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HelicopterRadio - Servo - Gyro - Gov - Batt › JR G7703D vs JR G7000T
11-29-2007 05:36 PM  10 years agoPost 21
fiveoboy01

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Waunakee, WI - USA

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If there is any drift of the servo, use the sub trim of the TX tail rotor channel to stop the drift. What you are doing when you do this is setting the TX internal standard for that channel, to match the internal standard of the gyro.
From your description, it appears that this step is performed on the bench, not during flight. How does one determine if the servo has drift on the bench?

Mikado Logo 400, hopefully ready by spring.

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11-29-2007 05:55 PM  10 years agoPost 22
SteveH

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Yes, it's done on the bench in heading hold mode. If there is drift, the servo will slowly move. Adjust the sub trim on the channel so it does not move, but again, you must be in heading hold, and again, it's all in the instructions. You do read the instructions, don't you?

The government cannot give you anything without first taking it from someone else.

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11-29-2007 06:30 PM  10 years agoPost 23
fiveoboy01

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Seeing as how the servo is zero deadband, it moves/twitches on the bench regardless. How am I to know if it's due to drift or simply normal operation?

FWIW, there is ZERO mention of the procedure you just explained in the manual and not one mention of subtrim anywhere, except in the beginning where it states to set it at 0%....

Mikado Logo 400, hopefully ready by spring.

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11-29-2007 06:47 PM  10 years agoPost 24
SteveH

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Is this a 770 gyro you are talking about? If so, I said earlier that I had the 7000 and 500T gyros.

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11-29-2007 07:13 PM  10 years agoPost 25
fiveoboy01

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Yes 770... The instruction "manual" is basically a smallish piece of paper.

Mikado Logo 400, hopefully ready by spring.

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11-29-2007 07:24 PM  10 years agoPost 26
DS 8717

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It doesn't need a book like the futaba does.

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11-29-2007 07:27 PM  10 years agoPost 27
DS 8717

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The futaba gyro seems to be more tolerant of a sloppy system than the JR does. The 770 is an overkill for the 450.

YOU ONLY LIVE ONCE..IF YOU LIVE IT RIGHT THATS ALL YOU NEED

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11-29-2007 09:31 PM  10 years agoPost 28
xxcysxx

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Baltimore, MD - USA

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when you guys say the tail drift, is this the same as when i saw the tail servo creeps when i power it up on the bench. it keep creeping slowly until it max out it maximum deflection.
i had this effect on the MS gyro. what i did was add some sub trim and the creeping stops, it hold just fine thereafter. i had a few futaba gy401 and it doesn't creeps like this.
but i guess every gyro just design differently.

Tam

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11-29-2007 09:46 PM  10 years agoPost 29
SteveH

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Texas

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when you guys say the tail drift, is this the same as when i saw the tail servo creeps when i power it up on the bench. it keep creeping slowly until it max out it maximum deflection.
Yes, and part of the setup, at least on the JR500T and 7000, is to use the sub trim to stop it.

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11-29-2007 11:22 PM  10 years agoPost 30
xxcysxx

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Okay, wait a minute. Now i'm confuse.
The purpose of sub trim is use to re-center the servo to a new position. Like i use sub trim some times to "trim" it a little bit to get it perfect center. So if the subtrim function is use to eliminate the drift/creepy servo, then i basicly loose the sub trim function re-center the servo. Because everytime i use sub trim to trim the rudder, the tail would drift/creeps.

like i sometimes when i hover my heli and it want to wander in a certain direction, i use sub trim on my elevator or aileron to counter it from wandering in that particular direction.
But the rudder will loose this function because the rudder sub trim is use to stop the drifting/creeping.

Tam

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11-29-2007 11:42 PM  10 years agoPost 31
tadawson

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Lewisville, TX

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The purpose of sub trim is use to re-center the servo to a new position. Like i use sub trim some times to "trim" it a little bit to get it perfect center. So if the subtrim function is use to eliminate the drift/creepy servo, then i basicly loose the sub trim function re-center the servo. Because everytime i use sub trim to trim the rudder, the tail would drift/creeps.
On a heading hold gyro, subtrim CANNOT and WILL NOT adjust the center point of the servo! Period! The rudder channel into a gyro is commanding a piro rate, and not a servo position by it's design. If the center point of the servo is off, you set that with the linkages, or an offset adjustment in the gyro, if it has one. I think this basic misunderstanding is why so many folks get into trouble with the JR gyros - they just don't fully understand the interaction of the radio, gyro, and servo. The mismatched "neutral" between radio and gyro does NOT result in an offcenter servo! It results in a command to the gyro for a slow piro in one direction or the other. That's why, on the bench, the
servo goes all the way to the stops, and not just a tad and sit there. When you subtrim, you take out the piro, and tell it to sit stationary.

- Tim

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11-30-2007 12:01 AM  10 years agoPost 32
fiveoboy01

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Waunakee, WI - USA

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Tim, thank you for that explanation, it was helpful.

My understanding after your explanation is that no subtrim is needed as long as the servo arm does not slowly move one direction on the bench(ignoring the normal jittering of a zero band servo). Hence, the only way to stop a very slow drift in flight, if the servo is staying stationary on the bench(in my case it takes about 10 seconds for the tail to move 45 degrees) is to adjust the linkage...
Please correct me if I'm wrong on any of that.

Mikado Logo 400, hopefully ready by spring.

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11-30-2007 01:00 AM  10 years agoPost 33
xxcysxx

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Baltimore, MD - USA

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hi Tim,
i have a question, and its about the temperature compensation of the gyro. i read in the g7000t gyro manual it mention that you should let the gyro sit in the outside temperature for at least 12 minute for the gyro sensor to neutralize with the temperature before starting it up.

so my question is why? is every gyro has to do this. what's with the temperature and the sensor. i really don't understand the whole idea about temperature compensation of the gyro. though i do let all my models sit outside for a little bit before i fly. i just want to get a better understanding of it.

thanks

Tam

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11-30-2007 06:48 AM  10 years agoPost 34
tadawson

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Lewisville, TX

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All electronic components change value in a subtle manner with a temperature change, and the heart of the gyro, the piezo/smm/whatever element, is suceptible as well. So, if the temp causes it to drift, the setup will change, and you will see it as a slow rotation. No big deal - just trim it out on a JR, or reinit the gyro on a Futaba to get rid of it (you can also trim it out in flight on a Futaba, but that's not a "published" method . . . ).

- Tim

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HelicopterRadio - Servo - Gyro - Gov - Batt › JR G7703D vs JR G7000T
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