Replies to This Discussion

Permalink Reply by Ramesh Tahlan on May 25, 2012 at 6:49am

Bradley.

I dont have a sonar, but logically, even when the sonar is pointing downwards, it does get certain reflections upto a articular angle in all directions, as all radiations have a polar diagram of returns, which it processes and takes the least time return signals.... so upto a certain amount of roll, should not be a big problem, but beyond a certain roll angle, yes, an error will occur. what is that roll angle limit, i guess the DIY guys will have to tell us..... cause i am also planning to put a sonar soon....

Permalink Reply by Crispin on May 25, 2012 at 6:52am

The sonar has a limit of about 8m. If you are near this or indeed roll far enough, that 8m limit would be broken and there would not be a return (both from distance and the fact that there might be nothing reflected back). I assume it would then switch over to baro which, depending on the version of AMP, might be quite different. 

I would assume (yes, lots of that) that the APM would take into account what the height is based on roll, assuming of course, it has a valid return signal. See the Optical flow description for pictures of what I am babbling about: http://code.google.com/p/arducopter/wiki/AC2_OptFlow

Having a look at your graphs (I'm no expert, just surmising) it looks like you're at the edge of what the sonar can do.  If you disable the sonar, can you still (within reason)  Atl-hold. 

Permalink Reply by Bradley J Carr on May 25, 2012 at 6:55am

I will have to do that.  I thought the sonar I had was good for more than 8m.  But I could be wrong.  When i was flying in simple mode and using the alt_hold it was dipping.  When i was flying around it would dip.  Now just loitering it would keep reasonable alt hold.

Permalink Reply by Crispin on May 25, 2012 at 7:01am

You could have noise on the sonar. There are a number of ways you can eliminate that. There is an entry in the wiki IIRC. Using twisted sonar cables is also a good idea. The sonar could be affected by many things but overall, it should be ok. 

I noticed last night that mine rose in blips but always dropped back to original level. I must have been 5-6m above a tarred road so pretty decent surface. 

Some put microphone sponge over the sonar to reduce wind noise. Not tried it myself though.

Permalink Reply by Ramesh Tahlan on May 25, 2012 at 7:07am

Crispin.

from the link u give for optical flow..... i notice that it can now be used with apm 2,,,, i read in the biggining when apm2 was launched that optical flow cannot be used with apm2, So we can use optical flow with apm2 now, is that correct.

regards

Permalink Reply by Crispin on May 25, 2012 at 7:12am

In 2.5.5 it is (apparently) supported.

I ordered one the same time as I ordered my APM2 and was gutted to find out they cannot be used :( With the new shiny 2.5.5 they are supported so I broke out the soldering iron and got connecting only to find out that my sensor was toast :( It worked with a friend's sensor but did not fly with it.  The good folk at UnMannedTech are replacing it as we speak :D

Permalink Reply by Bradley J Carr on May 25, 2012 at 8:01am

On the graph would you see the noise?  How can I test to see if I have a noise problem?

Permalink Reply by Crispin on May 25, 2012 at 8:05am

I'm not a pro but I would say it does look like you might have a noise (or erratic read?) problem. See your green line, it looks like you were above what the sonar could do but the drops and spikes in it could be noise. I'm not sure of the duration of the graph, that could be we you descended or could be noise.

Do another flight over a solid surface and see the graph after, are there large dips or spikes in the graph which where not there in the flight?

Permalink Reply by Bradley J Carr on May 25, 2012 at 8:07am

I will have to try that.  I really don't have a good smooth hard surface.  Then only thing I have out here is grass and wheat fields. At the end of the graph is were the copter was going down.

Permalink Reply by Crispin on May 25, 2012 at 8:15am

Grass should be fine, wheat might be a bit erratic. 

Interesting though that you say the end of the graph is where it is going down - I would have expected the sonar alt to be near zero (think it will zero if it lands on it's head as well). 

Could you have been flying with low batteries? I've seen my quad behave oddly when the batteries are running low. Struggles for lift but also struggles for balance. Reason I ask, and I could be misreading this, is that the baro starts to decrease and then just stops. The climb-rate is positive but your throttle also dips below zero.

Your throttle increases but it is still sinking and then everything just stops. Could it be brownout and then eventual APM reset due to low power?

Permalink Reply by Bradley J Carr on May 25, 2012 at 8:20am

No, I always go out with fresh batteries.  I have learned this from flying airplanes.  There is a video.  The copter was crusing to its first way point and then it took a sharp turn left and then a sharp turn back to the right.  Then when trying to comback is when the it lost altitude and tried to level out and never could recover.  I picked it up right after that happen and flew in simple mode just for giggles.

Permalink Reply by Bradley J Carr on May 25, 2012 at 8:22am

You can see in the video, it really tried to get back to level but it was to late, it was losing altitude really fast.

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