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Ian Contessa
(@ian-contessa)
Active Member Customer
Joined: 8 months ago
Posts: 13
Topic starter  

Evening All.

Hope you're all safe and well?

I'm messing around converting an OMP M2 to use seperate FBL and ESC's, I will post some photos of the setup when I can as I am trying to keep it all neat and tidy. Initially I started out with a uSpirit and while it took me ages to get it flying, the manual stated base parameters don't work it seems (at least not on this model) so while it is now hovering aorund, the cyclic induces a small boom wobble on quick stab elevator inputs that so far I am now able to remove.

So I've purchased a uBrain and am in the process of setting it up on the bench, I must say I am impressed with the amount of parameters I have available to me to tune, so I am looking foward to this. Iv'e also wired in the OpenTX Integration with a Jumper R1F receiver to my TX16S transmitter which gives me a lot of things to play with when I have this flying.

However I have hit a hurdle with the tail ESC/motor setup and wondered if you could help please?

While I have it working ok, when I get to the step whereby I hold in left tail command and then hit the - button in the software until the tail motor starts, it then will not stop. If I have this value set to where the tail does stop, either on closed throttle or TH, if I give even a small amount of left stick the tail stops which I am under the impression it shouldn't.

Have a missed a parameter or step here that is giving me this hurdle?

Thanks for your time.

Ian Contessa


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Ian Contessa
(@ian-contessa)
Active Member Customer
Joined: 8 months ago
Posts: 13
Topic starter  

Here it is flying in the back garden

 

https://www.youtube.com/watch?v=W7UjIuBDCLc


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BrainDev
(@rik)
Member Admin
Joined: 3 years ago
Posts: 3
 

Good morning,
We do not know your OMP M2 model.
The default values that are set when you select the "Tail Motor driven" icon for the tail in Wizard panel 7 "Servo Setup (Output)" are the values we tested, tested and found to be optimal values for the most popular tail motor control ESC models (Blade models).

If your model (which we do not know) uses a different ESC for tail motor control, you may need to change these values.
To do so just go to the ADVANCED section, tab "Common", parameters "Servos" and adjust the three values of the Servo4 (the output controlling the tail) to change the Minimum, Middle and Maximum value.
We hope we have been of help.


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BrainDev
(@rik)
Member Admin
Joined: 3 years ago
Posts: 3
 

We have seen the video
Nice flight!
From the video we don't seem to see any particular problems (except the final rotation at landing), but the feeling of the pilot cannot be perceived by a video.


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Ian Contessa
(@ian-contessa)
Active Member Customer
Joined: 8 months ago
Posts: 13
Topic starter  
Posted by: @rik

Good morning,
We do not know your OMP M2 model.
The default values that are set when you select the "Tail Motor driven" icon for the tail in Wizard panel 7 "Servo Setup (Output)" are the values we tested, tested and found to be optimal values for the most popular tail motor control ESC models (Blade models).

If your model (which we do not know) uses a different ESC for tail motor control, you may need to change these values.
To do so just go to the ADVANCED section, tab "Common", parameters "Servos" and adjust the three values of the Servo4 (the output controlling the tail) to change the Minimum, Middle and Maximum value.
We hope we have been of help.

Good Morning.

 

Thank you for your quick response, it is appreciated.

Yeah this little model is very nice and out the box flies well, but things can always be improved and a more mature FBL system is something it will gain from I feel.

This flight is only simply moving around within the contstraints of the back garden for now and gaining more confidence in the setup. Once I venture out to a bigger field it will be more intersting.

 

Thank you for this idea, but this is where I am experiencing the problem if you can call it that, as ultimately the model is flying very nicely and locked in.

As per the manual I adjust the tail channel sliders to achieve full power for right tail input and then check that with full left rudder stick applied the is motor off. This I have verified and go onto the next step, which is to adjust using the - in this case until the motor just starts and then add 3 more clicks to be sure, this sets the lowest speed of the tail motor for full left rudder so that it doesn't stop in flight.

