Betaflight - Fix Wobble with Thrust Linear

A review of the Betaflight Thurst Linearization feature.
PR: github.com/betaflight/betafli...
New PR: github.com/betaflight/betafli...
Excel sheet: tiny.cc/uavtech
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[@h2o-fpv623]

Great will try this as well thank u so much for ur work to teach and show us this information.

[@edouardmalot51]

You got a new patreon ;) Thanks for all this works

[@TMacFPV]

Good stuff! I like the fact you pointed out it was most useful for low T/W quads. Its my understanding its great for whoops with a suggested value of 70-100! I'll be trying this out. Thanks Mark👍

[@tehllama42]

Most precisely it's low motor:prop authority quads, but that tends to come with low thrust to weight ration accordingly. A lot of tuning around the low throttle on that end would make stuff edgy when pushed hard (you can think of TPA as a ghetto two-point trapezoidal interpretation of the idea)

[@ungravityfpv]

you´re great dude! huge thanks for your content!

[@pt0x]

Great stuff. Will try this out soon. I'm running 24kHz now on my quads with 4.2 to overcome the wobbles, but highly prefer to run 48kHz

[@uavtech]

I know some folks used with 48khz with success.

[@KCQuadTronX]

thanks for another great video!!!!!!!!!!

[@yolofpv2936]

Nice content! 👍

[@moejammin]

Thanks for the reply. I do have D_min turned off. With stock settings it has a weird side to side wobble that I was able to make a little better but it still has a wobble at certain throttle points. I had thrust linearization on, I think it helped a little.

[@LuisCruz-op7kx]

@UAV Tech you have a edit issue, where you say the same twice, and funny awkward silence :D thanks so much for all the effort :)

[@uavtech]

Just saw that. Missed taking out the first cut. That's what happens when you rush! Oh well.

[@scissorzz]

Just smashed the like.

[@vicewize]

Awesome!

[@ProjectMockingbird]

BF Whoops like 50, FWIW. Another great Silverware feature!

[@conditionisin8918]

Hay haven't tried it yet but sounds reasonable! Fyi I was lucky enough to stumble apon this help by looking up desinc. It may help your views/ help others who bought an overproped quad/ installed 4.2/ by giving a more generic title/ link to your Info, like quad wigs out at WOT wide open throtte or something. Thanks tho! Very helpful!

[@princesfpvdrones]

Utterly brilliant, can't wait to try this on my 7" bobble issues!

[@tehllama42]

Yup, it helps. Do hop onto the UAVTech Discord - a few of us have 7" rigs and setups that are working quite well

[@princesfpvdrones]

@@tehllama42 I am on discord. I am go by the username: Princecord

[@princesfpvdrones]

Lets get in touch?

[@tehllama42]

My username isn't wildly different ;)

[@princesfpvdrones]

@@tehllama42 What is your username?

[@Krunked]

Sweet. Ive been employing thrust linear of 25 to arrest throttle chop wobbles when using 48khz... Works well!

[@Nikita-zd1gc]

same trouble while doing powerloops(3 inch 48khz). hope 15-20 will work for me. thanks

[@tehllama42]

Yeah, similar data points - 7" on 48kHz is definitely happier in the 25-33 thrust_linear range, the over-motored ones are happier with lower values, but the smaller (2507, 2408) ones need a bit more there.

[@jmcinematics]

Is this on a 5 inch quad?

[@Krunked]

@@jmcinematics yes I use it on 5inch too. If I'm. On 48khz

[@tehllama42]

@@jmcinematics 7", 6", 5", and 3" I run this. For my 3-5" racing rigs, I don't bother with thrust_linear, although it probably wouldn't hurt.

[@kandredfpv]

Hey Mark, this is awesome. I'm glad you've done a video on this feature because I started using it when it first came out in 4.0 and IMO it really improved the performance of all my 5" quads. But at some point I upgraded to 4.1 and found I was getting low throttle oscillations which went away when I turned off thrust linearization. For some reason I had also disabled TPA (by setting tpa_breakpoint = 2000) when I enabled thrust_linear = 50 (the recommended amount on the original pull request). But I noticed in your video that you never mentioned disabling TPA, and for the life of me I can't find where I got those instructions from. Interestingly earlier this week I discovered that my best flying quad still had a thrust_linear = 50 (with TPA enabled) config! That may explain why I thought the tune was so perfect. So, is thrust linearization a replacement for TPA or do they work together?

