Trex 600 stretched (700) Pixhawk 3DR tuning

Perfect I will go ahead and copy these parameters

Regards the P and D for the roll axis ; sorry for any confusing I caused , I was messing with them lowering them to 0 thinking that the VIB at the roll will be gone .

I will copy your values and report back With new flying log

Thanks a lot for fallowing up with me!

Be aware that the Pixhawk 2.1 is sensitive to wrong mounting!
In March I changed my FC to save some weight and it worked.
Read this: Flybar 450 Heli in loiter mode

Thanks a lot for the link thats a rich information everybody need it, I am going to write all the notices down to make sure I Am going in the right road! If any symptoms appear !

As of the location; that is why I like big ships just to give me different options to mount the FC but on the 450 size kinda hard to find more spots.

After placed the shaft on a Magnetic V block
It was 0.0001 very nice !

Next step is making third bearing block…

Step after : flatten the main gear and the autorotation gear using AAA surface plate

The final step will be tighten the bearing blocks the way can pull each bearing from other side to make sure the shaft set snag !! No play

Thank you

I had to scrape the Hub to get tight runout, but the main gear turn to be in a good shape, but since its plastic will give and take and unfortunately will wobble!!! there is no way to stop that wobble!

I also tightened the both bearing block to pull the shaft into each side, but I didn’t put the third bearing block since its not here yet! but now the shaft is solid no movement, it was night mare to get these couple things right!

now I lowered the P gain from 0.015 to 0.01
and got the result bellow! I don’t think this heli will give better result in Freq oscillation! just tried every possible thing, and came up with few things from my own! like putting washers between the frame one side only to each bearing block, also add home made washer under the bearing block to clear the main gear from touching the frame things like that!

I didn’t change the Freq to 20 because I replaced the Main gear and now its 110T instead of 112T so that will give me more RPM, I also ordered 16T pinion instead of the current one 14T
that way I can get nice 1500 RPM and control the RPM from the setpoint!?

Please can you tell me if I am ready for the next step after hover trim and my heli now fly nice and almost hand free!

Thank you

parameters after scraping the Hub Aug-29-2019.param (14.1 KB)

Hi Ozzy,
I looked through the parameter file that you supplied and it’s not exactly what I requested you to fly. Is that what you flew in the log files?
Please fly configuration I requested. Thanks!

By the way, it is not the frequency of the notch that I’m am concerned about. It is that you used different settings for ATC params than what I requested.

Oh so sorry that was big mistake! I loaded the old parameters instead of the new values !!

Will fly it again today with the new parameters and values you posted here !

I appreciate that

Edit; here is the new logs for the new flight
Thank you so much!

new parameters AUG-29-2019 925AM.param (14.1 KB)

I did a little experiment tonight with my helicopter. I did two flights, one with blade bolts lightly tightened and the other with the blade bolts very tight. With the blade bolts very tight, you can definitely see the difference in the aircraft vibration from the data. This is the roll axis for the loose blade bolts

This is the roll axis with tight blade bolts

The big thing to note is the higher frequency noise in the roll rate signal. You also can see more oscillations in the data which is about 3.5 to 4 hz.

Looking at the pitch axis, you don’t see as much noise in the data between the two but you do notice the 3.5 to 4 hz oscillations becoming more pronounced. I would have never guessed that the 2/rev vibration would have affected the lower frequency oscillations.
Pitch axis with loose blade bolts

Pitch axis with tight blade bolts

So Ozzy, are you making your blade mounting bolts really tight or are they being restrained some way from being able to swing forward and backward? So I don’t have a good way to tell how tight to make those bolts. I would say that they should be tight enough to keep the blades from swinging back during a slow rotor startup. If they are so tight that if you were to tip the heli on its side with the rotors parallel to the ground and they don’t swing down, then that is probably too tight.

Hi Ozzy, with regards to this comment. Can you confirm that you are using a throttle governor on your speed controller and not just setting a single pwm value without a governor?

Hi Bill, thanks a lot for posting pics showing the different between the two flights!!

I can see now the freq-oscillating! Even when you tight the blades still your Rate better than mine!!

