Which Maxbotix sonar should be the standard?

    About two months ago we added altitude hold using the Maxbotix sonar to the ArduCopter (you can find instructions re how to set it up on the wiki).  At the moment on the we recommend the LV-EZ4 and XL-EZ4 but that's not based on a lot of research or experience so the question to the community is:

            Which one of the Maxbotix sonars is best for our purpose?  


     Above you can some pics extracted from the datasheets of the four sensors.  Each is a 1 foot grid and shows the theoretical range within which the sonar can sense a 3.5 inch pole (look at the black lines, not the red dots)


     The first choice is whether the extra cost of the XL over the LV is worth it - according to the data sheet the XL's range is 80% better (nearly twice the range) which makes me think "yes".
     The next choice (for either LV or XL lines) is between the EZ0 (fat-beam but longer range) or EZ4 (narrow-beam but shorter range).  We went with the EZ4 because we thought the narrow beam would make the altitude correction using roll/pitch work better but I guess we might be able to correct for the fat-beam of the EZ0 in the code and then we'd benefit from the longer range..but perhaps we would also get more false readings?
     So my guess is it should be the XL-EZ0 or LV-EZ0 but it would be great if people especially those who have played with sonars could voice their opinion/experience.  Also at least one person has had trouble with the XL-EZ4 over carpets and grass so if people have experience over various surfaces we'd love to hear about it!

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Comment by Ritchie on February 27, 2011 at 4:31am
For the basic purpose of ping response I think the range needs to be 10ft at least. I personally believe the AE version is far superior thanks to the analogue output of the ping response but its useless for altitude hold without further processing.
Comment by DaveyWaveyBunsenBurner on February 27, 2011 at 4:37am
I know you said not to look at the red dots but the XLEZ0 looks interesting on 3.3v no? Not much wider than LVEZ0 on 5v but a very useful range???
Comment by Christof Schmid on February 27, 2011 at 5:39am
I was flying a Parrot AR.Drone lately. Their altitude hold (tested 50cm to 4m) is very precise over different grounds (Carpet, Stonefoor, Gymhall). I did not try grass/high grass yet. Maybe we could find out what they are using.

3D Robotics
Comment by Chris Anderson on February 27, 2011 at 7:28am
Christof, all of the sensors mentioned above are excellent on hard floors and short carpet. But over grass, they really struggle. My own experience with the AR.Drone over grass is a bit better, but it too is not as precise as it is on floors. Given that ArduCopter is designed for outdoor use and the AR.Drone is primarily designed for indoor use, we'd probably want a different solution.

Comment by John Church on February 27, 2011 at 8:59am
Just chiming in- I am having great success with the LV-EZ0.  Hold is steady and the beam width, in reality, does not seem to be the 6-7 ft. that the datasheet suggests and the quad only responds to objects directly beneath the airframe. Without experience with the other models, LV-EZ0 gets my vote because of the satisfactory performance and good price.
Comment by Jack Crossfire on February 27, 2011 at 1:22pm
Personally hate Max in general because theirs is the only algorithm which can do it in a single transducer & it's heavily patent protected, so you can't integrate a cheaper version in your own main board & sell it.
Comment by Tero Koivunen on February 27, 2011 at 1:55pm
Is it the max range anyway about 6.45m with LV-EZx? Detecting ground etc "quite" big.

Comment by Randy on February 27, 2011 at 7:00pm

@Ritchie (right at the top of the thread),

     to be clear the AE is the same as the XL (i.e. the more expensive one) although there's some comments here about the AE not having PWM output (which we don't use anyway).  There's no other differences right?

Comment by Randy on February 27, 2011 at 8:09pm

@John Church,

      great to hear this kind of feedback.  The LV-EZ0's range according to the datasheet is more like 12feet (maybe you were looking at the LV-EZ4?) but it could be longer than shown as the datasheet info is for detecting a 3.5 inch wide dowling instead of the ground.

Comment by John Church on February 27, 2011 at 8:45pm

Hi Randy,

The detection length is close- effective to around 12' as the diagram illustrates. It's the width that seems narrower than described. I'll play a bit and see how the height effects the width of detection in real life- up until now my tests have been at 7'+ .


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