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Permalink Reply by agmatthews on July 16, 2011 at 6:09pm

Attached is the log files from the full flight tests

Attachments:

• AC2 Log 160711.zip, 810 KB

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Permalink Reply by agmatthews on July 16, 2011 at 6:26pm

Looking in to the data further reveals that the 'pulsing' or 'gunning' behaviour in Alt_Hold can be clearly seen in the throttle trace in the image below at the point I enter Alt_Hold mode (about line 10500) and the peaks and troughs in the throttle correlate with troughs and peaks in the noisy sonar data. ie when the sonar drops out the motors throttle up. Note the pink line in this graph shows when flight mode is Alt_Hold

It appears a number of others users have seen this behaviour either sonar drop outs or Alt_Hold pulsing and lack of holding.

http://diydrones.com/forum/topics/altitude-hold

http://diydrones.com/forum/topics/arducopter-2034-preview?commentId...

Do we have a systematic problem with sonar hardware or software, or could it be an obscure combination of the two?

 

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Permalink Reply by agmatthews on July 17, 2011 at 2:03am

Some reading and thinking has lead me to wonder if there is RF or electrical noise interference or if the battery connector may have been moving in and out of the filed of view of the sonar sensor.

I have extended the sonar mount legs by 15mm with additional plastic stand offs and ensured the battery connector is secured out of the way.

I've then run a test of the sonar with the Arducopter captive in my outstretched hand, with and without the motors running.

The first peak in the image above is with the motors off, the second peak is motors running

The step in early part of each peak is me carefully climbing up on a chair while holding a live Arducopter

The results are much better than before with only the odd 'spike' which could be explained by a stray leg or similar entering the sonar sensor field of view. There is more 'noise' in the second peak - with motors running - but nothing like before.

Time to test fly the new mounts. And see how Sonar and Alt_Hold performs. It's Sunday night here downunder so this will have to wait for another clear calm winters day.

One question I now have is about the scaling on the sonar data the values shown are 150% of what they should be. from the Maxbotics specs sheet the scaling factor changes by 150% depending on what voltage you supply the sonar module. Time to read the circuit diagram and code to check things out.

 

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DeveloperPermalink Reply by Olivier ADLER on July 17, 2011 at 2:44am

 

The sonar has a very large field of view. It must be mounted far from the frame, it can have about 180° filed of view at near distances !

 

You can verify this putting your fingers around it and checking it in the cli.

 

It must be mounted with a small plate around, so that it does have a more focused  filed of view. A one inch (2.5 cm) plate is a minimum diameter for the plate.

 

Watch for the sonar datasheet, where you will find filed of view sensitivity according to plate diameter.

 

 

 

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Permalink Reply by u4eake on July 17, 2011 at 3:18am

Hi, My donar data looks exactly the same in my logs and my alt_hold in 2.0.35 was also not working (constantly climbing or descending).
I have the EZ0 sonar mounted about under the forward arm, halfway between centerplate and motor, with a piece of foam between the arm and sonar.
Please let me know if modifying your mount solved your problem.

JMD45, you mean we should put a small cilinder around the sonar ?

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DeveloperPermalink Reply by Olivier ADLER on July 17, 2011 at 3:41am

 

Yes, i think it is better to reject side interferences.

 

 

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Permalink Reply by agmatthews on July 17, 2011 at 5:11am

JMD45,

This is exactly the mount I am using

Here is a photo of it with the extra 15mm M3 standoffs to lower the sonar

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Permalink Reply by u4eake on July 17, 2011 at 5:13am

Is that lower ring for protection against impact or is it for narrowing the beam ? Should I use a cilinder around the sensor or a ring to focus the beam ?

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DeveloperPermalink Reply by Olivier ADLER on July 17, 2011 at 5:19am

 

I think it does avoid two much sonic refraction around the sonar. So that reflected interferences does not enter from behind.

 

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Permalink Reply by agmatthews on July 17, 2011 at 5:26am

The lower ring is structural. It protects the sonar transceiver from knocks.
If you look closely you will see the black transceiver sticks down a millimetre or two below the lower acrylic ring. My reading of the maxbotics specs sheet is that anything in the field of view may cause a signal. I would not recommend any sort of cylinder around the sensor.

This mount is from Jani at Jdrones http://store.jdrones.com/product_p/mntmax120.htm
The extensions I've used are also from Jdrones http://store.jdrones.com/product_p/hxs315fm.htm

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Permalink Reply by agmatthews on July 17, 2011 at 5:11am

u4eake,

Could up upload a log so we can compare?

-Andrew

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DeveloperPermalink Reply by jasonshort on July 17, 2011 at 10:29am

Looking at those values in the log. It seems impossible with the moving average filter that's in the Rangefinder class. Something must not be working right. I'm looking at it today.

Jason

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