Help - Undesired pitch when full throttle

Ed_209 · October 2, 2023, 6:45pm

Hello, First copter build. I have been a fixed wing pilot with arduplane for many years but the tuning of copter is challenging me. I have installed a SpeedyBee F405 mini and Matek M8Q-5883 GPS/Compass into my Flywoo Explorer LR 4" quad. I have done successful autotune and POSHOLD works great and locks in.

I have noticed some erratic pitch movements when I punch out when in STAB mode. Also, in ACRO, the quad tends to get a little uneasy. I’m unsure if I have vibration issues or if I need to tweak the notch filter. I am looking at the data but I don’t see anything glaringly obvious. Then again, I am not used to tuning for vibration, filtering and PIDS. Can someone take a look at my log and give me advice? It would be greatly appreciated.

Here are my PIDs as well.

xfacta · October 2, 2023, 7:27pm

It looks like the lack of control happens mostly when the throttle is reduced after a big climb, and of course motor outputs go low, with one or more motors hitting their minimum. At least it’s not oscillations.

Try adjusting these to help that situation.

ATC_THR_MIX_MAN,0.5
MOT_SPIN_MIN,0.20

See if you can get the MOT_SPIN_ARM and MOT_SPIN_MIN a bit lower but still be reliable.

You have extremely low vibrations and noise, so the harmonic notch filter is not doing anything for two reasons:

not needed
slightly misconfigured

So just disable it anyway.
INS_HNTCH_ENABLE,0
You wont see me recommend that change often!

Compass is definitely quite affected by throttle

Luckily you had plenty of yaw in that log so I ran it through Magfit.

Set these updated compass parameters and that should take care of a some of the odd behaviour you see

COMPASS_DIA_X,0.919
COMPASS_DIA_Y,1.080
COMPASS_DIA_Z,0.902
COMPASS_MOTCT,2
COMPASS_MOT_X,3.396
COMPASS_MOT_Y,1.045
COMPASS_MOT_Z,-5.312
COMPASS_ODI_X,0.009
COMPASS_ODI_Y,-0.200
COMPASS_ODI_Z,-0.002
COMPASS_OFS_X,-731
COMPASS_OFS_Y,208
COMPASS_OFS_Z,284
COMPASS_SCALE,1.00

Ed_209 · October 2, 2023, 7:47pm

Wow! Thanks so much. This stuff is so alien to me since with fixed wing I’m not really dealing with vibrations and a compass. It’s interesting you say the lack of control happens when throttle is reduced. I notice it happening when giving it the beans and it pitches forward dramatically but it seems like stabilization saves it from completely flipping out of control. I will have to review some footage to see if I reduced throttle before punching out. I am almost positive I was in a hover and punched out from stable altitude.

I’m shocked that I have low vib and noise. The FC is jammed in there and is actually on a slight angle (I did level cal to ensure it is reading properly)

I assume the compass is affected by throttle because the battery lead is sitting at the rear very close to the compass.

I really appreciate your help. I will try what you said and report back.

xfacta · October 2, 2023, 8:54pm

No I doubt it, most likely that compass calibration should fix a lot. Really I was just saying that I could see the copter loses stabilisation when throttle drops dramatically after a climb.

Check out Air mode too, which is not really a flight mode, but an “enhancement”

Ed_209 · October 2, 2023, 9:12pm

OK so changed everything except MOT_SPIN_ARM and MOT_SPIN_MIN. I will work on that next. I did 2 flights. First one in STAB. Second one in ACRO. When hitting the throttle hard it pitches left. It didn’t feel as violent as before however. In the short flight, STAB felt a lot “tighter”. ACRO still feels sketchy still. I’ve attached the log and accompanying video. I’m going to have a look myself but would greatly appreciate any insight you might have.

Ed_209 · October 2, 2023, 11:41pm

I also just tried airmode, RC5_OPTION=154 for my ARM/DISARM switch. Same result with pitching to the left on heavy throttle.

