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Permalink Reply by Rick Eis on June 1, 2012 at 5:58am

So what is it in the code that is limiting the distance for the sonar?

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DeveloperPermalink Reply by R_Lefebvre on June 1, 2012 at 6:00am

Rick, I believe the 20cm limit is actually built into the sonar.  It can't measure less than that, so it never reports less than that.

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Permalink Reply by Rick Eis on June 1, 2012 at 6:09am

OK...so as far as you know the sonar should be able to keep our copters locked in then near 20 or 30cm?  Or is there something else limiting the capability at this minimum elevation?

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Permalink Reply by Jake Stew on June 1, 2012 at 9:10am

Sonar is cheap.  You might need different units if you want to do close range vs. longer range.  Most of the cheap ultrasonic rangers I've seen do about 3cm to 4m.

Here are some cheap modules...  I bought the 5 pin version I think, but haven't done much with it yet since it's pretty low on my priority list.  $5.58 for the 5 pin, $9.10 for the 3 pin.  Both do 3cm to 4m.

http://www.suntekstore.com/goods-14001987-ultrasonic_sensor_distanc...

http://www.suntekstore.com/goods-14002212-3-pin_ultrasonic_sensor_d...

Sorry I can't tell you much about how well they work.  But the quality looks fair to middling and I got what I ordered from this place.

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Permalink Reply by Dave on June 4, 2012 at 7:40am

I tried Alt Hold at about 30 cm yesterday over a flat surface (tennis court).  Each time, the quad was unstable and would slowly rise to ~ 75 cm before stabilising.

I haven't looked at the logs yet.  However, there is a large amount of prop wash coming back off the ground at the low height which could have been upsetting the sonar readings.

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