We are trying to determine if the Sonar has the capability to hold the elevation less then 1 meter. We are attempting to get it to hold things around 30 cm.
When we use the testing routine in the CLI, it appears the sonar starts measuring pretty accurately at around 22 cm. So it would appear that 30 cm would not be too unreasonable.
Any ideas or suggestions?
So what is it in the code that is limiting the distance for the sonar?
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.
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?
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.
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.
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.