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-   -   sub trims ? Neutral ? -120, + 120, totally confused! (https://www.wattflyer.com/forums/showthread.php?t=73750)

denvoyager 05-16-2014 09:29 AM

sub trims ? Neutral ? -120, + 120, totally confused!
I'm making the transition from 35 to 2.4 systems, and have a Turnigy 9X transmitter. I'm getting into it, and my cantonese mentality re the manual is improving rapidly!
It does not help in the 'set up', just in the 'do this' to alter /save/exit etc.
That's ok, but I need to know how to set the sub-trims on each model.
I understand about tiny servo to 90 deg adjustments etc., but the main things I need to understand are these points:

What is a sub-trim, and what does it do?

Where is the neutral point, and what does it mean?

Why are there two ranges swinging from -120 to + 120 degs.?

...also a step by step would be good, if anybody knows of a url to try!

Thank you,
Den ,
Cymru (Wales)

JetPlaneFlyer 05-16-2014 10:25 AM

Sub trim is similar to what the normal trims do on the Tx. They adjust the position of the servo neutral point which is good, for instance, if you want adjust the arm to be perfectly at 90 degrees,or if trying to adjust a control suface that has no mechanical adjustment on the pushrod.

Generally you should try to keep the amount of sub trim as low as you can, using too much can mean that the servo over-travels and might mechanically bind.

fhhuber 05-16-2014 02:52 PM

The travel range adjustment from +120% to -120% is compared to the old standard rotation range when using a basic radio. The added travel range really doesn't give you much more control throw range as the rotation has the hole in the servo arm moving more sideways then in line with the pushrod.

Most modern digital servos can make use of this added rotation as most of them can be programmed for 180 deg or more without encountering a mechanical stop. Most of the older analog type servos (and some digitals servos) will have a mechanical stop to prevent over-ranging the position sensing potentiometer.
You have to check with your servos' instructions to see which can safely rotate how far.

The linear servos in Parkzone/E-Flite Ultra Micros CAN NOT withstand more than 100% (according to Spektrum's travel range). Going too far will lock the servo. (You can get there with the trims + full stick at 100% in some cases) You can power down and hand wind it back into the middle and it will work again but since the overtravel usually happens in flight you'll damage or destroy the model.

Note also that 100% travel by one brand is not necessarily the same degrees of rotation as some other brand's.... and there is some deviation between any 2 transmitters.


Neutral point is where you want the servo to stop when the stick is centered.

Trims adjust the whole stick range. Neutral point doesn't affect the endpoints, just the centering.

denvoyager 05-17-2014 07:29 AM

neutral point definition
Thanks for the replies!
Can I ask a question which seems to be stating the bleeding obvious?!:
(1),on the transmitter, the neutral point number is zero ( 0 ) (after you've chosen its 'rest' place at physical centre), and
(2), either side of that there is a 120 deg 'swing') (which can be adjusted on the transmitter).

I understand that the different servos have different behaviours/ parameters,all mine are analog, I think.
I will also have to get used to the receivers being 'dedicated', and unusable in any other aircraft unless 'fooling' the transmitter by using the same name. I'll have to label them!
There doesn't seem anywhere that provides info on basics so I'm having to ask around!
Thanks once again, Den

JetPlaneFlyer 05-17-2014 09:04 AM

The +/- 120 isnt degrees, it's just increments, each digit is far less than a degree. But you shouldn't use anything like the full 120, use mechanical adjustment (move arm on it's splines) to get the servo as close to possible and sub-trim just for the final 'tweak'.

With the 9x you can swap the receiver in and out of as many models as you want. The 9x does not have a 'model match' feature (like Spektrum) that binds the Tx to any specific model memory, so you can if you want move the receiver from model to model with no need to re-bind. To be honest though with the price of receivers being so low it's not really worth the hassle.

fhhuber 05-17-2014 03:06 PM

Note the picture of the rotation angles. We just need to look at that picture.

default neutral point is where they show the arm.
The normal +/- 100% throws are 45 deg each way from neutral point.
Then the "180 deg" version is 90 deg each way from the neutral point (90 + 90 = 180)
120% of normal throw would be 1.2 * 90 = 108 deg or 54 deg each side of the neutral point.

Resetting neutral point and not changing the endpoints might have the servo "center" 5 or 10 deg (however much you changed it) to one side, resulting in less travel one way and more the other vs that new neutral point.