At this point though the tail motor then stays on and will not switch off with either the low throttle stick or throttle hold position, it does if I leave the full left rudder slider where the motor is off and not running slowly as requested in the manual. I am assuming that the tail would remember the motor off value and then the full left rudder motor idle value as two seperate points, using the off value for low throttle & throttle hold and the left rudder idle speed for full left rudder channel input.

So I am wondering now, going by what you've mentioned, is the channels middle value critical here to set the left rudder idle speed where the tail motor will not completely stop on full left rudder and that the other left control slider is to set the actual stop point in the travel range?

Or is it that in flight full left tail rotor input would not stop the tail at all, so I just need to see it stop on the bench in front of me?

 

I am using an FVT Little Bee 30 amp ESC on the tail flashed with BLheli MULTI currently, as BLheli TAIL firmware keeps the tail motor spinning for a few more seconds after shutdown.

 

Thanks for your time and chat soon.

 

Ian Contessa

 

 

 


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andreas.fassl
(@andreas-fassl)
Active Member Customer
Joined: 2 years ago
Posts: 17
 
Posted by: @rik

Good morning,
We do not know your OMP M2 model.
The default values that are set when you select the "Tail Motor driven" icon for the tail in Wizard panel 7 "Servo Setup (Output)" are the values we tested, tested and found to be optimal values for the most popular tail motor control ESC models (Blade models).

 

Here I'd like to add something, based on my experience.

Correct the settings have been developped and tested with Blade ESC. When you use TH to stop main motor, the agreement was to stop tail motor as well.

 

The little big difference we face with all new ESC and direct drive helis is the rotor head speed.

OMP has almost double the speed on the Rotorhead compared to the 130S / 150S  !!!

 

Here I kindly ask, if you can change in the firmware, that tail signal is cut with a delay of 1-2sec (NOT MORE) which should be then sufficient, that main torque is not that huge anymore to make the heli to do some piruettes.

Will be great if this (minor) change can be realized in one of the upcoming firmware releases, then the effect like Ian demonstrated should not be an issue anymore.

Just for confirmation, I would be happy too about this 1-2sec more on tail control  😉

 


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BrainDev
(@customercare)
Member Admin
Joined: 3 years ago
Posts: 546
 
Posted by: @andreas-fassl

......

Here I kindly ask, if you can change in the firmware, that tail signal is cut with a delay of 1-2sec (NOT MOE) which should be sufficient, that main torque is not that huge anymore to make the heli to do some piruettes.

Will be great if this (minor) change can be realized in one of the upcoming firmware releases, then the effect like Ian demonstrated should not be an issue anymore.

Just for confirmation, I would be happy too about this 1-2sec more on tail control  😉

 

The counter-torque is generated by the thrust of the motor. when throttle hold (or throttle cut) is turned off the motor and the counter-torque goes immediately to zero even if the blades are still rotating fast thanks to the unidirectional bearing.
In the movie, at the end of the flight after landing the model rotates clockwise, as if the tail rotor gave maximum thrust or as if the main rotor dragged the entire model together.
It would be useful to have the flight log of that flight to understand if when the throttle goes to zero, the tail engine control is turned off and does not go to maximum. In that case, the tail throttle should be turned off before and in advance and not after.

Maybe the OMP M2 model has no unidirectional bearing between the main shaft and the motor?


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andreas.fassl
(@andreas-fassl)
Active Member Customer
Joined: 2 years ago
Posts: 17
 

On the video you can see - hardly but for sure - that tail rotor stops with no delay. checked once more th vid 4:17, main rotor is still on speed

OMP M2 is a direct drive heli, so your assessment (option 2) is the most likely version "as if the main rotor dragged the entire model together".

I will do some test flight and will send you the log with dedicated tail parameters.

@Ian - will be good if you can do same flight with logs acivated

 

grafik

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Ian Contessa
(@ian-contessa)
Active Member Customer
Joined: 8 months ago
Posts: 13
Topic starter  
Posted by: @customercare
Posted by: @andreas-fassl

......

