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PID tuning a 500 mm Quad
#1
I have a quad with the following specifications:

Flight Controller BeeRotor F3
BetaFlight 3.0 
betaflight_3.0.0_SPRACINGF3
Frame Hobby King X550 
'Wheelbase' 500 mm
Emax MT2215 935 KV motors
ESC SimonK 30A
Props Gemfan 8X4.5  

I desperately need some help to get the quad to fly properly. I have read countless articles on PID tuning and so far over several months I have completed 60 test flights without getting satisfactory outcomes. This is my fifth quad build so I can assure you that the build is good. I have followed the tuning procedure outlined in:
https://oscarliang.com/quadcopter-pid-explained-tuning/ 
but am finding no constant outcomes. At present when in Air Mode it flies like a drunken sailor, it is just tolerable when flying in Angle mode. One thing I am wondering about is loop time, it shows as 500 whereas say a year ago loop times were around 2500 and 3000, is this system too fast for my needs?

I hope I can get some help thus

Thanks in advance
Hank Deucker
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#2
Hm... I don't know the escs resp. SimonK firmware... How good are they at active braking?

Short looptimes shouldn't be a problem.

Does it feel like it's unstable around center stick? You might try to increase dterm transition slider, i found it has big impact on general PID behaviour. Default is very low.

Also a log file could help, preferably without angle mode.
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#3
(02-Mar-2017, 11:58 AM)fftunes Wrote: Hm... I don't know the escs resp. SimonK firmware... How good are they at active braking?

Short looptimes shouldn't be a problem.

Does it feel like it's unstable around center stick? You might try to increase dterm transition slider, i found it has big impact on general PID behaviour. Default is very low.

Also a log file could help, preferably without angle mode.
Thanks for the reply, I need some more info for me to reply sensibly.
I don't know the term "dterm transition slider", all I know about is the D in the PID
 By log file do you mean a Balckbox file, that I can do but it will be small as I usually end up crashing within 20-30 seconds in AirMode.

Thank you for taking the trouble to post a reply.
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#4
Yes a blackbox file could be helpful to determine the source of troubles, especially to see what P&I are doing on stick inputs.

There's 2 sliders below the PID table.
The upper slider adjusts how aggressively the copter tries to follow strong stick inputs - this one is very high by default, i recommend you lower it to around 1.0 or lower.
The lower slider is responsible for behaviour around mid-stick - it is very low by default, which means there's only little stabilisation (the copter feels loose) on small or no stick inputs.

Generally you'd probably have to increase P though. And I to a certain degree. Problem is, with the dterm sliders in a bad place, increasing I-term a lot could actually make things worse.
[-] The following 1 user Likes fftunes's post:
  • campagnium
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#5
Thank you fftunes, have been a bit on the busy side but after rereading you last post for the nth time I have figured out about the sliders and will implement your recommendations. When our weather is a bit more suitable I will test fly the quad and record a balckbox file then post it. We have and are having incredibly hot weather in my neck of the woods making tasks such as fly very uncomfortable.

Thanks again for the suggestions.
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#6

.doc   CLIDump060217.doc (Size: 23.5 KB / Downloads: 341) [Image: wkFpi1Nl.png]

Hello fftune and others,

I applied the suggestions form fftune and tested the quad. The results were not very good for me but I hope with the balckbox file can shed some light and set a direction for improvement. The first flight was very short and totally out of my ability to control. It was with the flight mode set to Air Mode thus the second flight was with Angle mode and hope that I could switch over to Air Mode once stable and airborne, was not to be as I was forced to land after maybe 20 seconds of a slightly more controlled flight but still terrible. I seemed to have very little control and the quad behaviour seemed to be  a couple of seconds of stick input.

The image above is a screen shot of the PID tab in BetaFlight, I hope it is good enough to be interpreted. I am new to attachments and seem unable to add the balckbox file
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#7
Hm not sure if bb logs can be attached. Maybe you have dropbox?

Short question, what motor protocol are you using, is it normal pwm or oneshot125 (on configuration page)? Because if the escs aren't capable of active braking it could be very difficult...

PS; just noticed, i-term seems very low at 25, i think you could double that, 50 shouldn't be too much.

PPS: and maybe put dterm transition (the lower slider) to around 0.5 for now... Those sliders can have huge impact on PID behaviour.
[-] The following 1 user Likes fftunes's post:
  • KonradS
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#8
Thanks for the reply.

With the ESC the protocol is PWM.

I have noticed that the BB files end in .bfl, I changed it to .TXT. Both formats work in Betaflight - Blackbox Explorer. I have attached the .TXT file and hope that it will get to you for a look at. 

Yes I have dropbox and can share files with you but I will need your email address, mine is [email protected]. I would rather correspond privately as I need to ask many questions but I don't know if a forum is the correct place.

