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how to get althold to work properly?

Posted by Johannes on February 15, 2015 at 9:42am

Hi,

i am just new to drones. i made a hexa, using dji e300 esc, dji 2212/920 motors, std props from dji. 

as the fc i use a apm 2.6 (firmware: ArduCopter V3.2.1 (36b405fb))

 Everything kind of worked out of the box as long as i fly in stabilize mode. 

When i swich to althold, the height varies a lot between around 5 to 7 m.

there seem to be 2 Problems: 1. the copter does slow but very big changes in the height. (slowly changing around 3m. the other problem is, that the copter kind of "jumps" around in a smaller scale (around 20cm) and much faster...

What i have done: 

- set the throttle mid from 500 to 525 (according to log)

- checked vibrations (getting max +-2) via log

- lowered the p value for acceleration throttle

- disabled all logging (for cpu load reasons)

I added some screenshots and the logfile, 

i hope someone can help me with this issue?!

Thank you very much!!!

Bildschirmfoto 2015-02-15 um 18.40.26.png

Bildschirmfoto 2015-02-15 um 18.42.04.png

15-02-15_17-15-06.bin

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Replies

  • Johannes February 17, 2015 at 12:31am

    Its possible that i had some trees in the GPS view. But if this was the reason, i am totaly unable to fly between houses?!

    Is this maybe because of a cheap GPS, or is this just normal? What about flying in fog? Any chance to get GPS reception?

    Thanks!

    • Stuart Brookes > Johannes February 17, 2015 at 12:03pm

      Something sounds off with you gps, but even so even with my ublox 8 that uses gps and glonas, it still has its moments.

      Don't expect perfect non fidgeting flight all of the time. Most of the time its good but it does fidget if gps updates weirdly. I have flown near tall trees in a narrow clearing in gps modes, but always ready to switch to stabilise if needed. Flying between houses can have adverse effects in gps modes, just make sure you are good and ready with stab mode and don't rely on GPS. GPS is great, just best not to rely on it.

      What GPS is you have? Looks like a chinese ublox of some sort. Ublox gps are usually ok. 

      • Johannes > Stuart Brookes February 21, 2015 at 9:40am

        Hey, i am getting HDOP Values between 3 and 2 now... I have no idea why it was that bad the one day.

        so i just tried PosHold, and it works pretty good out of the Box. 

        How good is that? Any suggestion how to make it work better?

        https://www.youtube.com/watch?v=1ELc7EN8PeU

        Thanks a lot!!!

        PS.: one more Question: what is the difference between Loiter and PosHold? isnt PosHold just the better Loiter (with ability to manuver?)? Or is Threre a scenario to use Loiter?

        Thanks again,!

        • Stuart Brookes > Johannes February 21, 2015 at 11:42am

          not bad, that does look like a challenging environment for gps...lots of multipath possibilities.

          yeah pos hold is newer and allows maneuvering more inline with stabalise, but with the benefits of holding position when stationary.

          Despite what Cala said I actually prefer poshold to loiter even for smooth slow stuff, seems less prone to gps gitter. Although stabiise is the best, just can be harder work to fly if there is any wind. 

          • Cala > Stuart Brookes February 21, 2015 at 12:20pm

            Yes, I prefer Pos Hold too and stabilize for hard wind but I have the problem, specially the 550  cuad that in one point of the stick the copter goes up and the other descend in stab mode, not very comfortable to fly like that, I try changing mid trottle but I couldn't solve, any idea.

        • Cala > Johannes February 21, 2015 at 9:57am

          Loiter is uses to take slow good videos, try to have HDOP under 2

      • Johannes > Stuart Brookes February 18, 2015 at 4:26am

        Yes, it is a ceap ebay ublox GPS. With this ublox center software i uploaded the config from arducopter.

        I think ill need some further flying to figure out when and where the Problem occures. 

        An other question concearning logs. I figured that the CPU load is at around 95% when logging everything+imu. What happens if the flash runs out of memory? does the copter just drops out of the sky? Or is it a kind of a log stack, where the first gets removed when there is no space left?

        Thanks for all your help!

  • Stuart Brookes February 15, 2015 at 10:10am

    Those vibes aren't brilliant. Try and improve that.

    Is the barometer covered in foam to minimize turbulence and block light to it? The barometer values look kind of noisy too, guess that relates to turbulence protection.

    • Johannes > Stuart Brookes February 15, 2015 at 10:16am

      The Baro is covered with foam. So this should not be the Problem. 

      right now im waiting for this: http://diydrones.com/profiles/blogs/3d-printed-anti-vibration-mount 

      to finish printing.. Ill see what the difference is. 

      I looked at the logfile again. What i do not understand: one can clearly see, that all available sensors show the copter going up and down. (for example GPS, Baro). Why is the copter not simply trying to correct these values? And is there a way to set the priority of GPS or Baro Altitude?

      Thanks a lot!!

      Bildschirmfoto 2015-02-15 um 19.15.03.png

      • Stuart Brookes > Johannes February 15, 2015 at 10:21am

        OK. The baro and gps go up and down, but not by the same amount. Over that time period they should be relatively similar. The software is trying to combine baro, GPS and estimated from the accels.  Bad vibes are notorious at creating bad alt hold control, sort them out before trying to tune it.

        The system is only as good as the inputs.

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