yes I have the Pixhawk mounted in the center under the Shift.
I will delete the Auto mission, I forget it since 2019…
the swash is 90, but I will double check this is a good point!
Thank you
As far as I know, the blade must not move at all at this moment?
If the blade moves at this moment, the phase angle is not correct.
If your blade moves at the “pitch” input ±4 degrees, then the pitch angle is definitely not correct. It should not move at all.
We are talking about the blade that you have positioned exactly above the tail boom. It should not move at all when you enter pitch forward or backward.
The secret to all multi-blade rotor heads is proper tuning of the phase angle. This, however, is again very simple with the method blade over tail boom. I only fly scale helis with multi-blade heads.
BR
Heri
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Exactly, it appears there is significant phase error. That’s why I asked to perform this check, looking at the last log uploaded here, I can see symptoms of this problem.
Hi all,
as a newbie in ardupilot I try to read and learn as lot as possible and so also this thread.
By your last statement @heri and @Ferrosan you are talking about cyclic pitch, correct?
Maybe @flyingdragon moved not the cyclic but the collective pitch stick on his control.
Just only an idea.
BR
Juergen
@Juergen-Fahlbusch
Hello Jürgen,
I don’t think so, since he talks about ±4.7 degrees, which are typical values for a cyclic pitch. Typical values for a collective pitch would be e.g. ±12 degrees or -3 degrees to +12 degrees.
Grüße
Heri
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What a coincidence. Another thread just pointed out a youtube video on phase shifting.
Here the video: https://youtu.be/MH1emIx5Ubs
I always try to read all the posts in our subforum. This helps me gain more and more knowledge, even if I think the particular problem does not affect me.
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@heri I couldn’t understand why the response was so bad on both pitch and roll (the ATC values previously suggested should be good for at least a stable and controllable hover).
So looking at the rates, if you plot rollrate-desired and pitchrate achieved, you come to this:
and this:
the first picture shows the coupling between pitch and roll, the second shows a delay ranging between 0.5 and 0.7 s between roll desired and roll achieved (an eternity).
Now, pid tuning of course come into play, but the coupling seemed too much to me, so I thought to suggest checking the phase.
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@heri not sure if you’ve seen my talk at the Ardupilot forum back in 2021. I spoke about helicopter rotor dynamics in my talk. Here’s a video of my talk where I discuss details of helicopter rotor dynamics and the idea of rotor phase lag in the first 10 minutes of that talk.
Hopefully this doesn’t confuse the issue here. But it is important to understand that the 90° phase lag really only applies to teetering rotor helicopters that do not have any dampeners in the spindle. Most of the RC helicopters have dampeners, and in the multi blade rotors, the flapping hinge is offset from the shaft, which also changes the rotor phase lag, making it less than 90°. So what @Ferrosan is suggesting here is a good check of that mechanical phase lag built into the mechanics of the swashplate. It ensures that you at least have the phase lag at 90deg. In most cases to get a pure response for a given pitch or roll stick input, you may have to mechanically or through the phase parameter of the generic swashplate adjust the point of max/min cyclic pitch input to the appropriate phase lag of your rotor response.
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And in this specific case the head doesn’t even have dampeners, so it all relies on blade flexibility thus “virtual hinge” for flapping. The real Ecureuil rotor head features a central plate which allows for blade flapping, the so called Flex-Star. In this scale reproduction it is just a rigid component. So my suggestion of the 90 deg is just an initial starting point, can be optimized after .
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Ferrosan,
Thank you is not enough man!
you saved my Heli again!
I was wendering why every other RC AS350 head grib’s linkgage tilted!
after looking through the net, I see all of them have the Grib linkages tilted and they are not 90d
after changing the postion of the arms, I know see very very little movment when I rock the Syclic up and down!
and the two other blades to the sides moving with my syclic input
I attached pic you can see clearly that the pushrods are not 90d
you think I can perform a small hover and move forward?
I will of coruse re check all 3 blades tracking and the swash just to make sure nothing been off!
I apprecieate you and Bill efforts…
Ozzy
Check that at full swashplate movement the uniballs (especially lower ones- attached to the swash) are not hitting the mechanical limit.
