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BrainDev
(@wp_8702697)
Member Admin
Joined: 3 years ago
Posts: 6
14/09/2020 11:54 am  

Your theory would be correct if when the model lands and the engine is turned off, the whole model rotates counterclockwise.
Only in this case would the tail rotor counteract the counterclockwise rotation.

However, in the video (and also from "Tail rotation rate" of the logs that go to positive values that correspond to a clockwise rotation) it is clearly visible that the model rotates clockwise and in this case the tail rotor cannot counteract this clockwise rotation but can only make it worse.

If the BLHeli firmware continues to rotate the tail rotor even when the control is removed, this is definitely the cause of the model's rotation in clockwise direction.


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Ian Contessa
(@ian-contessa)
Active Member Customer
Joined: 3 months ago
Posts: 12
14/09/2020 2:23 pm  

Hey.

 

Here is my flight log from a few minutes a go. I did a few take offs and landings to try and get some repetitive data on what the two channels, throttle and rudder, are doing at this point.

I'm currently thinking the main motor is shutting down faster than the tail, thus as it is creating thrust to counteract the torque reaction in the hovering state, on main motor shutdown it is still holding this right rudder input for a fraction of a second too long.

It makes me wonder if a throttle down delay would help and it is something I might try out. My throttle curve is also attached for refere

20200914 131202 resized 1
20200914 131211 resized 1

nce

 

Ian Contessa

 


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Ian Contessa
(@ian-contessa)
Active Member Customer
Joined: 3 months ago
Posts: 12
14/09/2020 6:58 pm  
Posted by: @wp_8702697

Your theory would be correct if when the model lands and the engine is turned off, the whole model rotates counterclockwise.
Only in this case would the tail rotor counteract the counterclockwise rotation.

However, in the video (and also from "Tail rotation rate" of the logs that go to positive values that correspond to a clockwise rotation) it is clearly visible that the model rotates clockwise and in this case the tail rotor cannot counteract this clockwise rotation but can only make it worse.

If the BLHeli firmware continues to rotate the tail rotor even when the control is removed, this is definitely the cause of the model's rotation in clockwise direction.

Evening Mate.

 

Correct the nose of the model follows the main rotor direction, so any right tail thrust would further enhance this problem. Which might be what is happening, it is difficult to tell how quickly the tail motor stops holding a heading as the throttle channel is lowered. My guess is it is a little behind it, thus it starts to puch the tail left (nose right) as the heading hold hangs for that short while. Then is maybe compounded further by the drag of the main motor, especially seeing as it's already moving nose right from the tail thrust.

 

Ah BLheli only keeps the tail motor idling for a second or two on shutdown, so very minimal right thrust and not enough to move the model as it's been sat on my work bench at the idle speed without swinging.

 

Ian Contessa


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BrainDev
(@wp_8702697)
Member Admin
Joined: 3 years ago
Posts: 6
14/09/2020 8:25 pm  
Posted by: @ian-contessa

Ah BLheli only keeps the tail motor idling for a second or two on shutdown, so very minimal right thrust and not enough to move the model as it's been sat on my work bench at the idle speed without swinging.

Two seconds is a very long time.

I am sure that the reduced rotation during those two seconds could not by itself make the model rotate.
However, the problem is that that small thrust is added to the magnetic drag of the main motor that carries the model. It is the sum of two small thrusts that can become a big thrust.


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Ian Contessa
(@ian-contessa)
Active Member Customer
Joined: 3 months ago
Posts: 12
14/09/2020 8:40 pm  
Posted by: @wp_8702697
Posted by: @ian-contessa

Ah BLheli only keeps the tail motor idling for a second or two on shutdown, so very minimal right thrust and not enough to move the model as it's been sat on my work bench at the idle speed without swinging.

Two seconds is a very long time.

I am sure that the reduced rotation during those two seconds could not by itself make the model rotate.
However, the problem is that that small thrust is added to the magnetic drag of the main motor that carries the model. It is the sum of two small thrusts that can become a big thrust.

Good Evening. 

 

Unfortunately in the video I was running the MULTI firmware and not the tail version and this one stops the tail straight away.

In the video you can see the tail rotor completely stop as it spins. The window in which it does and then the model spins is very small.

 

Ian Contessa 


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Ian Contessa
(@ian-contessa)
Active Member Customer
Joined: 3 months ago
Posts: 12
21/09/2020 2:47 pm  

Afternoon Guys.

 

Just to keep you updated, the piro on landing issue in the video is fixed. Bascially all I have done is swapped ESC's around so that the main motor now has a BLheli ESC with the MAIN firmware flashed to it and I done 3 landings on the pavement and the fuselage didn't even move. This is also running the BLheli TAIL firmware which keeps the tail motor at idle for a second or two after throttle shutdown.

My thoughts here at that even though I had turned off the braking on the previously installed BLheli_32 ESC, it must have still been applying some brake effect. As with the current setup the main rotors do take longer to slow down than before.

 

At least now I can deal with the tuning.

 

Ian Contessa


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