Another Alt Hold tuning question

I have found my APM 2.5 Hexa copter really solid to fly but I am having trouble getting alt-hold to behave the way I want.

I have a older mikrokopter quad with entirely stock parameters that has unbelievable alt hold, I mean I can hit alt-hold at full throttle and the quad just smoothly halts and stays put.  I have no idea how they implemented their control scheme but it must not care about the throttle position when you engage the mode.

In APM2.5 hexa I can get the tuning to work across a wide range of values as long as I am close to a hover when I engage alt-hold.  I found I got significant unwanted behaviour whenever I tried to tune the throttle D term to anything but D=0.  I found D=.001 to .01 worked sometimes but then I would get a random sinking of the hexa right down to the ground.  All these issues were related to engaging alt-hold.  Once stabilized, almost any settings worked well.  If I had lower P values I found the machine started twitching as I tried to raise the altitude.

I have read the wiki several times but there is not much other advice in other threads. 

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  • Based on the other thread, I should add to mine that I have no sonar sensor, My APM 2.5 is in the APM 2.0 little plastic case, there is black tape immediately above the baro sensor to block light, and there is a small cotton swab sitting on the sensor to prevent any gusts from affecting it.

  • I'm interested in this also. There is another post that is along this topic. I think we share the same problem but first I like to understand how it works.


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