91

General Discussion / Re: Dshot instability in 16.09+r782?

« Last post by TheOtherCliff on June 17, 2022, 11:59:40 am »

TPS has 3 sources: ActuatorDesiredThrust, StabilizationDesiredThrust and ManualControlThrottle, which one should I use?
I assume targets should be PID?

I use all the defaults (except for the curve itself) there.

92

General Discussion / Re: Dshot instability in 16.09+r782?

« Last post by TheOtherCliff on June 17, 2022, 11:55:40 am »

Autotune can cause problems with D-Term oscillation (invisible yaw oscillation).  There is a SystemIdentSettings->DerivativeFactor setting (no retune, just change this and re-save with the new PIDs).  If you notice motors are hot from just hovering, or short battery life (as compare to say using default PIDs), you may have this issue.

I mostly fly in stabilization on basic mode+ attitude  (or ins13+GPS modes)  and don't see any d-term values for attitude (expert) settings, is the above hint still refers to attitude mode?

When you are using AutoTune, you probably don't want to manually change PIDs by hand because if you ever enable AT again, the PIDs will be overwritten.

System -> Settings -> SystemIdentSettings -> DerivativeFactor
Click the red up arrow (Save) at the top of the window to permanently store it into your FC settings.
But then you must enable AT and use SmoothQuick to export this to the PIDs.

93

General Discussion / Re: Serial Receiver options

« Last post by TheOtherCliff on June 17, 2022, 11:46:35 am »

A little info about SBus protocol.  The standard SBus protocol is an inverted serial protocol.  There is a configurable hardware inverter built into LP compatible FCs on MainPort.  Inverting is enabled for SBus, so normal serial hardware built into the processor can be used with SBus.

I recall hearing long ago that there are some RC receivers (or FC's?) out there that skip the inverting, but that is non-standard.  Maybe FC's do it to avoid the cost of the extra chip on the FC or maybe the FC was designed without considering SBus.  The FrSky's that I have are all inverted, which is to say that they are "standard SBus".  I have several FrSky Rx's connected to LP FC's with SBus and they work perfectly.

So the question is what anyone means when they say "inverted SBus".  Do they mean the correct, standard way that actually inverts the serial protocol or do they mean doubly inverted which equals uninverted?

I would google the receiver in question and read a review or two or watch some receiver <-> FC setup videos to try to answer that.

Since you have your fingers deep in the code, you should be able to find where that inverter gets enabled or not.  A lot is driven by data structures.  If I wanted to order an SBus receiver and didn't know it's inversion status, I would just get it and make a version of code for it if it differed from normal.

94

General Discussion / Re: Dshot instability in 16.09+r782?

« Last post by Marico on June 17, 2022, 08:53:13 am »

AutoTune (and indeed any tuning) just tunes for the throttle you are using doing the tuning.  The solution is to use Stabilization->Advanced->ThrustPIDScaling to automatically increase PIDs at lower throttle and decrease PIDs at higher throttle.  Make sure that you start with what ever throttle stick position you were using being on the horizontal axis line.  That means at that throttle setting the PIDs will not be either increased or decreased.  From there you make lower throttle have higher PIDs and higher throttle have lower PIDs.

Test and adjust the graph (probably just a straight line with slope and above axis on left side / below axis on right side and goes through horizontal axis at the throttle you did the tune at).  Note that you can feel some wobble when descending straight down at medium speed the increases in PID for low throttle settings will help make that better, in addition to the reduction of PIDs at high throttle removing wobbles at high throttle.

TPS has 3 sources: ActuatorDesiredThrust, StabilizationDesiredThrust and ManualControlThrottle, which one should I use?
I assume targets should be PID?

95

General Discussion / Re: Dshot instability in 16.09+r782?

« Last post by trust on June 17, 2022, 07:29:08 am »

I think he is referring to the Derivative settings under the Inner Loop. Attitude mode uses BOTH the Rate Stabilization (Inner Loop) and the Attitude Stabilization (Outer Loop).

96

General Discussion / Re: Dshot instability in 16.09+r782?

« Last post by Marico on June 17, 2022, 06:28:56 am »

Autotune can cause problems with D-Term oscillation (invisible yaw oscillation).  There is a SystemIdentSettings->DerivativeFactor setting (no retune, just change this and re-save with the new PIDs).  If you notice motors are hot from just hovering, or short battery life (as compare to say using default PIDs), you may have this issue.

I mostly fly in stabilization on basic mode+ attitude  (or ins13+GPS modes)  and don't see any d-term values for attitude (expert) settings, is the above hint still refers to attitude mode?

97

General Discussion / Serial Receiver options

« Last post by trust on June 17, 2022, 03:24:09 am »

OrangeRx receivers - at least 8 or 9 channel with s.bus output - don't seem to be available anymore.
Spektrum offers SRLX2 output - can this work with the SRXL configuration on Librepilot?
Frsky offers S.bus, but it's inverted? Is there an option in configuration to use inverted?
I have both a TX16S and a Futaba T9CHP with a Spektrum module (old DSM2), so I can use pretty much any xmtr format. But I really prefer the serial outputs to feed into the flight controllers. MUCH simpler hookup.