Here I kindly ask, if you can change in the firmware, that tail signal is cut with a delay of 1-2sec (NOT MOE) which should be sufficient, that main torque is not that huge anymore to make the heli to do some piruettes.

Will be great if this (minor) change can be realized in one of the upcoming firmware releases, then the effect like Ian demonstrated should not be an issue anymore.

Just for confirmation, I would be happy too about this 1-2sec more on tail control  😉

 

The counter-torque is generated by the thrust of the motor. when throttle hold (or throttle cut) is turned off the motor and the counter-torque goes immediately to zero even if the blades are still rotating fast thanks to the unidirectional bearing.
In the movie, at the end of the flight after landing the model rotates clockwise, as if the tail rotor gave maximum thrust or as if the main rotor dragged the entire model together.
It would be useful to have the flight log of that flight to understand if when the throttle goes to zero, the tail engine control is turned off and does not go to maximum. In that case, the tail throttle should be turned off before and in advance and not after.

Maybe the OMP M2 model has no unidirectional bearing between the main shaft and the motor?

Evening Mate.

 

Yes you are correct, it seems it is the tail rotor's thrust still acting on the model, or in this case I think is still counteracting the torque reaction on the fuselage. The latter as I remove the torque loading on the models fuselage by reducing the main rotor RPM, takes a second or so to catchup and so the tail spins.

 

As you've guessed the OMP M2 does not have a one-way bearing on the mainshaft as it is a direct drive setup, with the motor bell mounted directly to the main shaft in the same configuration as on the Goblin Fireball. So as you say ideally the tail motor maybe still needs to be in control for a few seconds on main motor shutdown, so the tail is still in control to counteract any torque swing on the fuselage.

 

I wonder if maybe some form of difference between a normal throttel stick down main motor shutdown Vs a throttle hold state shitdown, sort of like the Castle Creations bailout where you have one throttle position saved for motor off and another for motor off, but get ready to spool back up faster if you see the throttle signal advance. But in the tail motor model case, keep the tail gyro alive for a second or two during a normal spool-down to stop any tail swings. 

In my case it didn't help that I was on a smooth floor with carbon fibre skids and no rubber grip to stop the model rotating. Plus the main motor is not running an ESC with a smoother throttle response as I cannot flash the BLheli MAIN firmware to it to invoke a slow spoolup and possibly a much smoother slow-down, that is my next task to swap ESC's around.

 

I will see if I can pull the log off, but it might be of the quick flight i made today though.

Just to add, I have flashed BLheli TAIL firmware to my ESC today for a test. This firmware does keep the tail idling for a few seconds after shutting down, but no gyro compensation is working at this time as the throttle signal is at the low point. So maybe a simple delay would help.

Ian Contessa


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andreas.fassl
(@andreas-fassl)
Active Member Customer
Joined: 2 years ago
Posts: 17
 

I will do flight with this log setting, please advise if you need something else

grafik

Did the test with only 2200RPM (2187 as per log), and you can see, that there is a 26deg/sec peak the moment you cut throttle. Will do more test with higher RPM.

@Ian will be good if you can do same log with your current setup

grafik

 


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BrainDev
(@wp_8702697)
Member Admin
Joined: 3 years ago
Posts: 6
 

All correct Andreas.
That's what was needed.
The tail rotor stops correctly before the main engine stops.
It doesn't get any better than that.

On models with the tail motor, the tail propeller can only push to rotate the tail to the left (clockwise seen from above) or stop and not push by letting the tail rotate to the right (counterclockwise seen from above) thanks to the counter torque generated by the main rotor.
The graph shows that the tail propeller has been stopped and therefore no longer pushes to the left but the tail rotates the same to the left due to the attraction of magnets on the engine case towards the stator masses.
The only way to avoid this would be to use a one way bearing on the crankshaft and/or main shaft.
Or the tail propeller could push to the right.
But to do this would require both reversing the direction of rotation of the motor and reversing the pitch of the tail propeller blades and this is not possible.

