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How to achieve stable hover?

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(@calvinliang11361)
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So the MSH instructions are to make absolutely sure the swashplate is level in check mode. I've tried that using the ziptie method and gotten the swash level to what must be within microns, but I'm finding that there's a persistent slight drift to the left. And before anyone asks no there are no trims or subtrims applied in my transmitter. What I think the problem is this FBL discharges integral constantly(basically constantly purging its awareness of what the target attitude is), so any forces that act to push the heli off its axis will eventually have an effect, that includes the thrust produced by the tail rotor. This is not an issue at all with say OMP M1/M2 where integral is only discharged upon motor shut off, so if I put the heli in a right lean to counteract thrust from tail rotor and put it in a hover, it keeps itself in that attitude until I command otherwise. What some people have suggested is to put a slight right lean to the swashplate, but doesn't this contradict manufacturer instructions? What does MSH say about this? What's the proper fix?


   
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(@customercare)
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We are not aware that we have written that the swashplate ABSOLUTELY needs to be leveled.
Can you tell us where you read this so that we can correct any inaccuracies and possible misunderstandings?

Flybarless flight controllers, emulate the operation of flybarred models and the swasplate should be adjusted exactly as it was (and still is) done with flybarred models:

1) During model assembly and initial setup, it is "convenient" that the swashpalte to be level so that the maximum and minimum collective and cyclic pitch tilts can be adjusted by reading the same degree values equally on any of the blades.

2) Later, at the airfield, when you make the first test flights of the model if the model has a tendency in hover to always go in the same direction, then you will correct the length of the links that go from the servos to the swasplate to tilt the swasplate to counteract the tendency to always go in the same direction. In hovering, RC heli (with or without flybars) will never stay stationary in position (RC heli are inherently unstable) but will tend to tilt and shift. The important thing is that they tilt in different directions each time and never in the same direction.

What is critical, however, is the proper balancing of the model so that when lifted by means of two fingers placed under the main blade bolts it should have the main shaft perfectly perpendicular to the ground.


   
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(@calvinliang11361)
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Joined: 2 years ago
Posts: 23
Topic starter  

Okay you didn't say it has to be "absolutely" level and maybe only drilled into my head that it does by many people. But I didn't see in any MSH documentation instructing users to trim the swashplate to counteract drift either. But wouldn't that not be the best idea anyway? For example I need a slight right lean to counteract tail rotor thrust in upright hover, so I mechanically trim the swashplate to tilt to the right a bit, giving the heli an inherent tendency to roll right. Now I want to hover inverted, which now needs a slight left lean to counteract the tail rotor thrust that is now directed towards the left, so now I'm having to fight inherent right rolling tendency I've introduced into the model earlier for upright hover. 


   
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(@customercare)
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Posted by: @calvinliang11361

....But wouldn't that not be the best idea anyway? ....

Not so.
When models hover they have a tendency to tilt slightly in a direction that can change due to the thrust of the tail rotor, which is not not on axis with the main rotor but is positioned below the main rotor. The direction of the tilt can change depending on the direction of rotation of the main rotor.
This slight tilt of the main shaft is compensated for by tilting the swashplate to a position more parallel to the ground rather than perpendicular to the main shaft.
When the model is in inverted flight, the tilt caused by the thrust of the tail rotor that is above the main rotor causes the main shaft to tilt in the opposite direction, and the swashplate will, however, continue to be tilted to a position more parallel to the ground rather than perpendicular to the main shaft.

 


   
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(@calvinliang11361)
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Topic starter  

Well what if it's an elevated tail rotor? What can be done then?


   
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(@customercare)
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If you are referring to a reproduction/scale in which the tail rotor is placed above the main rotor nothing changes they just have to be thought of in the opposite way.


   
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(@calvinliang11361)
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Joined: 2 years ago
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Topic starter  

But for sure something changes. Let's say the tail rotor isn't underneath nor above the main rotor, but in line with the main rotor, rather than let tail thrust push the main shaft into a tilt, you're now relying completely on the swashplate to put it in that tilt. With a clockwise spinning main rotor for example. With a level swash, in upright hover, if I put it in a right tilt to counteract tail rotor that is producing right thrust, with decaying I term(key point), gravity acting on the fuselage is going to eventually pull the heli back towards level and the right thrust from tail rotor is then again pushing the heli towards the left resulting in left drift. If I trim the swashplate right to give the heli a right rolling tendency to counteract this phenomenon, then the heli stays in that right tilt in upright hover for the most part. Now I flip the heli to hover inverted. Tail rotor is now producing left thrust, which means I need to tilt the heli left, a process that is now being undermined by the right rolling tendency.


   
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(@customercare)
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Joined: 6 years ago
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It is not clear what you want.
Does your model have the tail rotor at the height of the main rotor?
We have given you the solution to the drift problem of 99% of models like yours.
(Assuming, of course, that the flight controller configuration was done correctly as explained in the instructions).
Of course you are free to dispute what we have suggested, not to follow our advice, and you are free to do what you want.
If you are convinced that the problem is the decay that ALL of the most well-known flybarless controllers for RC heli that emulate the operation of a mechanical flybar have, we suggest that you instead use one of the many flight controllers designed and born for quadricopters and adaptable also to RC heli to fly them not as RC heli but as quadricopters. That is if you are certain and sure of how they work.
However, we believe it is pointless to continue the discussion here as well since on HeliFreak you are repeating the same things and the posts written by you and other users have already reached 20.


   
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(@calvinliang11361)
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Joined: 2 years ago
Posts: 23
Topic starter  

I wasn't aware MSH representatives would be communicating through helifreak and thought I might get some more insight through an official channel.

Anyways I guess I'll get to my point. Is there a way to configure the FBL such that it retains integral in flight and discharge it for example at spool up/down or at zero collective? If there's not already a way to do this would you consider implementing a method? This would make things like CG, translating tendency, tail drag compensation etc less of a consideration I'm sure.

I know there are other FBLs that do this but my resources are limited and I really would rather not invest in another system.

Sorry if I've given you a hard time. It wasnt my attention at all and I'm aware that my take on things and requests can be a bit unique and nitpicky 

Thank you for your time and consideration. 


   
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(@customercare)
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Posted by: @calvinliang11361
Is there a way to configure the FBL such that it retains integral in flight and discharge it for example at spool up/down or at zero collective? If there's not already a way to do this would you consider implementing a method?

The two answer are no, no.

As already explained, we repeat:
When following decay the servos return to their zero position and no further rotation read by the gyroscopes or commands sent by the transmitter is generated, the model must be mechanically tuned not to have tendencies to always translate in the same direction in the absence of wind. This is achieved by adjusting the links from the servos to the swashplate to compensate not only for tail rotor thrust but also for interactions caused by main blade air pushed toward the canopy, toward the skids, toward the muffler (in internal combustion models), toward the tail boom, toward the tail rotor, and at the opposite end the tail rotor air pushed toward the main rotor and all the resulting turbulence and also to compensate for deviations of the center of gravity not only in the longitudinal axis but also in the latitudinal axis.

Posted by: @calvinliang11361
I know there are other FBLs that do this
How can you be sure? Have you analyzed the firmware code used by these flight controllers you are talking about?

 

 


   
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