AQ drops in manual mode [solved]

[r0sewhite]

After several well-running AQ copters I now have an AQ with a strange behaviour. The copter suddenly drops in manual mode and forces me to catch it with high throttle values. As you can see from the logfile, throttle factor isn't yet perfect but this shouldn't affect hovering in manual mode.

Vibrations are not the very lowest but not too boad for such big props. I have had copters with much more vibrations and that only led to high mot_pitch/mot_roll outputs and in very bad cases the copter was shaking a little. This symptom of sudden dropping is new to me.

Motors are Tiger MN3510-15 with Tiger 15x5" CF props. Batteries are 2x APC 4S 4500mAh. AUW of the copter is 3.250g.

Logfile:

[bluuu]

I think it's something mechanical (if any) or windy day and probably (unknown words, I will use the description) air flow after prop bounced of field and do "airbag" on low alt.
You have big props and X8, air speed is strong.

[chschmid]

Your UKF_ALT looks strange in the log. It is not following the GPS_ALT. How did you cover your baro?
At every "drop" your mots "go wild". I see also a heavy clipping in MOT_YAW.
Applying power seems to generate a heavy imbalance. MOT_PiTCH and MOT_ROLL are going wild, ROLL is worse.
Applying power generates high vibes.

My best guess would be
Check if you have the motormix right. The yaw clipping should not happen.
Check the baro cover.
Your copter has to much vibs.

What exacly causes the drop is hard to tell. Maybe a combination of the above.
Hope that helps

Cheers
Christof

[bluuu]

compare mot_throttle with radio_channel 0 - motors reacting with stick command, nothing strange

[r0sewhite]

Christof, about which yaw clipping do you talk? mot_yaw is not even +100/-100 in this log.


Anyway, my problem is solved. I should have noticed it sooner: There is nothing wrong in the log except the GPS signal. With nothing wrong I mean that there is not even a strange output drop on any motor that would explain this behaviour. This means that the copter dropped though the PWM outputs remained at the same level.

The solution is as suprising as simple: These props can't handle low speed and stalled. I added 1kg payload today and the copter flew perfectly smooth.

[chschmid]

[r0sewhite]

Christof, there is no clipping at all if you zoom in.

Stalling is mostly known from planes when they fly too slow. Below a minimum speed the wings stall and lose their lift. This jojo- or rubberband-effect is also known from overpowered (3D) helicopters. If there is not enough pitch, the blades don't give any lift anymore. In my case I just had to add some weight or use smaller props. The tiger 15x5" props obviously stall below 500g load per prop.

[chschmid]

[Max]

E-calc shows hover at 20% with that motor/prop config and your original weight. Maybe 1200 rpm, if that? Even with an extra kilo it's only 27% @ 4A. Wow... gotta check out those motors. Are they smooth running?

-Max

[r0sewhite]

Hi Max,

jep, efficiency is pretty good and almost 16.000g total thrust is a lot

The props are amazingly well balanced, not even statically but also dynamically. None of my props has a range with stronger vibs. The only thing that diappoints me is the stalling problem. I hoped to have a high quality option to Smartdrones props which are also highly efficient but not very well balanced. I used the 15.7" Smartprops with much lower speed on even lighter copters without any problems.

Motors are runnings smooth and I was able to run R2V calibrations up to 20A. CL calibration failed but I'm going on to try it. Only little disappointment with these motors are the aluminum washers between lower bearing and c-clip. Like on other Tiger motors they are too soft/weak which leads to a little play after a few flights. I will replace them with harder washers. Maybe copper would be a good choice.


EDIT: Just read that you will come to Hannover in August. I will be there with our cam lifters so you can see the X8 with the Tiger motors and props.