[vgwit]

Hello guys.

Have upgraded from CC3D to Revolution mini. Have set default settings for all related settings. Take off in Attituded (Rattitude) mode, everithing looks fine then switch to AltVario, slightly touch throttle and my quad stops props and falls down. Next time go first in AltHold - looks fine, then switch to AltVario. But even don't touch throttle - it stops props and falls.

Have set Max Vertical Velocity to 1. AtlVario works perfect. Then change to 2,3,4, - works good also. Then set it to 5 and quad also flies good! Unpredictable behaviour.

Stabilization algorithm is Basic. What it could be? Here are FPV video of crashes:

https://drive.google.com/open?id=1N1ZjWwpeP2gOiAwwKkBRTq4gKpVyjnGP
https://drive.google.com/open?id=10iGDumksDvlK2V3QEDj9-5DCv339lInW

Thanks.

[vgwit]

Added my config.

[TheOtherCliff]

AltVario controls vertical the speed, not the power, so full power may be 3 meters per second up, and almost zero power is only 3 meters per second down (I forget the default).  This is much slower than Manual thrust mode.

But (as a safety feature), if you move the throttle stick all the way down, the motors stop and it falls.  So at 5% stick, it is coming down at a reasonable rate, and a tiny bit lower throttle and the motors stop.

And if your Input Throttle Neutral is set wrong, the motors may stop at a much higher throttle stick position.  Typically, the Input->Throttle->Neutral should only be about 40 above Minimum.

(Edit:  I didn't look at your config.)

[vgwit]

Thank you Cliff,

Now I think my problem is not related to Alt Hold or Vario because I couple of times saw it in Altitude and Rate modes. It looks like something is wrong with channel for 4-th (SouthWest) motor. I.e either motor itself or its ESC or PWM signal from FC. The problem has appeared after transition to Revo so FC is most probable as a culprit. But what specificaly wrong with FC - here is a question.

By the way, may logging in GCS or Android version help in this situation?

And another question. I know that gyros are calibrated at arming. A quad gets armed after this calibration or right before it? If after then how long does calibration take?

Thanks.

[TheOtherCliff]

Logging can definitely help diagnose.  You might need to play with enabling some additional logging.

It usually requires playing back the log (sometimes at slow speed) several times to see what went wrong.

Don't rule out a failsafe.  Are you using FC failsafe or RC failsafe?

I had this problem.  It turned out that it was a bad cable and one of my PWM inputs would disconnect and the FC would failsafe.

[vgwit]

It is not failsafe. I noticed that during crash 4-th motor exibits a problem with rotation first while other 3 still rotate prperly some time.

I switched on 4-th motor in Output screen of GCS and jerked rather hard cables from FC to ESC and the motor. No problems.

[TheOtherCliff]

I think I have seen that if a motor or ESC goes out, that the others are very quickly reduced by the FC stabilization and it doesn't look like just one motor failure.

Also, I have seen ESC/motor that works fine if a human is manually moving the throttle position, but when the FC is controlling the motor and stabilization or baro altitude makes a sudden, large jump, that the ESC/motor stutters.  In my case, the motors would not start unless I held the quad level when I started them.  The motor that stuttered was the lowest one and thus was asked to jump to the highest thrust of the four.  I just had to try again, with a tilt that made which ever motor was stuttering a little higher.  The problem was permanently fixed when I upgraded the BLHeli/SimonK (I forget which) to the latest version.

Is your battery old?  Do you have a LiPo alarm on it?  There is a small chance that sudden motor surge causes brown out and reset.  Is it still armed after the crash (I assume you don't use an arming switch)?  If it isn't armed, then it reset.

[vgwit]

After crashes quad keeps arming state.

Here is a short fpv video of one of last flights.

https://drive.google.com/open?id=1enBtfQQuWGOa3WcY-432ss3NKdBd5aJM

 It is Rattitude mode. I armed it on the ground, waited some time and lifted it up by hand near level. Then increased throttle. At about 25% quad suddenly jerked left and backwards. This moment I noticed that 4-th motor stutters. I zeroed throttle, waited some time time and then rose throttle again and quad this time started flying. What was it?

[vgwit]

Hi,

I think I've made a step to solve the problem. Looked at signal from FC to ESC on channel for motor 4 and found a kind of strange signal. It looks like this wire (trace on PCB) touches another wire. Have found how to assign ESC/Motor 4 to output channel 6. Will test this config.

Attach a picture of the signal.

[TheOtherCliff]

Yes.  Go to Vehicle page, Motor Output Channels section and change that motor (SW?) to a different output (Save).

Then go to Output page and make sure that the bank for that channel has the same settings as the other banks in use (Save).

Of course move the connector to the new output. 

That is a strange looking waveform.  You didn't set that output for some other function did you?

What oscilloscope are you using?  I am thinking of getting a USB oscilloscope.

[vgwit]

Have moved motor 4 to output channel 6 but waveform look the same as on channel 4. Don't understand that. Signals on channels 1-3 are clean, without those hints on mixing signals.

Yes, I'm using USB oscill.

[TheOtherCliff]

Try moving the output to a different number, so that is is actually on a different Output page "bank".

[vgwit]

Hi,

Strange waveform on channel 4 - it was my fault. Now signals on all channels are clean. I've found that probably all ESCs/motors are good and something is wrong with stabilization.
Here is a short video of motors stattering on start:

https://drive.google.com/open?id=1MsYmcdMeiLsYJyXoMHctxZSSKrPptW3m

LEDs became lit right after quad get armed. Stattering may be observed on different ESC/motors and not always on which is lowest.

More often motors start properly. But having some flight crashes I suspect they could happen because of this stabilization problem.

What I can not understand is why on my previous CC3D FC this problem was absent completely. All hardware is the same. ESCs are DYS 20A BlHeli.

[TheOtherCliff]

It seems that motors go fairly high as soon as you start them.  Make sure your Input page Throttle Neutral is about 40 above Throttle Minimum (typical setup that has throttle going from 1000 to 2000 some transmitter protocols have different ranges).  Also all your Output page motor Neutrals should be about 80 above Minimum (typical setup that has motors going from 1000 to 1900/2000; some ESC protocols have different ranges).

I had some ESCs that came with old firmware and did not like to start quickly, but would start slowly, so doing Output page Test Outputs would work fine, but some motors would not start when about to take off.  I was in Attitude mode and it was always the lower motors (very slightly lower because of ground unlevel) that would not start.  That was because they were being asked to start at a higher throttle then the "higher up the hill" motors.  Once the motors were started, I didn't have any problems.  Temporary solution was to very slightly tilt the quad to elevate the motors that would not start and retry.

A test to try:  Using Attitude mode, set it unlevel by say 10 degrees and see if the lower motors consistently have a harder time starting.  You can then just manually hold the quad very slightly tilted with the hard starting motors higher.  You can also switch to using Rate mode for a test.  Rate mode should not have this problem.

[vgwit]

Thank you Cliff.

In video I've posted above I intentinally started motors more quickly than I usually do. Here is a couple more with slow start.

https://drive.google.com/open?id=1tI7UQfqRxUXeIl4GuU0JtVsZG-BlI3JD
https://drive.google.com/open?id=1AyIMl4nwq1-uyl5AwAawEtUAIFpwlO-v

My neutrals are 1028 and was like this on CC3D. Will try to increase them.
And an important note. I saw the problem in Rate mode also but did not recorded a video. Will do it today.