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Tail rotor tune problem
« on: November 24, 2019, 11:46:55 am »
Hello Everyone,

Nowadays I am dealing with Mini Heli Project and I am having some troubles.

My setup;
- Autopilot:                   Revo Mini
- Frame    :                   XK K110 FBL 120 degree swash plate
- Main Rotor Controller: Brushed Speed Controller 5 Amper
- Tail Rotor Controller :  Brushed Speed Controller 1 Amper
- Receiver :                  FrSky XM Mini Receiver Sbus
- TX:                            FrSky Taranis X9D+

Here is my problems regarding the heli,

I applied all of the calibration and setup procedure. Everything seems to perfect and autopilot is doing its job to stabilize heli.

1st Problem: As soon as battery is plugged, main rotor and tail rotor start to spin at full throttle. After one or two seconds, main rotor stops to spin however, tail rotor continues to spin. How to prevent that, I want them spin as the autpilot armes.

2nd and the most important problem: I think that tail rotor can not adjust the RPM or Thrust to ovrecome main rotors torque.Therefore it is continuously rotating. Suprisingly, It flew but it is flying like a flywheel :). I will attach a video you will figure out more precisely.

What I have done to overcome these problems,

TxPID is set up and I tried to change PID settings while flying, There was some improvement yet rotation problem still stands.

Different combinations of flying modes are applied and tried as flying nothing changes. Still if you have suggestion to overcome this problem I will be happy to hear them.

Thanks in advance. I really want this heli fly.

Edit: Attachment did not work, here is the link


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Re: Tail rotor tune problem
« Reply #1 on: November 25, 2019, 03:37:07 am »

Spins up as battery is applied...
How do you arm it?
Is it set to Always armed?

For the tail, will you control the yaw by changing the tail rotor rpm?
The tail rotor is fixed pitch right.

can you upload the video to YouTube and post the link here?


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Re: Tail rotor tune problem
« Reply #2 on: November 25, 2019, 07:13:17 am »
Hello Karla,

Thanks for response.

Yes my heli has a fixed pitch propeller at the tail rotor. We are trying to control yaw by changing the tail rotor rpm.

No it is not always armed. I delegated a switch on Transmitter.

Here is the youtube link


Re: Tail rotor tune problem
« Reply #3 on: November 25, 2019, 08:41:54 am »
Some comments:

One time in the video, I saw that you were able to almost stop the yaw spinning in flight.  At that time, I think I saw some oscillations.  You might want to reduce your PIDs if you notice oscillation.

You might try setting the yaw to manual for a test.  When flying that way, you should be able to prove that you can make it spin either way and maybe even trim it to be not spinning much.  If you can't, then you have a problem that the FC can't fix if even full manual can't make it stop spinning.

Since you added the FC, if this is a lot heavier than it was designed to be, then are you running with a lot more main blade pitch/RPM to get it to lift the extra weight?  And if that is true, then it is generating a lot of extra torque that the tail rotor must be able to fight.  Maybe the tail rotor is just not strong enough to fight the extra torque?  That manual yaw test should tell you if this is happening.


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Re: Tail rotor tune problem
« Reply #4 on: November 25, 2019, 09:15:15 am »
Thanks for all answers,

What we figure out is , tail is dominating all of combined torque. I set the PWM value 490 to 300 and now getting much more reasonable attitude in manner of yaw rotation. But PIDs need to calibrated. Because of jiggly and non controllable flight.

Besides that originial flight weight is 46 grams. What we have done right now, 47.55 to 52.00 grams depends on battery.

So not much weight change in my opinion but still I am sensing the torque and governor needs.


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Re: Tail rotor tune problem
« Reply #5 on: November 25, 2019, 10:03:51 am »
Thanks for sharing that video, really helps.
I get very stressed watching it since you are so close to the walls with tail and main rotor.
You hit it several times but seemed to have gotten away with it, for larger helis just a slight touch and you are gone repairing for a week. Can you please find a larger place to fly! like a gym or something.

Anyway, you seem to be doing good because the stabilisation roll pitch seems very good!
The little problem here is the yaw control - lets fix that.
b t w How do you control it, via a smartphone? Scary.

This is my thinking, as the rpm of the main rotor increases and you get lift off and hover, the torque will increase and the need for the tail to counter that. So the rpm of main rotor has a relationship of the rpm needed on the tail - right. Just setting a fixed rpm to the tail and expect it to handle the Heli in different head speeds (rpm of the main rotor) will not work well. So, at the moment how do you change the rpm of the tail rotor?


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Re: Tail rotor tune problem
« Reply #6 on: November 25, 2019, 10:25:02 am »
Hello Dear Karla

We have a fixed pitch tail rotor and brushed speed controller to control it. As the yaw rotation increase, tail rotor rpm increase as well (depending on the rotation way, of course). So that, It is trying to compensate the overall torque.

However, As we understood, tail rotor thrust is too high that even the lowest pwm value is higher than the overall torque. We set tail rotor pwm to lower value. Now, we have a considerably ok yaw stability but we need to enhance other axes. We are planning to do setup and calibration procedure all over again to not to miss anything. And another video with corrected tail rpm is on the way. Video's title is agony of the mini heli!

Consequently, you are totally right, we need much more bigger space to conduct trial runs.


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Re: Tail rotor tune problem
« Reply #7 on: November 25, 2019, 10:39:17 am »
understood you have a motor at the tail.
you control the rpm via  esc.
but how to you control the esc?
manually via a nob on a rc transmitter or what?

great to see next video in a less heart breaking setting :)


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Re: Tail rotor tune problem
« Reply #8 on: November 25, 2019, 07:41:34 pm »
Hello again,

Tail rotor is connected to channel 4 in my TX, so it located in joystick which throttle located.

I tried and tried again I may have managed to solve the yaw rotation problem a little bit but other control settings are getting worse. Now it is creeping in the surface rather than flying. :(

I think I  need PID suggestion :/

Thx everyone


We followed a suggestion through this forum which is something like that
Integral shoud be twice as the proportional coefficient.

Video is ready! Agony of a heli

Tomorrow I will be trying this heli in the Basketball court. Keep you update with videos.

Thank you all guys.
« Last Edit: November 25, 2019, 09:42:26 pm by Aeronyx »

Re: Tail rotor tune problem
« Reply #9 on: November 26, 2019, 02:07:27 am »
Before I start, let me say that vibration can make the sensors go crazy.  I would attach USB cable to GCS, sit it on floor, and spin it up to try to take off while watching accel and gyro "scopes" in GCS.

If I make a guess, I guess that the roll/pitch PIDs in first video were too high and now they are too low.

Tail rotor should lock on and not drift at all.  If it is not, that usually happens either because trims are not centered or PIDs are too low.

Attitude looks mushy, not "locked on".  That usually happens because PIDs are too low.

I suggest you start with default PIDs, to get a good ratio between P, I, D.  If roll/pitch PIDs are too high, lower them by going to Stabilization page and dividing each of the 4 roll/pitch numbers in the Inner Loop section by say 2.  If too low, increase by multiplying each of the 4 numbers by 2.

Treat roll and pitch together as one set if it is "mushy" (too low) or "oscillating" (too high).

Do yaw separately.  If it does not "lock on" it is too low.  If it oscillates it is too high.

If you don't want to change the PID so much (2) you can use a number closer to 1, such as 1.5 when you multiply or divide.  Do not use 1.0 and do not use a number smaller than 1.0.

It is OK to do several changes of multiply or divide one after another.