Octo starts yawing when adding weight, wich PID to adjust?

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Octo starts yawing when adding weight, wich PID to adjust?

Postby Lindbaergh » Sat Jul 06, 2013 11:06 pm

Hi im still working on my octo for heavy cameras (>2kg), when i fly without a camera everything is ok and working (RTH,ALT/POSHOLD WAYPOINTS etc.). But when i add the weight of the camera (around 2kg) the octo starts yawing cw wise, and is ignoring my yaw stick input (i include a log of that).
Im not sure wich PID are to change to compensate that, maybe someone can point me to a direction in the PID settings?

thanks in advandce Michael
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Re: Octo starts yawing when adding weight, wich PID to adjus

Postby Max » Sat Jul 06, 2013 11:59 pm

Hi Michael,

There's no log attached... But regardless, before you add the camera weight, what does your MOT_YAW output look like? Is the average around zero?

I don't know why adding weight would cause a yaw problem like that, by itself. Most likely it is compounding an already-existing problem (or maybe the CoG gets thrown way off). What mix are you using? Is 2Kg a lot in relation to the AUW w/out camera? Are you changing props or anything else compensate for the difference in weight? Many questions... :)

-Max
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Re: Octo starts yawing when adding weight, wich PID to adjus

Postby Lindbaergh » Sun Jul 07, 2013 10:26 am

Hi Max

Sorry i messed up the logfile upload, here it is:
http://www.flugbaerchen.de/lnkimg/aq6/006-AQL-.zip is with extra weight.
http://www.flugbaerchen.de/lnkimg/aq6/007-AQL-.zip is without extra weight.

The Octo is around 4-5kg without a cam, ready to take off. I use esc32 and tiger mn3510/700 motors with 13x4 xoar props on 4s. The motormix is taken from Larry:
Motor thro___ pitch___ roll __yaw
1______100____70____0__-100
2______100____50___-50___100
3______100_____0___-70__-100
4______100___-50___-50___100
5______100___-70____0___-100
6______100___-50___50___100
7______100_____0___70__-100
8______100____50___50___100

In the past i use a canon 600D (~1kg) for all tests and pid adjustments. Because i also want to use more heavy cameras in the future, i put 2kg cam dummy (2 bags of rice ducttaped together to a nice package :) ) to the gimbal. When i try to lift off the octo starts spinning cw wise, so i have to bring it down immediately. I tried this 3 times but no chance to bring it up. I then removed the extra weight it flies fine again. I will use the fine weather today to do some additional testing with different weights and will try the build in mixing table of QGC.

Michael
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Re: Octo starts yawing when adding weight, wich PID to adjus

Postby LPR » Sun Jul 07, 2013 2:31 pm

Michael

I just changed yesterday to the recommend motor mix in the QGC and my octo is flying well with it.
Max's suggestion to look at the LOG_MOT YAW output is a very good one. You more then likely have the yaw off center because of the tilt of the motors. A small tilt can make a big difference then your try to haul some weight.

Larry
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Re: Octo starts yawing when adding weight, wich PID to adjus

Postby Max » Sun Jul 07, 2013 9:33 pm

Yes, your MOT_YAW is way off... W/out the weight it can just manage to keep control of yaw (except in a couple spots), but with the extra weight it can't (except in a couple spots :) ). There is definitely an imbalance somewhere, or motor(s) aren't leveled properly, as Larry suggests. With the extra weight (6.5 vs. 4.5Kg AUW) you're getting close to the (calculated) capacity of those motors/props and asking them to work ~20% harder during hover.

Also do try the recommended mix from QGC first and only adjust that if it becomes necessary (it shouldn't, especially with the extra weight you'll want all the power available).

-Max
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Re: Octo starts yawing when adding weight, wich PID to adjus

Postby Lindbaergh » Mon Jul 08, 2013 10:34 am

Hi Larry and Max

I will change the motor mix, to the predefined GQC one. I also will check for Motor miss alignment again, but i'm pretty sure that the motors are mounted well (looking at it is part of my preflight check list).
The LOG_MOT YAW gives me a hard time, when i look through the archives (the last 8 month) of logfiles it is more or less all the time under zero. But there are big changes in the setup, i used mt-4006/rct4215/mn3510 motors and esc32/simonk nfet controller in different combinations. so maybe there is something wrong with my frame, it is the fcp-hl from flyduino. I think i will do a complete reassemble of the airframe to see if something is wrong. Also i will set the copter to a strict diet, i think that is always a good idea :).

thank you for the tips, i hope to see you at the maker faire next month. Michael
Attachments
LOG_MOT YAW-04.png
LOG_MOT YAW-03.png
LOG_MOT YAW-02.png
LOG_MOT YAW-01.png
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Re: Octo starts yawing when adding weight, wich PID to adjus

Postby Lindbaergh » Tue Jul 09, 2013 10:06 pm

Hi again.
Today i changed the mixing table to QGC default. The result is a copter that can carry some more weight (not the full 2kg+ but around 1.5kg, enough for me). It needs some pid tuning now, in althold it moves up and down. There is still a problem with mot_log_yaw, the log looks a lot better then before but not good at all compared to log files of other users. The CoG is nearly perfect, only minimal adjustments needed. The frame is a bit tricky, and needs some serious adjustment/fixication, there is still work to do.
Is there anything else that i can check to fix this out of bounds mot_yaw issue?

Michael

logfile of the day :) : http://www.flugbaerchen.de/lnkimg/aq6/017-AQL.zip
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Re: Octo starts yawing when adding weight, wich PID to adjus

Postby chschmid » Tue Jul 09, 2013 10:17 pm

Hi Michael

Only very small disadjustments of one of the motoraxises can have that effect. There could also be a motor with different KV or a prop with slightly different size or pitch. All arms should have the same length and be on the same plane. Well, that's about it what comes to my mind right now.

You said, that you where using different ESC's and always have the same effect. Maybe it would be good to verify that your ESC32 have the same settings anyway.

Cheers
Christof
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Re: Octo starts yawing when adding weight, wich PID to adjus

Postby Lindbaergh » Thu Jul 11, 2013 5:16 pm

So yesterday i fixed some flaws on my frame, to bring log_mot_yaw to normal. Today i have some testflights with different weights and i think the log looks pretty well now http://www.flugbaerchen.de/lnkimg/aq6/019-AQL.zip .

When i wrote that i use different parts, i meant whenever i change something, i change all parts and do recalibration etc. if necessary. So i never mix different props, esc or motors.
I start using mt-4006/esc32, but i ran into random disarms of esc32 while flying (i suspected the combo of motor and esc, and found out much later in time that i have placed the esc32 to close to each other, so they causing interference).
Then i changed to rct 4215/simonk esc, that combo work but the motors have not enough power and the bearings are horrible. so overall performance was to low for my needs.
The next combo was mn3510-700/esc32, the same esc32 as above (with new calibration) and they still making trouble with random disarm. Then i changed the placement under the bottom centerplate, and they work fine since that change. This is the set up i use in the moment and be well satisfied. The only thing left to do on this is to change the pid for althold mode because after changing the mixing table from Larry's one to default, althold wont work very well anymore.

so thanks again everybody for helping me out.
Last edited by Lindbaergh on Fri Jul 12, 2013 8:34 am, edited 1 time in total.
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Re: Octo starts yawing when adding weight, wich PID to adjus

Postby chschmid » Thu Jul 11, 2013 10:48 pm

Good to hear that you solved your problems.

Cheers
Christof
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