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Old 03-05-2010, 02:35 AM   #1
popadel
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Default Rudder sub trim Q

With every set up I have always had 0 trim on the rudder servo and a perfect hover in rate mode.
I am working on a 3G Trex 700 project that requires some modification and the only way to get full rudder movement left and right is to use a bit of sub trim. Its space limitation as i moved the BLS 251 into a confined space. Ruder servo horn is as close as i can get it and does not line up as i want it.

How bad is it to have 5-10 points sub trim in the tail servo? Will it affect my flight characteristics? This is a 5-6Kw heli with -+15 deg pitch and 710 blades so its destined for some serious acrobatics and accurate control.

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Old 03-05-2010, 03:22 AM   #2
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Its a continious debate. I also followed your method but after listening to Finless and setting up 3 Align GP750's I have since done the subtrim route.
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Old 03-05-2010, 07:24 AM   #3
ACKopter
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I always thought it was OK to use subtrim on the rudder, My personal experience with the Align GP750 gyro proved otherwise. I had constant drift in a hover and servo creep on the bench, once the subtrim was removed all problems went away.
FWIW this was on a stock Trex500ESP using all stock electronics and motor/ESC. Tail servo was the align ds520.
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Old 03-05-2010, 08:27 AM   #4
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as long as you rebind after getting everything set up AFAIK the gyro will use that as the new center point
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Old 03-05-2010, 08:48 PM   #5
ACKopter
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Quote:
Originally Posted by superjoe83 View Post
as long as you rebind after getting everything set up AFAIK the gyro will use that as the new center point

Interesting, I really cant recall whether or not I did re-bind after my set-up. I used the subtrim as a result of being lazy and the bench creep forced me to set up my mechanical better so I'm better off in the long run anyway.
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Old 03-06-2010, 06:35 AM   #6
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A lot depends on the gyro you are using.

Some are fine with subtrim. Some are not. Some require subtrim.
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Old 03-06-2010, 07:55 AM   #7
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you don't need to rebind, and subtrim is ok to use
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Old 03-06-2010, 08:04 AM   #8
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Quote:
Originally Posted by Pinecone View Post
A lot depends on the gyro you are using.

Some are fine with subtrim. Some are not. Some require subtrim.
One example of one that is not fine with subtrim is the Spartan DS760 with 1.x firmware. A buddy had problems getting his gyro to initialize and we discovered he had enough subtrim added that the initialization inhibit was kicking in (a feature intended to cope with Spektrum receiver link delay times). The 2.x firmware doesn't have that problem because Spartan removed the feature and went with alternate methods.
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Old 03-06-2010, 10:49 AM   #9
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The OP was refferring to the 3G and I belive it is the same as the 780 gyro in that system. crazyrick pointed out the finless vids and the GP750 which is the gyro I used and it did not work with any subtrim and I did not recall re-binding my set-up, in hindsight I thought that may have contributed to the problem. According to rcflier1 re-binding will not cure the issue either.
So then, regardless of what some believe and some dont,I guess if your having trouble with a drift then a good place to look would be subtrim provided you are absolutely sure it is not vibration related. Mine was creeping pretty bad during a static bench test so that very well ruled out any vibration induced causes.
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