Uncontrolled behaviour after take-off (DIMU with Tare)

[rput]

Hi all,

In testing the DIMU I ran into what seems like the same problem several times, except now I finally was able to log it (first time forgot SD card, 2nd time SD card didn't work).

First time: Had been flying a bit in manual, position hold, RTH, and waypoint modes. Then changed batteries and sent a mission with an autonomous take-off. Throttle to 30% in manual, then switch to mission mode and throttle to 50%. The copter starts to rise but at about 10m it suddenly starts a steep bank to the right and increases throttle audibly and loses control. Before I have time to go to manual it makes a semi-circle and crashes into a building (no worries, empty warehouse). Had to replace a Recom and some props etc.

Second time: Tried a take-off in PH. Throttle to 30% or so in manual, then PH on and throttle quickly to 85-90%. Copter takes off and rises but has some slight drift. Then it seems to lose its position and drift faster and then steep pitch and goes off in forward direction very fast. I switch back to manual and land without issues. Without turning the copter off I take off again in manual and switch to PH. Now there seems to be no problem, position is quite stable and I fly around for a while. Unfortunately the SD card logging was not working this time.

Third time (10-15 minutes after 2nd time): I got the SD card logging again and replaced battery. I try to reproduce the issue with success. I take off in PH like before and it rises with some slight drifting when suddenly the motors seem to go full power and the copter rises fast and tilts forward. I switch back to manual and recover. After reboot I fly with manual take-off and PH works like normal.

I reviewed the log (attached) and my tentative conclusion is an issue with the GPS. The GPS altitude suddenly drops right before the motor throttle goes through the roof.

So several questions:
1. Do you agree that this is a GPS glitch or is there something else happening?
2. Why does the UKF_PRES_ALT also show the same dip at 7.2secs while ADC_PRESSURE1 is showing normal behaviour?
3. Any suggestions on what can be done to prevent this?
4. Are the vibrations too high?

Here some additional info:
- AQ 6.1 with R372-DIMU 1.1 FW
- Quad-X setup with ESC32 and Tiger Motor U3
- AQ GPS and ground plane
- Statically balanced TM 12" props
- Total weight around 2.5kgs

Sorry for the long story, but this is puzzling me. Hope that someone can help me.

Cheers,
Richard

[skew]

the way I do takeoff missions
arm leave throttle at 0
flip to PH for .5-1 secs
then flip to mission and raise throttle to 50%

also make sure you plug up the battery where you are talking off it seems to not take off and fly right if you plug in the batt and carry the AQ to the first take off spot.

[s_sergiu]

Hi,

You have too much vibration . AccX is reading almost +- 5G, AccY +-2G and AccZ +-2G. When copter is suddenly increasing throttle while in PH, you have too much noise in Z accelerometer. You should have max. +- 0.5G. Couple of weeks ago I bought T-Motor 15" CF props with MN4014-11 (bought many times before this combination from same supplier) and made one Quad (30mm CF arms) with DIMU. At beginning I did not understood why with my usual PID values, Quad is behaving so bad. Then in manual flight, in hovering, I seen from SD card logs more than +-2G vibrations. I found that all props from CW side were unbalanced (including spares). You must balance each propeller then run each motor separate while logging. For each motor should not go more than +-0.2G in all 3 accels. axes.
Regards,
Sergiu

[Jdmagoo]

[rput]

Thanks guys, I can take another look to see if I can reduce vibration further.

The GPS issue seem unconnected from vibration however. Any thoughts on this?

Here are some pictures for easier analysis:

graph_GPS_HEIGHT.jpg (21.06 KiB) Viewed 14096 times

graph_MOT_THROTTLE.jpg (23.92 KiB) Viewed 14096 times

In the following images you can see that UKF_PRESS_ALT is following the GPS instead of the pressure sensor:

graph_UKF_PRES_ALT.jpg (22.33 KiB) Viewed 14096 times

graph_ADC_PRESSURE1.jpg (21.43 KiB) Viewed 14096 times

[rput]

Does anyone have any feedback on the GPS issue?

Is anyone performing auto take-off without issues?

[skew]

Mine has been flying full missions better than ever. Auto take off has never been an issue with mine it was always the Return to Launch and Landing that didn't work quite right. But I have a fully working AQ now.

[rput]

Hi all,

I had what seems like the same issue again. Flying nicely, put in PH, then I move higher and stop....start to move down....and suddenly the copter seems like it lost power. Motors throttle down completely and falls like a leaf. I quickly switch to manual and it recovers immediately.

After reviewing the logs, there is a clear jump in the GPS altitude which causes the problem.

Normalized values: Light blue = Pressure, Dark Blue = GPS Alt, Yellow = Motor Throttle

Notice the GPS height goes up as I throttle down. The pressure response is normal.

Is nobody else experiencing this with the DIMU?

[LPR]

I've had problems with GPS when the GPS cable is damaged. If the shield on the cable is damaged you will have trouble. Look closely where the cable in soldered to the antenna for damage to the shielding.

If your cable is bad here's a video to help with repairing it.

viewtopic.php?f=33&t=1234

Larry

[chschmid]

Could you post a detail pic of your GPS antenna and wiring.
Cheers

Christof