I tried all methods regard the blades

I have had tightened them, and loosen the blades and based on the size of the blades 710mm I had to make it in between tight and loose, and I use the old method by hold the hole and shake it little bit to see if the blades move …

But I am thinking maybe the front TT gear mash is not loss and can cause that!

But can you check your heli and see if you have wobbling main gear and autorotation gear ?

I have normal amount of gear wobbling and you can’t fix that, but if you have main gear wobbling that will tell me it’s not that who causing the vibration !

I run it today on the bench with head and complete tail removed
Instill see some freq oscillating!

I am Changing the cyclic servos to BK 8001

And just to make sure it’s not servos causing that!

Mate ; you brought nice point here
I have had calibrated my HW 130 opto and got it set then I assign ch 8 for throttle, basically hit the switch and the speed go to what ever max is

Now I just replaced my main gear to 110 t and changed my pinion from 14 to 16t

That will increase the head speed to ~1500

440kv 10 pole
6s 60c 5000 mah
110 main gear
14 pinion
130 A hw v4 opto esc

Thank you guys for the help !

Based on your last flight. Pitch is not following as well as I want it too.
Halve your P and D gains on your Pitch axis only. Then raise the ATC_ANG_P to 6 in 0.5 increments. Post a log with the ATC_ANG_P at 6. If it feels good in pitch with ATC_ANG_P at 6 then try loiter for 30 seconds and see if it holds position without toilet bowling (wandering about).

What do you mean you don’t like my pitch ?? Is that the freq oscillations? Or not tracing the des pitch ?

I will halve he values and try the loiter mode

I am working on smoothing the mash gears between the red gear umbrella and the front red gear

Hope I can lower the vibration! Otherwise there is no way I can get it lower than I less if I machine metal main gear !!!

That will be to much !!

I will report back with logs

I appreciate your help

It’s not tracing the desired pitch very well. I also noticed the oscillations. So I am having you halve the P and D gain to help reduce the oscillations. And I am having increase the ATC_ANG_P. That should read ATC_ANG_PIT_P in the previous post. Having you increase that to help reduce the error and have the actual pitch attitude trace the desired better.

Make sure you get me some data in stabilize before going to loiter with the new ATC_ANG_PIT_P.

Hi Bill,

I was able to get the ATC_ANG_PIT_P,5.5 with no problems and I tried the loiter mode… its solid in the sky, but the collective is weird!

I will try the 6 today

when I switch to Loiter and I am already about ~1+ collective pitch the Heli want to sink down and land so I had to give more + collective to keep it up to the point that I need to lower just a hair then the heli stay there then if I switch to Stab it will go up and I had to lower the collective !

like you see in the logs, it land itself couple times because I was about +1 collective or so…

but there is no toilet bowling at all.
here is the logs and the bin I flew it on STAB mode then switched to loiter mode.

I appreciate your time helping me!

loiter test mode.param (14.1 KB)

your problem can be fixed with the param. IM_STAB_COL_2 and _3.
Chris Olson is explaining that in his video ArduPilot Trad Heli setup video2.
You can forward at about 16 minutes than that subject starts. At about 20 minutes he is talking exactly about your experience you have at the moment if you do not adjust those param.s to the right values.
Good luck.

1 Like

I did copy the video and did exact thing what Chris recommend
But my mid stick is 3.3+ not 0.00

My stab_col 2, 550
Stab_col 3, 650
Now my max is 11+
And my min is 2.6 -
The 0.00 collective will be on the first 1/4 stick

And that what make me thinking and asking why he want the mid stick to be at 5.5+ and not 0.00 so that be easy for me to leave my stick to mid center when I want to switch between any mode !??

Now I change STAB_COL 2, 575 and STAB_COL 3, to 625

And when I was hovering on Stab over 1/4 stick then switched to loiter mode the heli smashed into the ground !!

So why you don’t have 0.00 on mid stick( center stick) not on 1/4 stick thats for STAB mode
Also on passthrough mode …

So that he heli will return back to level wen I have my stick on center mid 0.00 !!