Ed_209 · October 27, 2023, 11:01pm

I am still trying to refine the tune. Since last time I have flashed Bluejay firmware to the esc and enabled dshot600. Ran autotune and adjusted PIDs manually for the roll to close the DesRoll/Roll. Pitch and Yaw look to be ok. I have eliminated the pitch issue when going full throttle and have a pretty good tune with one exception. It feels like when doing a coordinated yaw/roll right, it is sluggish and gets stuck and kind of turns in bursts. See example in video around 20sec. Yaw/Roll left feels ok.

Overall not as locked-in as it felt when running betaflight. Turned on harmonic notch filtering but I don’t think it’s doing much. I am not sure how to tell what if any interference there might be. I have Magfit running but not sure how to decipher. Any help would be appreciated

xfacta · October 28, 2023, 11:15am

Watching the video, I noticed what looked like a bit of instability during descent or low throttle - correct me if I’m wrong.
I’d like to see how it is with MOT_THST_EXPO,0.45
Motors are sometimes hitting minimum which will affect stability, try: MOT_SPIN_MIN,0.12

I think the wide notch bandwidth is also affecting PID response, try: INS_HNTCH_BW,15
It’s normal to use a narrow bandwidth when using per-motor notches, like 1/4 of the frequency.

Also alter these:

PSC_ACCZ_I,0.4
PSC_ACCZ_P,0.2

They wont have a lot of effect, but will be more correct.
You should also set these too:

ARMING_CHECK,1
BATT_FS_CRT_ACT,1
BATT_FS_LOW_ACT,3

Let’s see the next log and your thoughts on how it is different.

xfacta · October 28, 2023, 11:29am

Also carefully put these compass calibration values in

COMPASS_DIA_X,0.899
COMPASS_DIA_Y,1.020
COMPASS_DIA_Z,0.827
COMPASS_MOTCT,2
COMPASS_MOT_X,0.547
COMPASS_MOT_Y,7.412
COMPASS_MOT_Z,-4.006
COMPASS_ODI_X,0.020
COMPASS_ODI_Y,-0.200
COMPASS_ODI_Z,0.029
COMPASS_OFS_X,-709
COMPASS_OFS_Y,168
COMPASS_OFS_Z,370
COMPASS_SCALE,1.00

Ed_209 · October 30, 2023, 7:24pm

Thank you for your input. I learned a lot over the past weekend with many test flights. I tried your changes and things were terrible. I tried some autotuning for hours but couldn’t get anything decent. I had messed up things so bad, I went back to my last known semi stable config from the 2023-10-27 bin I provided above. I have since rerouted battery leads out the front of the quad and away from the compass as much as possible. I have Magfit installed on my machine so have been doing my own assessments. I am now retrying incremental changes, I think applying all the changes at once was too much.

So right now where I am at is I changed just MOT_THST_EXPO,0.45 and MOT_SPIN_MIN,0.12. I’m confused as to why you suggested those values. Looking at my previous config, MOT_THST_EXPO was set to .52. What would lowering it do? As for MOT_SPIN_MIN, this is a tiny 4" quad with 4S 18650. Naturally, it is heavy with this configuration and needs a little more throttle to start to realize thrust. It was great for cruising with Betaflight. I would think the MOT_SPIN_MIN should be increased slightly to alleviated the instability? Another odd thing I noticed is that the OSD shows throttle around 15-20% however on my sticks I’m hovering around 45-50% throttle. Not sure if that’s an esc or configuration issue but seems off. I’m not sure if the EXPO would take me a little getting used to but it felt twitchy compared to the previous flight. I almost lost it on takeoff!

Here are the respective bins and videos. Again, any input you could provide. I think I am getting serious compass interference from the motors or battery wires still. My thought is that I have to get rid of compass issues before going forward with any more changes if I really want to dial-in the tune. Not sure what else I can do. I read about compass motor calibration but I also saw that magfit can be done instead.

Pretty good stability, used my own magfit after test flight.

Changed MOT_THST_EXPO,0.45 & MOT_SPIN_MIN,0.12. Very twitchy. Could be me needing to get used to it.