When a cheap RX was $125, minimum wage was $1.25 and a new VW Beetle was about $1200... it made sense to move the RX from model to model.

With a new RX being $50 (for a real Spektrum 4 ch... and some off brands being about $20) minimum wage $7.25 and a cheap new car being $17,000... it doesn't make as much sense.

I have somewhere near 40 old 72 mhz RXs and between 30 and 40 2.4 ghz RXs.... and enough aircraft to use them all.

kyleservicetech 05-17-2014 05:57 PM


Originally Posted by fhhuber (Post 948573)
When a cheap RX was $125, minimum wage was $1.25 and a new VW Beetle was about $1200... it made sense to move the RX from model to model.

With a new RX being $50 (for a real Spektrum 4 ch... and some off brands being about $20) minimum wage $7.25 and a cheap new car being $17,000... it doesn't make as much sense.

I have somewhere near 40 old 72 mhz RXs and between 30 and 40 2.4 ghz RXs.... and enough aircraft to use them all.

Holy crap. Thought I was doing good with a dozen models ready to fly. :oops:

As for Spektrum 4 channel receivers, even their prices have dropped. This is a full range $30 receiver that a lot of my club members are using in their 100 MPH foamies. Absolute reliability. I've got on in my receiver collection.


My first four channel RC system was picked up in 1964. That system was a Microavionics 4 channel that cost the equivalent of 6 months rent. It was used at two years old. That POS radio averaged 20-30 flights between in flight failures. Still got a Craftaire single push button channel type transmitter and receiver on the old CB frequencies. It still works.

hayofstacks 05-18-2014 05:58 AM

I use sub trims on my planes that i bend my own pushrods for. i just use the that looks about right method, then use the sub-trims to get them straight before a maiden.

denvoyager 05-18-2014 07:53 AM

Got there in the end!
A huge thank you for all your replies. You are all obviously well down the line in terms of experience, but at my stage I'm still crashing on a regular basis! Thus the receiver usage, not economically driven, Turnigy receivers (8ch.) are very well priced!
I feel that the help I have received from everyone has explained the use and advantages of sub-trims really well. So thanks again, from
Den, Cymru (Wales)
P.S. Brill site!

fhhuber 05-18-2014 08:10 AM


Don't get overly dependant on the sub trims and ATV...

And ensure that you CLEAR MODEL MEMORY when setting up a new model.

The sub trim, neutral point and ATV functions if not cleared can get you into trouble. Adding the adjustments over a few models can end up with no available travel at all one direction.

EVERY model you set up:
Clear memory.
Center up the servos.
Get the surfaces adjusted mechanically as close as possible to desired throws and centering.
THEN start dealing with the computer functions.

I even make sure the ailerons work properly on a Y harness before I move one to the aux channel for flaperon function.

denvoyager 05-19-2014 08:10 AM

Great !....but what's an ATV!!!?
I'm probably the world's worst at figuring out initials et al, although I do know that FPV is 'first person view'!
I see the logic that you have laid out - carry out standard good practice with the mechanicals, then progressively 'fine tune' with the electronics. I've finally arrived! Yippee!
Thanks again, Den,
Cymru (Wales)

solentlife 05-19-2014 11:20 AM

Denvoyager ....

Rx .... they are basically dumb on mots radios including 9x ....

they are bound to a Tx ... but not specific to a model. The model settings are in the TX ....

You can set up 8 models in the Tx .. all with different settings. Have one Rx and swap between the 8 models. As you change model memory slot on Tx - the Rx will receive it's instructions based on THAT model memory.

ps ... inmy signature is the 9x FlySky yahoo group - where you can get a decent translated manual ... all the help you need.

fhhuber 05-19-2014 01:45 PM

ATV = Adjustable Travel Volume = the 0 - 120% range when applied to both directions at the same time.

EPA = End Point Adjustment = adjusting just one end of the travel range at a time.

Differential ailerons can be looked at as a special version end point adjust where you are doing it for 2 channels at once usually to have more upward aileron travel than downward.
Can be accomplished mechanically too.

You can do a lot of the adjustments mechanically. The computer just makes it easier to fine tune the adjustments.

denvoyager 05-20-2014 07:25 AM

Thanks again!
Thank you both. I will try that site, Nigel, although I'm beginning to realise with the manual for the 9X that the flow charts are best to follow, the text can be convoluted!
Have spent the time setting up a 'Tucano' I've been given, and am using your advice to set up the servos etc.
Den, Cymru (Wales)

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