The only thing that could still be evaluated when reading the tail propeller rpm is whether when the tail signal goes to zero, the propeller stops immediately and stops pushing or continues to rotate and push by inertia. If this is the case, it is necessary to bring the tail control to zero some time in advance so that when the main engine starts to drop the tail propeller is already perfectly stopped and no longer gives the slightest thrust to the left. Or you would need to activate the engine brake in the ESC of the tail engine so that when the tail control goes zero, the tail propeller stops immediately.


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andreas.fassl
(@andreas-fassl)
Active Member Customer
Joined: 2 years ago
Posts: 17
 

Can we agree to talk same - what you describe in last pargraph doesnot make any sense. Your propsal will make it even worse.

Correct will be to keep tail motor control active to the moment main motor RPM is below a certain threshhold - to be defined.

I made some more test and the critical period is less than 100ms after the signal TC is received.


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BrainDev
(@wp_8702697)
Member Admin
Joined: 3 years ago
Posts: 6
 

As for the OMP M2 model, please confirm that:

immagine

1) Can the tail motor rotate in one direction only?
Yes/No?

2) The tail blades are pre-printed and therefore have a fixed shape and inclination that cannot be modified?
Yes/No?

3) According to 1 & 2 above the tail rotor can only push the tail only to the left (tail seen from behind)?
Yes/No?

4) According to point 3 above can the tail rotor NOT pull the tail to the right in any way?
Yes/No?

5) If the model tends to rotate to the left after landing and removing throttle from the main rotor, can the tail rotor according to point 4 above in no way counteract the rotation of the model to the left?
Yes/No?

6) Based on all the above, if the tail rotor were to turn even very little, would it only cause a worsening of the left rotation and not counteract it?
Yes/No?

7) Is it better to stop the tail rotor completely instead of continuing to rotate it?
Yes/No?

8) The sooner you stop the (even minimal) thrust of the tail rotor to the left, the better to reduce the tendency of the model to turn left?
Yes/No?


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andreas.fassl
(@andreas-fassl)
Active Member Customer
Joined: 2 years ago
Posts: 17
 
Posted by: @wp_8702697

As for the OMP M2 model, please confirm that:

immagine

1) Can the tail motor rotate in one direction only?
Yes/No? YES

2) The tail blades are pre-printed and therefore have a fixed shape and inclination that cannot be modified?
Yes/No? CORRECT, fixed shape

3) According to 1 & 2 above the tail rotor can only push the tail only to the left (tail seen from behind)?
Yes/No? YEP, BUUUT, the tail runs with certain RPM, to balance torque of Main motor - lets call ist for our case 40% of possible tail RPM keeps the heli balanced.

4) According to point 3 above can the tail rotor NOT pull the tail to the right in any way?
Yes/No? - As per 3) above, less than 40% of tail RPM will use main mortor tourque to make heli roate to the right.

5) If the model tends to rotate to the left after landing and removing throttle from the main rotor, can the tail rotor according to point 4 above in no way counteract the rotation of the model to the left?
Yes/No? - This si just as there is no counter torque.

6) Based on all the above, if the tail rotor were to turn even very little, would it only cause a worsening of the left rotation and not counteract it?
Yes/No? NO

7) Is it better to stop the tail rotor completely instead of continuing to rotate it?
Yes/No? NO

8) The sooner you stop the (even minimal) thrust of the tail rotor to the left, the better to reduce the tendency of the model to turn left?
Yes/No? NO

The discussion and proper operation of motor tail is even reflected in the BLHeli Firmware (2015) where there is dedicated Tail firmware will stop motor 1-2 sec after main motor.

 

I produces same momentum during flight (diagram attached) , and tail motor was perfectly able to compensate this tourqe.
At ThrottleCut at the end - you can see there is no counter movement possible to balnce out due to "stopped" tail motor.

To be fair - If you reduce throttle by hand towards 0 by RX - the effect is not visible at all! It is about some miliseconds.....
My assessment to keep 250ms TailOut is also not correct, but some 20-50ms will be suffiient to reduce the impuls responsible for this crazy rotations.

