Discussions

AC3.2.1 APM 2.5 Throttle pulsates in Loiter

Posted by Rolf Inge Sivertsen on February 24, 2015 at 1:47am

Hi.

I have a problem after updating AC to 3.2.1 from 3.1.5.

When in Loiter, the the speed of the motors rev up and down/pulsate quite rapidly. This was working fine when I was using previous versions of arducopter.

I have downloaded the logs, and have looked into accX, accY and accZ. These seems to be inside the range specified in the wiki at arducopter. (Log_vibrations.bin)

Please have a look at the Log.bin, and note the difference between ThrIn and ThrOut when I'm in Loiter mode.

Anyone having any idea what the problem may be?

Log.bin

Log_Vibration.bin

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Replies

- - - Cala > Raph April 10, 2015 at 4:08pm
      
      Raph: in your last log vibrations levels looks bad, specially acc Z affects baro and try to climb
      
      but your acc x and Y aren't good too and made the cuad to oscilate and your x and y looks different, I hope that you can move your controller with your hand side to side but not forward backward correct?
      
      Did you have a crash?
      
      What you can do:
      
      Check your motor props balance
      
      Try fixing your controller directly with doble sided tape
      
      Control your motor mounts, arms etc.
      
      Looks here for more ideas http://diydrones.com/forum/topics/vibration-isolation-and-dampening...
Markus Horeld April 8, 2015 at 10:38am

A question regarding Throttle Accel P&I tuning: The wiki says:

"These values should never be increased but for very powerful copters you may get better response by reducing both by 50% (i.e P to 0.5, I to 1.0)."

In my case (powerful 310mm Quad) these values are yet at the bottom of the "Climb Sensitivity" slider (P=0.5/I=1.0). But as I have the known throttle pulsing in AltHold mode and the Quad loses hight very significantly during pitch and roll commands I am wondering if I should rise these values despite of the wiki instructions. I am a little bit worried to try it...
- Andrew Harvey > Markus Horeld April 8, 2015 at 11:49am
  
  This is a very good question and I am curious myself. If I increase these I don't want a flyaway!
Tim V April 7, 2015 at 10:03am

Experiencing similar issues after upgrading to 3.2.1,

First noticed on autonomous mission there would be a pause on flight legs where the discrepancy in altitude was outside permissible range, flight would pause(hover), then continue on.

Next day, took the rig out to do an autotune, which then created a pulsing action in AltHold and in Loiter, and flight is Stabilize was ok. Did multiple tweaks to PID's to smooth out the pulsing to no avail.

The Z axis vibration values appeared to be high, thus removed the foam shipped with the Pixhawk and used the Kyosho Z8006 gel. The vibration values did decrease some, and still getting the pulsing action in AltHold and Loiter.

May roll back to 3.1.5 if not able to remove the pulsing.

Cheers!
- Andrew Harvey > Tim V April 8, 2015 at 4:02am
  
  I tried Kyosho Zeal Gel but it didn't do much to reduce vibrations in my quadcopter.
  
  I recommend the mounts from readymade3d.com. These use rubber dampening balls. My Z axis vibrations were reduced from 1.5g (!) to 0.1g. I was pretty amazed! See my thread on rcgroups...
Andreas Lachan April 6, 2015 at 3:46pm

For the record I got some time today trying to tune with 3.2.1 with not much luck. I guess I'm not experienced enough to make a tune from scratch without more input than the tuning guides provide. Stanges part is that I managed to get the pulsing, really pulsing not oscillation, with some tuning values. I gave up this time, rolled back to 3.1.5 and it flew perfectly well in loiter with barely any parameter touched. I will try later on with 3.2.1 with settings from 3.1.5.
- Henny V > Andreas Lachan April 6, 2015 at 3:58pm
  
  Have attached a Youtube video link for your info
  
  https://www.youtube.com/watch?v=EQ3sGc2wJgQ
  - Andreas Lachan > Henny V April 7, 2015 at 9:24am
    
    Thanks Henny that is a quite instructive tuning vid but since the problem is that I cannot get Alt hold working properly autotune is out of the question. It is probably more related to the Throttle Accel. values acc. to some suggestions and there I havent seen a guide.
Andrew Harvey April 5, 2015 at 6:28pm

I am experiencing the same problems with my HKPilot Mega 2.7 and AC3.2.1. Haven't yet tried downgrading to 3.1.5 but that is on the cards.

Interesting, the throttle pulsing problem only manifested after adding some weight which pushed my throttle mid to 650. Wind also seems to exacerbate the problem. I have made sure to cover the baro with foam and black tape, although my baro still seems to fluctuate quite a lot.
- Andrew Harvey > Andrew Harvey April 6, 2015 at 2:33am
  
  You are absolutely right - I completely underestimated how involved this was! However I have learnt an incredible amount over the last few months. So far it has been a very long process of elimination.
  
  I am curious as to the relation between the ATC parameters and the more conventional PID values, which I have been focusing on.