MultiWii Yaw problem

[jusjak]

Hi,
I have this problem for more than five months now. I posted this question in rcgroups with no answer. Let me just describe the problem:

In current build, firmware 1.9, frame quad x with 5" propellers, small selfmade indoor frame, AUW 270g, only WMP, when start flying everything looks very good and stable for about 10-15s, than quad starts to, appears like, giving throttle by itself, starts to go yaw left, speeding the move to left yaw. It ends up going left full circle or, it appears, multiple of 90 degrees. This is so anoying that is almost unflyable. If you apply yaw right once it is doing this, quad resists, but if applied long enough it gives up and you can straighten, but after sime time it happens again. Let me just add that sometimes it happens with yaw to the right, but most often to the left.
This is the list what I tried to resolve it:
- changed frame to bigger 7" props
- checked if motors straight and in one plane, checked frame general geometry
- replaced motors, have 6 of one kind, and 4 completely different (Kv 2100, 2200), tried with 2S and 3S batteries
- tried 3 different gyros, 1 original WMP, one clone and one with ITG3205
- tried ESCs Turnigy Plush 6A and 10A, checked programming and throttle range several times
- checked with 3 different controllers, flyduino and 2 selfmade Pro minis
- 5V supply from ESC and selfmade low dropout regulator
- 2 different Rx, same Tx
- tried firmaware versions from 1.7 to 1.9
- MAXTHROTTLE from 1700 to 2000, appears that little bit less problem with around 1850
- tried 3 different gyros, 1 original WMP, one clone and one with ITG3205
- multiple PID values, too many to mention

In MultiWiiConf everything looks OK, debug values at the bottom of the screen stay at 0 for several minutes, with motors on and off, orientation of gyro axis OK, very small noise on gyro values, radio values all from 1000 to 2000, middle 1500 (no yaw drift on radio itself).

Help, I am coming to the point where there is nothing else to try. By the way I ordered KK controller from HobbyKing to try out, it is still on its way.

[Wayne]

Are you using counter rotating props? If not you have to tilt two of the motors a few degrees.

[jusjak]

Yes, I am using counter rotating props. No tilt on motors, all props in the same plane.

[jusjak]

Update:

Received KKMulticontroller from HobbyKing. Installed it on the same frame, everything the same, even propellers.
I am flying inside, same as before.
KKMulticontroller manages to hold yaw, although I can see the tendency to go left on yaw, it manages to hold. From the point of view of roll and pitch stability, Multiwii looks better. Somehow, Multiwii just does not have enough strength to hold the yaw, even with maximum P for yaw.
I like Multiwii much better as it is more stable, behaves better in the air, has more sensor options, GPS. So, I have to dig into the code and find the lines responsible for yaw holding.

Can somebody help with the code and point me in the right direction?

[cardboard]

seeing as you have tested the frame/motors/esc's with 2 different sets of control board you've already seen it isn't a code issue but a hardware issue.

I'm guessing you've rebuilt your quad at least once in your quest to fix the yaw issue and at some point nutted out any other weird hardware glitches.
The main thing that I think causing this issue is at least 1 motor playing up.
it may be....binding, bung bearing, lose prop apt, bad wiring(ether yours or in the wingdings), bung esc, burnt motor or a combo of any or other i didnt list.

Could you try moving the motors/esc around?? use a pen to mark a number on each component and when you move them see if the issue moves as well.
eg: it yaws left atm, if you move the motors and it yaws right afterwards you know at least 1 motor is bad.
if it still yaws left move the esc's as well, if it yaws right afterwards you know at least 1 escis bad.
if you've moved all the esc's and motors around and it hasnt changed at all it may be a frame isssue.
You didn't mention what your frame was made of but if its wood one boom may be cracked and twisting under load.
I have heard of very lightweight frames made of carbon tube flexing in fast flight and handling weird.

Tips to do the above.
use a systematic apraoch to moving the esc's and motrs around eg:move clock/counterclock
troubleshoot motrors and then esc, or esc's then motors, don't move everything at once or you may miss what exact part is at fault.

you could try all above tests with both kk and multwii boards as well, this would eliminate the controller as the culprit.

hope I've given you a few new leads to follow up on, keep us posted on your findings

[jusjak]

Looks like I was not precise enough.

I tried completely different motors (2100 Kv) on Multiwii setup, and it was doing the same. Also, I tried 6 different motors (2200 Kv) and I am pretty sure I rotated them around, although not systematicaly, my mistake. ESCs 6A Plush I did not change, but I remember, from early stages, couple months ago I was using different ESCs, 10A, and the problem was there.

Also, with KKmulticontroller I never saw quad rotating full circle around yaw like with Multiwii. There is a tendency to go left but it manages to hold yaw. I have to add that tendency is maybe there because of, so called, "dirty" air, as these tests are done inside in the room with slanted roof.

So, actually after trying all this, I think it is code issue, or code not being able to hold yaw due to outside cause (like "dirty" air).

I am just surprised that nobody else is experiencing the same. I had a reply from guy with nickname mafO on RCGroups, who had very similar issue, but never heard from him again.

Frame is aluminium U shape 10x10mm, 1mm wall, sandwich inside is carbon square 70x70mm.

[capt]

You might try to re-calibrate your TX centers @1500 in GUI and the end points to 1095-1905. Also as the battery voltage drops it will effect stability, are you using good batteries?
One other thing to try is if you have a different rx or better a tx/rx.. just some ideas.

[jusjak]

You might try to re-calibrate your TX centers @1500 in GUI and the end points to 1095-1905. Also as the battery voltage drops it will effect stability, are you using good batteries?
One other thing to try is if you have a different rx or better a tx/rx.. just some ideas.

Thanks for trying to help capt.
Tx centers are at 1500, end points 1000, 2000. Why to go with 1095, 1905? MultiWii FAQ are stating that end points should be at 1000, 2000. My batteries are good, some are excellent, only couple are bad. But problem is always there. I have only one Tx, it is HK-6X, tried three different Rx, two Coronas and one HK. Wathed the values from Rx in GUI for couple minutes, with motors on and off, there are no unusual glitches, the values walk 2-3 points up down.

Also if there are glitches on i2c line. All debug errors at 0 all the time.

But, the problem is still there...

[Wayne]

Your motors are turning almost three times to fast for a multicopter.
Try sub 1000KV motors. 750KV with 3 cells works best for me.

[jusjak]

Your motors are turning almost three times to fast for a multicopter.
Try sub 1000KV motors. 750KV with 3 cells works best for me.

That may be part of the problem, since my other two bigger quads (with 1050 and 1200 Kv) do not experience this problem. The other thing that MultiWii does not like is motor to motor distance too small. My 5" props are almost touching (6-7mm appart), with m2m at only 190mm.

From the other hand, KK controller does not have this problem with 2200 Kv motors, both 3S and 2S batteries. Also, friend of mine is flying KK with 2900 Kv motors and is flying pretty solid. As I stated before, MultiWii is more solid from other aspects. The reason for this high Kv is to achieve smallest possible overall dimension, for indoor flying, and go with 5"" props. I have seen a lot of other examples on the net, people flying quads with motors in 2000-2500 Kv range and nobody mentiones similar problem.

Oh well, looks like I would have to stick with KK for small quad and practice with it during the winter time and use MultiWii on bigger quads with added bells and whistles when it warms up.