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🏠Home🏠RC Main Discussion › Mechanical setup ... How to?
01-09-2021 04:10 PM  3 months ago
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Girard Ibanez

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Mechanical setup ... How to?
I'm try to understand my process and I apologize in advance for being a tickler or too technical/ meticulous in my mechanical setup(s).

Both occurrence on the Kraken 700 and 580. Applicable to other brands of helis.

1) All three servos arms at 90 deg to mainshaft. Servo 2 &3 servo arms verified with included alignment tool. Servo 1 arm using a straight edge ruler and 90 degree ruler.

2) All 3 linkage rod adjusted to swash plate with swash plate leveler in place.

3) Digital pitch gage referenced to top of electric motor and zeroed.

4) Blade feathered (aligned at balance point) then pitch linkage rod reconnected.

4) Swash plate resting firmly on swash leveler, pitch gage adjusted to read 0 degs.

Given the above, this portion of the setup ensures that the swashplate us leveled at 50% collective stick and the blade read 0 degs.

Now the issue ....

1) Flybarless gyro disabled.

2) At 50% collective stick Blade reads 0 degs. Good so far.

3) At 0% stick Blade reads -14.8 degs.

4) At 100% stick Blade reads 16.5 degs.

I can adjust the endpoints to dial in -12 / +12 degs.

Or

I can adjust for half the error (0.85 degs) by equally decreasing the length of all 3 linkage rods at the swashplate.

Now I have equal throw at 0% and 100% collective stick travel but the 0 degs Pitch at 50% stick shifted.

This has been mind boggling as I am trying to achieve a setup using mechanical adjustment verses electronic adjustments.

In summary I wouldn't feel the difference in flight but I am trying to understand how to approach this issue(s). Its all geometry and math do I know this puzzle can be solved mechanically.

Team Thunder Tiger
since 6/2005 to 12/2014
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01-10-2021 01:31 AM  3 months ago
Rojoalfa

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Very good job you did.

I would said that the main differences that explain your observations are:

Type of servos.
Transmitter/receiver brand.

For example, If you are working with futaba and change to spektrum, you would obtain different numbers.

Yes... Subtrims is the last thing to consider (I always said that Subtrims is for lazy people) but give us a great help.

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Saludos cordiales,
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01-10-2021 06:08 AM  3 months ago
Girard Ibanez

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I've setup Ikon2 / Spektrum and Neo / Vtouch.

Could never achieve equal throws at the end points.

With the Sab Kraken, the swash lever sets the swash at mechanical center. You don't even need the radio on. Adjust the pitch linkage rod for 0 degs. That half setup is done.

So the unequal pitch at Endpoints has to do with the software and servo centering.

Sure wish the programmers would allow a feature to have full travel symmetrical pitch.

Team Thunder Tiger
since 6/2005 to 12/2014
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02-06-2021 05:06 PM  67 days ago
hyflyr

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Baton Rouge, LA

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Mechanical setup ... How to?
I like this post in terms of the hunt for the cause in the differences at extremes. The missing piece of data is you didnt post the mechanical angle of each servo at the end points of travel. Based on the data posted it could be mechanical error or electronic. One would have to measure the angle of each servo at the extremes. I would guess as others posted the servos have different angular outputs at each end point. Not uncommon to require adjusting each servo's end points to acheive equal throw. More important to have the center at zero with all servo's at the same angle and rod lengths equal. That will greatly reduce the interactions between pitch changes and cyclic responses.
Scott
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02-07-2021 05:18 AM  66 days ago
Girard Ibanez

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hyflyr Mechanical setup ... How to?
I like this post in terms of the hunt for the cause in the differences at extremes. The missing piece of data is you didnt post the mechanical angle of each servo at the end points of travel. Based on the data posted it could be mechanical error or electronic. One would have to measure the angle of each servo at the extremes. I would guess as others posted the servos have different angular outputs at each end point. Not uncommon to require adjusting each servo's end points to acheive equal throw. More important to have the center at zero with all servo's at the same angle and rod lengths equal. That will greatly reduce the interactions between pitch changes and cyclic responses.
Measuring the angle is challenging. Not sure how one would accomplish such a task.

A reference can be established with:

1) the servo arm 90 to the servo body.

2) the servo arm 90 degree to the linkage.

3) the servo arm 90 degree to the frame which can be looked at as parallel / perpendicular to the main mast.

In today's setup manufacturers reference 90 degrees to the servo body. But then there's that error if the servo is not mounted or aligned so the servo is parallel to the frame.

Then there's different servo manufacturers that the servo output shaft causes cosign errors as it changes the linkage geometry.

In summary ... where do you begin to solve the riddle ... in a CAD drawing.

Team Thunder Tiger
since 6/2005 to 12/2014
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02-07-2021 12:45 PM  66 days ago
Peter Wales

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Orlando Fl

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Could your problem be as simple as the fact that there is an uneven number of teeth on the servo spline ands so if you have a servo arm at exactly 90 degrees and then rotate it 180 degrees, it will no longer be at 90 degrees.

So you cannot guarantee that all servo arms are at the correct position with no trim. Adding trim means that servo is now not in the exact center of its travel and so will not move equal distances either side of center
Peter Wales
http://scalehelicopters.org
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02-07-2021 05:05 PM  66 days ago
Girard Ibanez

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Peter Wales Could your problem be as simple as the fact that there is an uneven number of teeth on the servo spline ands so if you have a servo arm at exactly 90 degrees and then rotate it 180 degrees, it will no longer be at 90 degrees.

So you cannot guarantee that all servo arms are at the correct position with no trim. Adding trim means that servo is now not in the exact center of its travel and so will not move equal distances either side of center
I never considered this .... but it does makes sense. It would be nice if servo horn manufacturers made a 4 arm servo horn. The Futaba servo horns worked great back in the old days but wouldn't handle today's load.

Team Thunder Tiger
since 6/2005 to 12/2014
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02-08-2021 05:46 AM  65 days ago
hyflyr

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Baton Rouge, LA

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Well interesting you bring up servo horns. In the Futaba world they actually have labels on the back of their horns . It a tiny number/letter or on the older ones just a letter. So even though the servo horn looks identical they will line up at a slightly different position. This allows for getting the very exact position with no sub trim. Takes some trial and error to find just the right horn. Of course now the servo can just be programed to go where you want as well. But for the older gen servos you would need to have a decent stock of horns to find the set that is nuts on. It also takes a very long arm to see the real difference between 90 degrees and 89. A typical servo arm length may look 90 but really isn't.Scott
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02-08-2021 08:15 PM  65 days ago
Rojoalfa

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Punta de Mata, Monagas-Venezuela

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Servo horn... I don't recall exact number of theets that you have available to rotate but when you try to move just one Theet, it is more than 9 degrees...it is a lot!!!

Murphy's law said that the servo horn you choose is not the one, so no matter what you do to get a fine mechanical job, you finished the job with subtrims.

/
Saludos cordiales,
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02-25-2021 12:11 AM  49 days ago
EEngineer

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TX

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"Could your problem be as simple as the fact that there is an uneven number of teeth on the servo spline ands so if you have a servo arm at exactly 90 degrees and then rotate it 180 degrees, it will no longer be at 90 degrees."

Exactly.

One has to use subtrim to make all the arms "exactly" 90 deg. Unless you get lucky.

And then adjust the swash from there.
Logo 600SXs, 800XX, TDR IIs
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