Too much Subtrim??

[Dr.Ron]

The servo arms that came with the 450 Sport Super combo were terrible. I fiddled with switching them from the three servos and couldn't really find any combination that had the horns even close to trim.

I had to add 39 clicks of subtrim to the elevator servo and 26 clicks to the pitch servo.

That seems like a lot of clicks to get them to the right orientation. Should I go out and get a few sets of servo arms and keep trying until the subtrim doesn't have to be so severe or am I just being too anal? Using a DX7 btw.

Thanks!

Ron

[JAYHELI]

mine is the same way i wouldnt worry about it.

[Tisondm]

You're being too anal.

[Aussie_phoenix]

For my 3G flybarless system I needed as little subtrim as possible and ended up buying 10 of DS4 servo arms before I found 3 that would keep all my subtrims under 5 clicks. Seems strange but the DS4 servo arms are not all keyed exactly the same. On my flybared helis I still like to keep the subtrim under 15 clicks - not sure if there is any hard and fast rule as to what the max should be.

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[zen]

Originally Posted by Aussie_phoenix

... ended up buying 10 of DS4 servo arms before I found 3 that would keep all my subtrims under 5 clicks.

I have to admire you for that. It seems to me that if sub-trim is at a reasonable value there is better likelihood that the cyclic servos will move in concert with fewer interactions. Not that my flying ability requires the highest precision ... but I enjoy setting it up well and flying predictably.

[DominicD]

Pshhhhhhhh I've had subtrim up to and including 96, it doesnt seem to matter on modern radios.

[belcom]

same thing here on the sport. however I don't think it's big deal. those servos are mounted under angle on the sport so it's always either higher than the centering hole or lower. I found that it's best to take the heli to an open area, lift it in the air then let go of controls for a split second to see where it wants to go on it's own, set it down and then adjust the subtrims accordingly. Then try it again. At some point you will have it perfect

[vanguy]

Yeah, I never understood why some people say you should use as little subtrim as possible and what would be the negative effects if you had subtrim over 50. Of course, you should try to level your servo arms to as close to 90 as possible and let subtrim do the rest.

[Dr.Ron]

Awesome thanks!

Ron

[JAYHELI]

get your servos as close to 90 without subtrim. than use subtrim to make perfect 90. level you swash at that point. test fly heli if seems to be out of trim adjust links goin to swash to compansate. this may make you swash unlevel but your servos will still have equal throw each way. watch finless video goes into more detail

[1BADAIR]

if you think its too high or it causes issues take the servo apart like you are replacing a gear and just move it 1 little tooth

[DominicD]

Originally Posted by 1BADAIR

if you think its too high or it causes issues take the servo apart like you are replacing a gear and just move it 1 little tooth

Um this does exactly nothing.

[1BADAIR]

well it workes with the cheap eflite servo's
but he horn gear isnt keyed to the potentiometer so you can move it

[DominicD]

Every servo worth putting on a heli has the main gear on the servo connected to the pot.

[1BADAIR]

they are all connected i think. some of the gears have the matchng half moon like the pot other are just a press fit
i guess moving teeth wouldnt help subtrim but moving it on the pot would

[Dr.Ron]

I'm just anal lol.

I ordered another set of Servo Arm to see if I can get it closer to 90 without all that subtrim. I used to do that when racing Nitro Cars too, so its just me lol.

Ron

[mmarian]

The position of the servo arm is guided by the electrical feedback derived from the position of the slider of the tiny pot directly attached to the output shaft. (the one the horn is attached to). At zero subtrim the position of the pot slider is more or less in the the middle of the grafite track which is like a almost 240 deg section of a circle, so that the slider can move about 120 deg in either direction. Subtrim only sets the starting point off the centre of that grafite track. There is no any reason to believe that the grafite track resistance is more linear or consistent around the centre than it is towards its and points. It is more or less the same along the entire track. As long as the full throw can be achieved in both direction the subtrim is not going to have any detrimental effect on linearity of the movement or anything else.

[Michaelinpr]

Here is a thread I started a while back. There are a lot of views on the subject. I use a little subtrim but try for 0. Read the thread. it has some interesting arguments for 0 subtrim.

http://www.helifreak.com/showthread.php?t=187651

[zen]

To me it seems that since sub-trim uses an increment of the total available travel of the servo, a high sub-trim value must slightly reduce the end travel of the servo either at the negative or positive pitch/cyclic range. In any case there seems no reason to not get the best possible mechanical centering before resorting to sub-trim.

For the swash, perfect leveling is easily achieved at mid-stick and at full pitch in both directions. If it is deliberately tilted when the cyclic stick is centered for the sake of 'hands off hovering' or some such reason the helicopter will not perform optimally during other maneuvers. Someone said something above about putting the helicopter in the air, then taking the hands off of the control sticks and 'seeing where the helicopter wants to go' and then changing the length of the links from the servo arms to the swash plate. Not a good idea from any standpoint. Can this pilot be unaware that left thrust from the tail rotor has far more effect during the hover than in forward flight?