Also check the control direction is correct:
-
place one blade over tail boom, set H_SV_MAN to 1 and place collective at 0 deg angle of attack;
-
apply full forward cyclic:
- front-right blade should increase angle of attack
- front-left blade should decrease angle of attack
- no-change (or at least very little) on the rear blade (over tail boom)
-
apply full right cyclic:
- front-right blade should decrease a little bit angle of attack
- front-left blade should decrease a little bit angle of attack
- rear blade (over tail boom) should increase angle of attack (largest angle of attack variation of the three blades)
Hi,
I set H_SV_MAN to 1 and place collective at 0 deg angle of attack;
the Mid stick was on -37% but this is not always the case, sometimes the 0.00 pitch on -53% or -74% stick movment and so on…
but that is not the case, let say the Mid stick 0.00 pitch was achived at -50%,
then when I push up stick (syclic nose down);
Left blade Right Blade
Yellow Blade : -5.1 -------------------------------------------Red Blade: +6.5
Blue Blade : -5.7 -------------------------------------------Yellow Blade : +6.7
Red Blade: -5.6 -------------------------------------------Blue Blade: +6.5
rear blades not moving.
then when I push down stick (syclic nose up);
Left blade Right Blade
Red Blade : +6.0-------------------------------------------Blue Blade: -7.9
Yellow Blade : +6.6--------------------------------------------Red Blade : -8.7 from-0.3 mid
Blue Blade: +5.9--------------------------------------------Yellow Blade: -8.8 from-0.4 mid
rear blade not moving
now for the right syclic;
Left Red Blade : -4.5---------------- rear Yellow blade +8.7-----------------Right Blue blade -4.5
note: I calibrated the swash plate and its 90 to shaft.
I also calibrated the blades by checking each blade’s pitch engle at one postion ( boom postion); I rotate each blade when its exactly on the boom, I read the pitch, and adjust all three linkages…
the problem I am facing is that when I move the thru stick or the syclic stick the blades never go back to the first postion ( original gage reading)!
its frustration! I.e: if I move the Thr stick to -44% to achieve 0.00 reading, then when I move it again and return back to -44% the gauge read another number +1.4 somtimes +2.3 or -1.5 and so on…
same when I center the Thru stick and move the syclic stick up and bring it down then center, the pitch gauge read different numbers each time I let the syclic go to center!
each time I move it give sifferent numbers!
I think its due to servo quality! servos must go back to the original point…
I don’t know its just crazy how this thing fly!
Sorry for the long reply
Thank you!
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@flyingdragon control directions looks good to me now, phase also. You might want to reduce a bit the swashplate throws, it appears you have a lot of tilt: you can reduce H_CYC_MAX parameter until you get around 6 degs of blade angle of attack at full right cyclic (instead of the current 8.7) on the rear blade (over tail boom).
Also check the stabilization works in the correct way, tilt the heli on roll and pitch, swashplate should lean against and sort of remain “level”.
Otherwise looks good to me for trying a small hover, but wait for @bnsgeyer check/green light too 
@flyingdragon
I agree with @Ferrosan.
I’m a little confused by this statement. Anytime that you use the H_SV_MAN in passthrough mode, the collective stick position (RC throttle stick) should always be in the same position at zero deg collective.
Which linkages did you change? The pitch links that connect to the blade control arms? I don’t think that is a smart idea as that will affect your blade tracking. Have you done blade tracking on his aircraft already? Blade tracking on a multiblade (more than 2 blades) rotor can be tricky but you definitely want to spend the time doing it otherwise you will have more vibrations.
I think with most of our RC equipment, there is some slop to the ball links. I know that my aircraft have it. I think when you are flying the blades always want to seek flat pitch and thus are always pressing down on the control linkages (at least for non aerobatic flying). So try pressing down on the control arms after every time you move the controls to remove the slop.
You should get a more consistent measurement.
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I already did the blade tracking to all 3 blades, I explained above my way to do that.
It’s just normal old school way.
I rechecked the awash level and it’s 90
So everything on table is good except the problem regard the servos positions
I am using Futaba system and it’s -100 to +100 pitch curve
H_SV_MAN 1
If I move the stick to the Mid stick ( Center of the joystick) will give me pitch value ~+4.5
If I try again it will give ~3.5
And if I try again it will give different reading
Each time the pitch gauge give different results./
I think that’s is servos issues… those servos are BK 8001
There is no slope in the servos or the arms. There is a very little play in the awash plate left and right
But that’s not the cause of that issue…
Anyway, I will test hover the machine today to see if there is any drift or any control issue…
Thank you
so which pitch links did you adjust to make all of the blades read the same value when they passed over the tail? I don’t understand.
I adjust the yellow blade and the blue, then re-checked the tracking to make sure all of them within .02 difference.
sounds good, I will reduce the Swashplate throws and fly it today and report any problem./
Thank you
I don’t understand. did you fly to determine that the blades were tracking or did you just do it through setting the pitch within 0.02?