Maybe I should add some context all I want to do is fly around I am not interested in racing as my reflexes are now far too slow. I have a farm so I can do the flying without bothering any one but I do not want to monitor what is on the ground. This is an exercise in keeping the brain alive.

I will implement your recommendations and let you know the result.

Thanks again

PS the system has told me that the file size it too big to post, so it will have to be via dropbox.
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#9
Blackbox test, I compressed the blackbox file and it seems the forum likes the size now. I hope so at least.


Attached Files
.zip   BLACKBOX_LOG_20170306_200226.bfl.zip (Size: 451.04 KB / Downloads: 173)
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#10
8/2/2017 Test flight in very calm conditions. Grabbed the opportunity to test the BR and surprise surprise it actually flew and was controllable, well sort off. 

It oscillates a bit and when it gets TX stick input it goes where it is pointed BUT it has to be corrected or it is off into the wide blue yonder. It won't come back to level flight so one has to be on the sticks full time. I landed after two minutes which would have to be one of the longest flights in the 65 tests/tuning flights so far. Thanks to fftunes I have more progress in a week than months of researching PIDs on the web and fiddling around on my own. The blackbox log file is too large to add to this post. 

PID data for this flight:
Roll P 60 I 50 D 10
Pitch P 60 I 50 D 10
Yaw P 80 I 45
D Set Point Weight .75
D Set Point Transition .5
[-] The following 2 users Like Hank Deucker's post:
  • campagnium, fftunes
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#11
That's good to hear, sry i didn't get around to check the last log.

The oscillating on stick inputs could be several things:
1) too high P (yaw P could be a bit high)
2) too low D (10 looks a bit low on roll/pitch)
3) too high setpoint weight slider (maybe lower this another bit first, from 0.75 to maybe 0.6 or 0.5)

Another thing you could try now: using another profile for further tests, say leave profile 1 as it is now, and setup profile 2 with slight changes. Profiles can be changed by stick commands while disarmed, so you can quickly compare one profile to the other in the field and see wether it got better or worse. To select profile, hold throttle low & yaw left, and roll left (profile 1) or pitch forward (profile 2) or roll right (profile 3). If you have a beeper connected it will confirm the change and the FC will also blink accordingly.

When you say it wouldn't come back to level, was this with angle mode enabled? I never use angle mode and can't look it up right now, but if this is the case, i think the value you are looking for is called "angle strength" iirc.
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#12
Thanks for the info, there is a lot to internalise and come to terms with. I will address one issue at a time, I will raise the D values to 15 for roll and pitch, then I will try the set point slider issue. By then my mind will be in melt down. Yesterday's test was with angle mode enabled, I will add it to my data next time.
It is just such a pleasure to get some help at long last as there seems to be no local help available. Thanks again.
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#13
You're welcome, i'm glad if i can be of help.

Do consider to use multiple profiles though, as it makes all the experimenting a lot lot easier, and you can quickly go back if things turn out to have gotten worse.

Maybe somebody else will have to assist on improving angle mode though, as tbh i simply have no clue about that... Smile
[-] The following 1 user Likes fftunes's post:
  • Hank Deucker
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#14
Hank, I had a look at your black box log and there seems to be a lot of vibration. Are your propellers balanced?

I'd also suggest that you proceed as follows:

Flash the latest Betaflight (release 3.1.6).
Set the craft up from scratch in Betaflight and leave all the PID settings at defaults.
Record a new black box log.

Betaflight has had a lot of improvements since the version 3.0.0 that you are currently running and it will fly most things pretty well on defaults.
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#15
Thanks to both fftunes and unseen.

I balance my props with a magnetic balancer as carefully as I can. The motors are supposedly balanced in the factory, I certainly do not have any equipment that would allow me to balance the motors. In the motors tab in Betaflight the line that shows motor balance is flat for each motor (individually) with out props attached.

I will flash the board with 3.1.6 and start all over again and maybe with all that I have learned I will get it done much quicker than up to now. 

fftunes recommends multiple profiles and sent a how to with stick commands. I fly mode 1 (thr on the RH stick) thus the commands don't work I am sure there is a list of mode 1 commands but my searches have failed to find one.

I live in what we call "the bush", I guess you would call it the country and do not have anyone close by I can call on for help the closest is 50 km (30 miles) away and they fly 250 mm copters thus seem troubled by 500 mm copters. To see them takes an afternoon and to coordinate that we are all available at the venue is quite difficult hence I rely to advice for forums, google searches and youtube videos and a lot of the information is contradictory. Thus I am grateful for the help you have offered so far.

As for blackbox files I can only attach any on this forum up the 450 kb. The size seems to be about 1 mb per minute of flight. Dropbox would be a solution but you would need to contact me by email via the forum so that I can 'invite' you to share my files.
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