It seems to refer to a dedicated processor different than the autopilot processor.

And also I think that openpilot plans for gps add-on are based on a dedicated cortex for the GPS too.

 

From my ignorance, what type of algorithms could be executed on a Cortex processor for improving the gps signal?

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DeveloperPermalink Reply by Olivier ADLER on October 17, 2011 at 1:18am

 

I think that the Cortex does not enhance the GPS signal. It would not be powerfull enough. The GPS can output raw carier-phase and pseudorange informations in a special format (for example Rinex) , but it is very heavy and complex to post process those informations in realtime.

More to get this working, you need a special GPS with enabled Rinex or similar output. Quite expensive.

 

I think that the Cortex is here for navigation purpose.

 

 

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