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Sab Goblin 280 Fireball swash type?

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calvinliang11361
(@calvinliang11361)
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This model has a somewhat irregular swashplate. I cannot find any information online about what swash type the choose for this particular model. 120 seems to work better than either 135 or 140 but I still see the swivel bearing bob up and down a bit on the mainshaft when I stir the cyclic. With the blades on, folded and lined up with zero collective, they drift apart as I play with the cyclic and tilt the swashplate in any direction. Is this fixable?


   
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BrainDev
(@customercare)
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If you cannot find information about your model's swashplate in the model documentation (manual, manufacturer's website, dedicated forums), we suggest that you contact SAB support and ask about how the flight controllers should be programmed relative to the swashplate.

We remind you that in the ADVANCED section, "Common" tab, CCPM, you can modify the CCPM mixer configuration by changing (if necessary) the swashplate angles.


   
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calvinliang11361
(@calvinliang11361)
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So I tried playing with the servo angles and here's what I noticed. With the angles at default values for 120, if I rock the swashplate side to side or fore and aft, I see the swivel ball get pulled down on either end of the tilt, but it gets pulled down evenly. If I adjust the angles of servo 1 and 3 so that the blades stay lined up on one end of the tilt, they drift apart even further on the other end of the tilt. So if i change those servo angles the swivle ball stays put better when I for example pull cyclic back but when I push cyclic forward the swivel ball gets pulled down further than before. The default  values for 120 seem to give the most balanced behavior.


   
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BrainDev
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The angle of the swashplate attachment points has nothing to do with asymmetry problems (negative movements different from positive movements).

The asymmetry problem occurs solely and only when in the center position (zero pitch) all three servo horns are not perfectly perpendicular (at exactly 90°) to the main shaft.

There is a Check Mode function for this adjustment, which is automatically activated when you go into panels 8 and 9 of the Wizard or via the appropriate checkbox in the CCPM section in ADVANCED.

Even if the pitch stick is not perfectly centered this function generates a high deadband that keeps the output signal centered at zero (= 1520uS).

If in Check mode with the pitch stick at the center the servo horns are too far away from this 90° position it may be necessary to remove the retaining screw slide the horns out and reinsert them into the servo spline at a more central position.

The + and - buttons in panel 8 of the Wizard are not for aligning the swashplate at all and should not be used for that at all but are used to make the small corrections to be able to bring the servo horns exactly to 90° with respect to the main shaft.

Then you align the Swashplate by lengthening or shortening the links that go from the servos to the Swashplate.

This is all because the movement of the servo horns to move the links is not linear but rotary, and the movement generated toward the links is greater with the horns in the center and decreases as the horns go up or down.


   
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calvinliang11361
(@calvinliang11361)
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Topic starter  

The servo horns are indeed all perpendicular to the mainshaft. Servo links aren't adjustable but the pitch links are. I installed the servo horns as perpendicular as possible in check mode before touching anything else on that panel, then I made the necessary corrections through the software to bring them perfectly perpendicular, checked that the swashplate is level, and then zeroed the pitch through the pitch links. I'm not sure that there is any asymmetry in the up and down movements. The swashplate stays perfectly level from fully collective down to collective up, and the pitch at full negative collective matches perfectly with full positive collective. I've attached pictures of the setup with all the servos at neutral as well as a video highlighting the phenomenon I've been describing.

20220805 154250
20220805 154341
20220805 154236
20220805 154544

   
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BrainDev
(@customercare)
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Have you contacted SAB support?


   
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calvinliang11361
(@calvinliang11361)
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Topic starter  

@customercare yes I did. They said 120 is the right configuration and to ask you guys about it.


   
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BrainDev
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Since in twelve years and hundreds of thousands of units used by users configured for 120-degree swashplate no one has ever had a problem, the problem is not with the flight controller but mechanical (or in the servo travel). Either it is a mechanical problem with all Goblin 280s or it is a problem with your specific model. Have you looked in the international forums (EG: HeliFreak) if other users with Goblin 280s report the same problem as your?
Anyway, if you want, you can send as an attachment to a post the configuration file of your FCU so that it can be analyzed if by any chance any paramenters have been misconfigured.


   
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calvinliang11361
(@calvinliang11361)
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Topic starter  

No one has any comment on this since the week I've posted about this observation on helifreak. Here is my config file:

Also if it helps here's a diagram of the servo layout from the build manual: 

Screenshot 20220806 215142 Adobe Acrobat

   
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calvinliang11361
(@calvinliang11361)
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Topic starter  

Soooo any insights?


   
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Jimmy
(@jimm-y)
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@calvinliang11361 

Could it be your pitch, looks out of range.

Untitledb

 


   
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Jimmy
(@jimm-y)
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Posted by: @calvinliang11361

The servo horns are indeed all perpendicular to the mainshaft. Servo links aren't adjustable but the pitch links are. I installed the servo horns as perpendicular as possible in check mode before touching anything else on that panel, then I made the necessary corrections through the software to bring them perfectly perpendicular, checked that the swashplate is level, and then zeroed the pitch through the pitch links. I'm not sure that there is any asymmetry in the up and down movements. The swashplate stays perfectly level from fully collective down to collective up, and the pitch at full negative collective matches perfectly with full positive collective. I've attached pictures of the setup with all the servos at neutral as well as a video highlighting the phenomenon I've been describing.

Not sure what your wanting to proof here but nowt do with FC setup or mechanical setup other than a guide we sometimes use to check zero pitch @ mid stick, what you appear to be doing is using the elevator stick to push pull the blades, I've not seen this in any heli manual setup before, so I would say I would expect that happen.

Edit" if you swing blades round the other way (not the rotor) I bet it would do the same.


   
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calvinliang11361
(@calvinliang11361)
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Joined: 4 months ago
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Topic starter  

@jimm-y I'm only manipulating the cyclic but as you can see the blades are changing pitch relative to each other indicated by them drifting apart when I tilt the swashplate, as if I'm also giving some collective input.


   
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Jimmy
(@jimm-y)
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Posted by: @calvinliang11361

@jimm-y I'm only manipulating the cyclic but as you can see the blades are changing pitch relative to each other indicated by them drifting apart when I tilt the swashplate, as if I'm also giving some collective input.

Don't quite get it seems meaningless to me, I would just keep with the manuals mechanical setup and the Brain configurator.


   
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BrainDev
(@customercare)
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In the configuration file you posted we didn't notice any serious problems.

It is also not clear to us what kind of test you are doing in the video and what you want to see and achieve with one blade pushing down strongly on the link going to the swashplate and the other blade pulling up strongly on the link going to the swashplate. All model components (swashplate, uniballs, etc.) have plays and tolerances that are never totally zeroable.

Moreover, from the video you can see that the blades rotate and move from the center position (tail rotor rotates) and it is normal that if the blades move while giving elevator command the relative heights of the blades change.

In addition to this, it is very difficult to be able to give with the cyclic stick solely and only elevator command without the stick moving minimally by aileron.

This is a type of test we have never seen done before to check cyclic/collective interactions and it really makes little sense.

It should still be done with the check mode on to rule out any gyro intervention caused by the inevitable movements of the model on the plastic skids that flex as the blades move.

To check that the cyclic controls do not interact with the collective pitch one would instead and much more simply have to check that the center ball of the swashplate does not rise or fall along the main shaft while moving the cyclic stick.


   
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