98

General Discussion / Re: New Release "Within the next several months"

« Last post by trust on June 17, 2022, 03:15:02 am »

Most of our aircraft are the Hellaplane bimode variety with v8 of our customized Librepilot code, but I do have a quad which runs unmodified Next.
I'll help when I can.
Ironic that you should think of Lazarus as the name.
That was the name of my CG mfg and production company back in the 80s - Lazerus Productions
It came from my notoriety as LASER Rust
Back in those days I built the world's first LASER 3d full color video projector (wall sized images 25'x14') , first 3d computer generated hologram for the cover of SIGGRAPH art show catalog - among other wild and crazy machines.

99

General Discussion / Re: Dshot instability in 16.09+r782?

« Last post by TheOtherCliff on June 16, 2022, 10:51:36 pm »

OK, I did  autotuning with 4S and now flying with 4S is smooth but only in lower-middle throttle range. On high throttle quad  gets wobbling and props sounds like get high turbulance.
...
Does autotune may help with tuning to get rid of that wobbling in high throttle? I noticed that practically autotune "tune" always in low throttle (need quad to hoover), so how get proper tuning in high throttle ranges?

AutoTune (and indeed any tuning) just tunes for the throttle you are using doing the tuning.  The solution is to use Stabilization->Advanced->ThrustPIDScaling to automatically increase PIDs at lower throttle and decrease PIDs at higher throttle.  Make sure that you start with what ever throttle stick position you were using being on the horizontal axis line.  That means at that throttle setting the PIDs will not be either increased or decreased.  From there you make lower throttle have higher PIDs and higher throttle have lower PIDs.

Test and adjust the graph (probably just a straight line with slope and above axis on left side / below axis on right side and goes through horizontal axis at the throttle you did the tune at).  Note that you can feel some wobble when descending straight down at medium speed the increases in PID for low throttle settings will help make that better, in addition to the reduction of PIDs at high throttle removing wobbles at high throttle.

I'll try change props  from 5x4.99 to 5x3 (250 frame) and test it again.

Of course you should retune if using different props...

That strange that little volt change 3S->4S with same battery weight (I use different bat capacity when switching beetwen 3S/4S to preserve almost the same weight) makes that big difference in quad (in)stability....

Decreasing voltage by 4/3 decreases power by roughly (4/3)x(4/3) = 16/9 or about a factor of 2.  Decreasing power by a factor of 2 makes it accelerate it's flips only half as fast and requires PIDs to be reduced by about a factor of 2 (if I recall the math correctly) to avoid oscillation.

Thirst I did autotune with default PID with 3S then I used new PIDs (for 3S) to autotune with 4S...

As I recall, that should work OK.  3s will have lower PIDs, so it is OK to tune 4s with them.  I personally always do AutoTune using default PIDs if they work well.

As I understand how SmoothQuick works: it just change in +- PID values in some range, but changes I see (not tested in real flight yet) are very low to work with my quad, I think. When I tested PIDs manually I didn't see any differ when values (in attitude mode) are for an example 4,6 or 8,5: quad behaves the same...

I see a very noticeable difference between Smooth and Quick.  Smooth is good for taking video.  Quickest can even have slight wobble (I use self stabilizing mode like Attitude).

----------------------------------

Autotune can cause problems with D-Term oscillation (invisible yaw oscillation).  There is a SystemIdentSettings->DerivativeFactor setting (no retune, just change this and re-save with the new PIDs).  If you notice motors are hot from just hovering, or short battery life (as compare to say using default PIDs), you may have this issue.

100

General Discussion / Re: Dshot instability in 16.09+r782?

« Last post by Marico on June 16, 2022, 09:50:13 pm »

Using a different voltage battery needs a different tune.  Using a heavier battery or adding a camera or using different props needs a different tune.  The Stabilization tab has 3 PID banks in it.  You can store the different PIDs there and make different FMS switch settings use different PID banks if you want.

OK, I did  autotuning with 4S and now flying with 4S is smooth but only in lower-middle throttle range. On high throttle quad  gets wobbling and props sounds like get high turbulance. I'll try change props  from 5x4.99 to 5x3 (250 frame) and test it again. Does autotune may help with tuning to get rid of that wobbling in high throttle? I noticed that practically autotune "tune" always in low throttle (need quad to hoover), so how get proper tuning in high throttle ranges?
That strange that little volt change 3S->4S with same battery weight (I use different bat capacity when switching beetwen 3S/4S to preserve almost the same weight) makes that big difference in quad (in)stability....

Autotune has SmoothQuick adjustment that you might want to play with.  AutoTune should always be run using PIDs that do not oscillate (default PIDs usually work well).

In my props/battery config default PIDs with 4S generate high wobbling even in low throttle. Thirst I did autotune with default PID with 3S then I used new PIDs (for 3S) to autotune with 4S...
As I understand how SmoothQuick works: it just change in +- PID values in some range, but changes I see (not tested in real flight yet) are very low to work with my quad, I think. When I tested PIDs manually I didn't see any differ when values (in attitude mode) are for an example 4,6 or 8,5: quad behaves the same...