So what Ian demonstrated in the video it is directly linked to the Throttle Cut, and the situation that tail motor is stopped earlier than main motor. There is no other situation in flight, where this can happen - beside the tail motor fails.

grafik

 

There is no error in the firmware for tail motor, all is good!

There was simply the enhancement request to keep TailOut active for this "to be defined" time on throttleCut.

In my case I can confirm that already 20ms will be perfect.

If there is no chance to implement in Firmware, I recommend users with this effect to have one dedicated throtlle curve to start/stop the motors.

 

 


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Ian Contessa
(@ian-contessa)
Active Member Customer
Joined: 8 months ago
Posts: 13
Topic starter  
Posted by: @wp_8702697

As for the OMP M2 model, please confirm that:

immagine

1) Can the tail motor rotate in one direction only?
Yes/No?

2) The tail blades are pre-printed and therefore have a fixed shape and inclination that cannot be modified?
Yes/No?

3) According to 1 & 2 above the tail rotor can only push the tail only to the left (tail seen from behind)?
Yes/No?

4) According to point 3 above can the tail rotor NOT pull the tail to the right in any way?
Yes/No?

5) If the model tends to rotate to the left after landing and removing throttle from the main rotor, can the tail rotor according to point 4 above in no way counteract the rotation of the model to the left?
Yes/No?

6) Based on all the above, if the tail rotor were to turn even very little, would it only cause a worsening of the left rotation and not counteract it?
Yes/No?

7) Is it better to stop the tail rotor completely instead of continuing to rotate it?
Yes/No?

8) The sooner you stop the (even minimal) thrust of the tail rotor to the left, the better to reduce the tendency of the model to turn left?
Yes/No?

Hey Buddy.

 

1. Correct, one direction only. Speed up for right yaw and slow down for left yaw done so via torque reaction.

 

2. Correct yes, tails blades are molded and of fixed pitch and cannot be changed in any way. Unless physically modified with a file or other.

 

3. Yes correct, thrust increases to push the tail left (nose right)

 

4. Correct, left yaw is achieved by slowing of the tail rotor only and letting the torque reaction put the nose left.

 

5. No it cannot, unless the slowing of the tail rotor can control/stop the models fuselage from rotating nose left.

 

6. Are we talking nose left or tail rotor left when viewed from the back? Essentially I think the problem with the M2 is that because it is a direct drive main rotor connected directly to the motor and as you have already said, the magnetic drag of the main motor then takes the models fuselage with it as it slows down. Whereas a normal model would tend to spin the fuselage in the opposite direction to the rotors, this model takes it with it instead.

 

7. Good question, as without reversing the tail rotor direction I don't think simply slowing it down will have any affect on trying to stop the main rotor rpm dragging the models fuselage around with it. However there might be something to consider with the tail rotor slowly spinning to act as a drag chute if you like and simply place a paddle like device at the rear to apply aerodynamic drag to help stop the models fuselage being dragged round with the main rotor.

 

8. Potentially yes, as if the main rotor RPM drops a few thousands of a second before the tail rotor thrust drops away, then this will already start the models fuselage turning nose right, which is then picked up and taken further by the drag from the motor/rotor disk.

 

Essentially fitting a one-way bearing on the bottom of the main shaft will alleviate a lot of this problem, as it would allow the motor to stop pretty quickly but the main rotor to slowly drop in rpm without effecting the fuselage. Also maybe not allowing the main motor ESC to simply drop to zero quickly, but slowly ramping it down in RPM would help and then keeping the tail motor with gyro assist working for a few seconds would also help.

But then for safety perhaps you'd want to maybe have two shutdown options;

 

1. The normal fast switch off of the main and tail ESC, activated by throttle hold maybe.

2. A delayed power down of both ESC's to allow the main rotor RPM to drop slowly and while doing so the tail rotor to still control any effects on the tail.

 

These options could be invoked by the throttle position, a bit like Castle Creations bailout throttle settings.

 

I appreciate your input on this.

 

Ian Contessa


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