Quad "jumps" with throttle hold steady

[Count]

Hi,

I just finished changing the motors of my Crius SE Quad to Suppo 2212/13 1000kV with 8x4.5 slowfly props. During the first testflight I noticed a behaviour that was not there with the old motors (AX-2210N 1000kV). I apply throttle till the quad lifts off and it flies totally stable in gyro only mode. No uncommanded rolling, pitching, yawing, but it is nearly impossible to hold it at one height. Even without a throttle input, the motor revs keep changing rapidly for small amounts, causing the quad to stutter up and down, like power is lost for a fraction of a second and then recovered on all four motors (the quad stays perfectly level).
I am using HK-HW20A ESCs with SimonK firmware.
I tested with MWC firmware 1.9 and 2.0.
A benchtest without props showed nothing unusual.
A last test I could do, is to mount the motors on my CopterControl Tri and see what happens, but that has to wait till next weekend.
If you have any other ideas what could be causing this, I would be glad.

Count

One thing I forgot to mention: If I try to land and touch down with motors running, the slightest impact causes the throttle to suddenly increase and the quad jumps up again. I had to let it drop for the last centimeters with fully closed throttle, to avoid this.

[KeesvR]

Hi,

I've exactly the same reaction as you describe, I'm almost sure that this is caused by to much vibrations and the faster reaction of the ESC's.

I'm using ITG3205 with LPF 42Hz now it's almost gone, with 98Hz it was really bad.
This problem begun after I've flashed my RC-Timer ESC's.

Now I need to find a better way to isolate the sensors from vibrations, because the RC-Timer motors give a lot of vibrations and I can't get it better.
Best should be some better motors.

[tovrin]

my problem was vibrations from the motor mounts, my symptoms were identical. i noticed mine by watching via the gui with no props on, and saw mad vibrations.

[Count]

Thanks for your replies.
I just bought these motors, because they vibrate much less than the 2210N (the worse problem is, they loosen themselves from the motor mount). With the old motors, only one of four needed no balancing. I tested the new motors and all four feel the same and vibrate less than the balanced old ones.
Perhaps this part of the problem, four similar vibration frequencies have a higher chance to anhilate or amplify each other (in german this is called "Schwebung", "Beat" in english, if wikipedia is correct ), than the different vibrations from the old motors.
Or the collet prop adaptors are the problem. I only tested the motors without them.
Props are balanced, too
I will investigate this further, I only need a new BT dongle for my PC, to see the realtime data.

Count

[Count]

I just did a quick testflight in our livingroom and all problems are gone. My solution was to build a new frame out of 12mm aluminium round tubes instead of the 10mm square ones. The round tubes transfer less vibrations (checked in realtime view) and also weigh less than the square tubes.

Count

[KeesvR]

Thanks, good find.
I've some of these tubes for my next build, so I'm gonna try this.