[@uavtech]

They are are kind of similar but different. Since TPA is D-only now by default, that is the biggest difference unless the user changes back. Also TPA is linear after breakpoint. Thrust linear is not.

[@moejammin]

Thanks for the great video, would you have any idea(besides me being horrible at tuning) why my quad flies great on BF 3.5.7 but is pretty wobbly on 4.2.2 with rpm filtering?

[@uavtech]

Turn off D_min. The default pids on 4.2 are lower than 3.5.7. Raise them up (P & D Gain Slider).

[@MrBirdshell666]

finally!

[@Quad66]

Has the function that generates correction been updated? Specifically if I’m reading correctly the function is curvilinear with the inputted value acting as a curvature constant rather than a scaling term. The APC data on the other hand (and the 5 inch quad response) suggests a sigmoid function, maybe a fixed one that is scaled? github.com/betaflight/betaflight/pull/7304

[@ibnfpv]

great ! dose it overwrite the TPA? it's like curved TPA basically? that can adjust the curve

[@uavtech]

Yeah, basically.

[@flo-ridafpv5713]

ALRIGHT......thats my que to click like ;)

[@ti2phol]

Hey Mark, I am having that issue 6:43, where you chop the throttle and get that wobble on pitch axis. Its very pronounced when you do power loop where you chop the throttle and bring your pitch stick to center.. i get that bobble in th pitch axis. I cant get rid of it. Need help, thanks.

[@uavtech]

Did you tune PD Balance and push up PD Gain till you get oscillations and then back it off a touch?

[@ti2phol]

Sorry Mark.....

[@flaparoundfpv8632]

Right now I'm using dynamic idle and a very high min throttle percent to fix the bobble issue. Would you recommend I turn the percent back down and try this instead?

[@uavtech]

Might be worth a look. Wobble is a low PID authority issue.

[@flaparoundfpv8632]

@@uavtech Tried it on two rigs, but was only able to reduce the idle percent by about one percent. I've been loving 4.1 and 4.2, but I've been very frustrated by how the devs have relagated all quads greater than 5" to the realm of "low authority". The pursuit of perfect 5" setpoint tracking has really caused the project to move in a narrow-focused direction.

[@divingfalconfpv4602]

your default starting tune post you said 25 right? I have 3" and below

[@uavtech]

Yup

[@ripperfpv9880]

hi mark i have put your preset in the gt369r and i am getting a fluttering noise any help would be greatly absorbed thanks

[@uavtech]

Reduce P and D Gain slider.

[@jmcinematics]

Do you post the video of the nose dipping on KZbin or only on patroen?

[@uavtech]

It will be on Patreon only. Kind of a special.

[@fpvpf]

Hey Mark, great video..Thx for the help. One question...I am running 24 kHz...Is it ok (safe) to use with 24kHz or i should change pwm to 48 khz....Thanks

[@uavtech]

24khz is good.

[@fpvpf]

@@uavtech Thx Mark. i really appreciate your support for the fpv community.

[@tweekFPV]

👍👍

[@tylerwilliams786]

I went to betaflight 4.2 to test,and ever tune and filter setting i get hot motors. I am using the radix li. I went back to betaflight 4.1,and all is fine. Is there something new I am not doing.Or is 4.2 not stable yet. Thank you for all you do for this hobby👍

[@uavtech]

Best advice I can give is something is getting messed up in your settings somewhere along the way because 4.2 = 4.1 with a couple more features. All the filter and PID stuff is the same. Been using for a while and so have many (thousands) of others. Maybe a DIFF paste is getting it messed up for some reason? In either case, 4.1 has Thrust Linear as well if you just want to not mess with an update again and play with Thrust Linear.

