I've been struggling trying to get reliable altitude data for my quad.  Whenever I try altitude hold, it'll continually rise or fall, but not hold any sort of steady altitude.  In testing I've let it get to the point where it landed and where it rose over 50ft after engaging altitude hold.  Here's my config:

 

Standard 3DR Quad kit with electronics (APM1 w/oilpan)

MB1200 XL Sonar with power supply filter installed per wiki

3DR Sonar Mount

900MHz Telemetry Kit

Turnigy 9X TX/RX

5000mAh LiPo

 

I'm using the BEC from one of the ESCs for my APM power.  My sonar values seem very accurate when I move the quad around myself without the motors running.  When the motors are running the sonar data becomes very erratic. 

 

Here's a pic of the tuning graph when I'm moving the quad up and back down without the motors running:

nomotors.jpg

 

Here's a pic of the same graph when the quad lifts itself to the same altitude:

motors.jpg

 

It seems like the value is almost stuck around 0.4 with the motors running.  The spikes you see are the correct alitude, but most of the time it's stuck at 0.4.

 

Any ideas on how to get alt hold working?  I have a pretty stock quad, so I'm hoping someone else has already figured a way around this problem.

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Long story short, I went from this first graph, which has shielding, filtering and heat, to the second graph:

By making this fugly mount to isolate vibes:

R_Lefebvre,

I just  mounted a sonar on my little quad.  I want it to hold the elevation at 1 foot or so.  Is this possible and if so.... can you help?

Thanks,

Rick

By looking at the APM Planner's Flight Data Tuning graph, look like it wants to follow the targetalt in 1m increment.  So, the lowest would be 3 feet.

Hmm....when I did the CLI sonar test, it appears to start measuring pretty accurately around 22 cm.  And in fact, today I was flying it indoors and I did seem to notice a difference when the sonar was engaged at just under a foot off the ground?  Was I imagining things?  :)

Yea, the sonar is very accurate for down to 20cm, which is the alt in the Tuning graph.  My heli also able to hover at 1 foot off the ground at times as well.  But when it didn't work, I looked at the Tuning graph and it tried to get the heli to follow the targetalt.  And the targetalt seems to only increment in 1m.

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