Yaw change also changes elevation

Recently I built a hexacopter and have flown it a total of three times now. Yesterday was the first time I tried the yaw while in flight. When changing the yaw it dramatically changes the elevation, like 30+ feet of increased elevation for a 90 degree change in yaw. This is very scary to me. Where should I look to resolve this so a change in yaw doesn't affect the elevation?

I'm using the Turnigy Talon Hexacopter frame, NTM 35-36a 910 Kv motors, and APC 12x3.8 SF props. The Arducopter firmware is version is 2.7.1 with everything at the defaults except for the roll 'P' parameter for stabilize mode which is tuned to a lower value from the default (0.08) as the roll was very aggressive with the default. Thanks for your help!

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  •  I am planning to setup a hexa lie yours but Everyone says Turnigy Talon Hexa is small for 12" props. It fits slightly to this frame i think only 5-6 mm gap between props right? 

    What is the effects of small gaps between props? Efficiency? or something like that?

    I need 12" props because of my high trush needs. 

    Any commends appreciated

  • Developer

    By the way, we have two theories as to what causes this:

       1. that the motors speed up faster than they slow down.  So when you yaw, two engines speed up, two slow down..because the ones speeding up get their faster, this adds some momentary increased thrust.

       2. that the pwm->thrust of the motors is not linear (we know this).  if we add "x" to some motors and "-x" to the others..because of the non-linearity (aka thrust or throttle curve) this doesn't even out and we end up with an overall increase in thrust.

    It might be good if you logged your motor output by going into the cli and typing "logs", "enable motors".  when you plot the motors you may find that even in a stable hover that 3 of the motors are much higher than the other three.  This is an indication that some of the motors are not on straight and are leading to a general yaw..the PID loops can hide a lot of this but when i had this problem, it contributed to a large rate climb when i yawed the copter similar to what you're seeing.

  • Developer

    What is your throttle level when you hover? It's odd since this version had a piece of code called a yaw differential which was explicitly there to prevent this. We found it had other negative side effects to stability so it was removed and a different approach was used.

    Try and lower your Yaw_rate_P.

    Jason

  • I would strongly suggest you install 2.7.3 instead of 2.7.1

    There are many changes and fixes in the new release.

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