[@tylerwilliams786]

@@uavtech thank you,i will reflash. Think I am going to try new flight controller. Because on my other quad with f7 fusion it is ok. guess it is part of hobby. I will figure out soon thank you for your time👍

[@tylerwilliams786]

@@uavtechJust wanted you to know it was not betaflight. I updated crossfire firmware,and all is fine now. 4.2 after your last video i got it as they say locked in. A course using blackbox. Again thank you

[@jorgeromero4680]

in one part of the video you talk about over prop. Can you do a video please on how to choose the "right" prop please? if that would be possible. thanks

[@tehllama42]

That's a somewhat complex subject, because there are different things you'd want, especially as related to stator size. I can usually give people a short list of props to try though.

[@leflamantrosefpv1725]

@@tehllama42 take 20 pack of different props, and test it one by one.. when you have the 2 or 3 packs are ok, (good motor + good prop = good quad) and keep the big pack of 20 with no crash, and when you have a news motors or new quad, you have all this props to match for your quad.. ;)

[@vincertron]

Does bf 3.5.7 not have thrust linearization ?

[@uavtech]

No.

[@RixFPV]

What does "over propped on the motors" mean?

[@uavtech]

Angle to steep or disc area too big. Motor can not put out enough torque.

[@RixFPV]

@@uavtech Thanks!

[@Kalandro99]

Interesting technical insight as always! Forgot to cut that transition? xD 6:47

[@uavtech]

Lol. Whoops!!!

[@ehunter2010ed]

If I'am using a taranis xd9+ running crossfire shot newst FW but I have been running a older open TX FW would this effect my flight characteristics?? Or would it not sense I'am using crossfire shot?? I've heard that as long is I'm using crossfire it wont make a difference & doesn't matter what version open tx i'm using!! Asking because I was watching rc smoothing video you produced about a year ago & u didn't mention what I'm asking now!! On BF 4.2 if I run rc smoothing under receiver tab 50% flys good not perfect but really good compared to if I leave it at stock 10% I get so much bubbles & stutters!! I even checked my smoothing under cli when it's at 50% all the way max & it's 6.677 latency I haven't checked yet with it turned to stock%10 yet!!

[@divingfalconfpv4602]

Shit I did the Thrust linear 25 but i also raise tpa .65 to .5 and breakpoint down to 1250 where wobble oscillation started. wonder if thats too much doing both. its Rekon7

[@itsfpv2561]

Hi Mark, didn't thrust linear exacerbate D term grinding at low throttle?

[@uavtech]

Drops off at very ends.

[@tehllama42]

The actual part to be concerned about is if you have a craft that is otherwise prone to D-term oscillation to-the-moon conditions, thrust_linear won't help there.

[@Sugar_K]

@@tehllama42 it totally does but..... you can lower the Dterm min lpf.. and then use the dynamic dterm lpf expo to get back your phase delay while having a lower based Dterm lpf.. very cool and as close to a free lunch as you gonna get

[@tehllama42]

@@Sugar_K Yeah, particularly on larger quads, running the DTerm Filtering Slider all the way down to 0.85, but using the dt-dlpf-expo to get that quickly out of the way, I've been seeing some pretty excellent results. Still a bit over-filtered, but I'm able to run the P&D gain slider up in the 1.6 range without much in the way of thermal issues for under-motored setups (i.e. on 4S my 7" floss is solid, but I can run 6S at race pace without burning to the ground)

[@TheBooninator]

@@uavtech fwiw, in an attempt to understand the code and where that drop off comes from, I asked about it in the betaflight slack. ctzsnooze stated "I have no clue what your spreadsheet is doing but actual PIDs don't do that." I tried to explain I thought it was his spreadsheet, but.... Anyways, it's now my understanding that the drop offs at the very ends of throttle range do not reflect the reality of the code. I suspect it's because the spreadsheet doesn't simulate air mode (modified throttle is simply constrained to a 0-1 range.)

[@Sugar_K]

lols that one down tick is from Kevin at Emu

[@uavtech]

Jokes on him (or whomever). Still counts as engagement! :-)

[@Sugar_K]

UAV Tech 😂

[@DronePlayground]

👍👀🇭🇷

[@hugochiang1072]

LOL I'd like to join your patreon but no visa card.

[@uavtech]

Boooo... ;-P

[@robsonchaves4661]

You didn't show it...

[@uavtech]

Show what?