Again my setup is;
Pass through mode max : 11+ Mid; 0 min:0

Stab mode max : 11+,
mid stick ( center stick) : 3.3+
And the 0.00 on 1/4 stick
And the 2.6- on bottom (lower stick)

Please correct me if I am wrong

Here is pic of my 0.00 collective

Thank you

Chris is saying in his video that his Heli needs 5.5 degree + collective pitch to hover at mid stick with all the extra weight the Heli is lifting. That is quite a bit. In the past we called that a bit under-powered Helicopter. 700 was to much and dangerous. That is why there is a warning when you put in more than 500. You maybe need only 450 or so.
Now the Autopilot needs to know that when the Heli is hovering at mid stick. 5.5 = 550 in IM_STAB_COL_2 in Chris,es case. In your case it should be 330 and not 550 if I see your value of 3.3 degree hovering value at mid stick.
If you now switch to Alt Hold at mid stick the Heli will not go up or down.
The same when you switch back to Stabilize at mid stick.There is No going up or down.
I also have IM_STAB_COL_1 set to 0 and _4 to 1000. It works with my Helicopters!

I re set the values of IM_STAB_COL_2, 330 and the IM_STAB_COL_3, 550

hover it at less than the mid stick then switched to loiter and smashed the ground hard!

then I rechecked the collective at mid stick using the manual mode and it was 3.9+
so I changed the IM_STAB_COL_2, 460 and flew it, I was able to get really slow diving or climb up, so I had to move my stick to find where is the heli will stay there! but I was not able to make it stay there easy! so the stick was about above the 1/4 stick!!

I also notice very small amount of toilet bowl !

it was not nice steady there !

Thank you

I haven’t watched Chris’ video. But I know why he wants mid stick to correspond to 5.5 deg collective blade pitch. So think of the IM_STAB_X as a way to independently set your collective pitch in stabilize mode. Remember that ALT_HOLD, LOITER, and POSHOLD control the collective for you to give you vertical rate based on your stick position. Now there is a deadzone for the stick position in those modes called THR_DZ. In stabilize and acro, the deadzone is handled with the RC_3_DZ.

Ok so the 0 to 1000 values in IM_STAB parameters refer to the collective stick position where 0 is H_COL_MIN and 1000 is H_COL_MAX. IM_STAB_1 sets the collective position for the RC transmitter throttle stick on the bottom in stabilize mode, IM_STAB_4 sets the collective position for the throttle stick on top (all the way up). IM_STAB_2 and IM_STAB_3 set the collective position for the throttle stick at the 40% position (just below mid stick) and the 60% position (just above mid stick).

So if you set your H_COL_MIN and H_COL_MAX so that the collective blade pitch for a hover is half way between those values, then you should just set IM_STAB_2 and IM_STAB_3 to 400 and 600. That will give the stabilize collective output a direct relationship between the stick and the collective blade pitch. Mid throttle stick on the transmitter will correspond to the collective blade pitch half way between H_COL_MIN and H_COL_MAX.

H_COL_MID is used for other features like collective to yaw mixing and allowing the flight controller to know \when the collective blade pitch is low to set the landing complete flag.

So based on your setup above. I would set your IM_STAB_2 and IM_STAB_3 to 400 and 600. then when you check your collective blade pitch in stabilize, you should read 3.3 deg with the throttle stick at mid position.

Bill, thank you so much for the details Explanation!
I will try the 400 and 600 today, now my question is when I let say hover the heli and my stick at that moment was little above the 1/4 (40% stick) then I switch to loiter mode

The heli should not go down or up? Right !

In my case now I had to move the stick little bit up to get the heli up then move it little down till I adjust the heli to stay there !!

Is that normal or that should not Happen at all?

What I understand from your post is that the setting will correspond to all other flight modes and read the different in the CP ( collective pitch) and see where is the heli on that moment in those degrees

Let say if I hover at 40% stick and switch to loiter then move the stick all the way up 100%
The heli should not go up ?!

And if I move the stick rapidly down 0% nothing will happen?

BUT the moment when I switch back to Stab mode the stick need to go back to 40% stick before I hit the Stab switch ?
To make it ready for the Stab mode to take over

But if I had the stick in that moment at let say 60% the heli will jump up ! The moment I switch to STAB mode!

Thank you so much