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subtrim vs trim

#1
hey guys. got a question for you. hopefully i'm posting this in the right place.
my buddy and i both set up new model linkages as close to perfect as possible but when they are just a touch off mechanically he always uses subtrim to fix it whereas i always just hit my trim tabs on my transmitter for a few clicks. i really don't think either one of us is using excessive trim the question is which is better using subtrim or actual trim . he thinks if he uses subtrim he is more likely to get equal throw both directions but this makes no sense to me as it seems the servo itself has a defined range whether you put in trim using trim tabs or sub trim you are going to sacrifice complete bidirectional throw either way.
anyone have an opinion regarding this?
k.t.
 

colorex

Rotor Riot!
Mentor
#2
As I learned by reading two Tx manuals and lots of forums, you set up trim first, then you fine-tune it with the sub-trim. Sub-trim will only be worth it if your control linkages have absolutely no slop in them and you are using high quality servos. I also think sub-trim has more precision, but less range.
 
#3
thanks for the info. i see you are located in ecuador. i have been there twice. landed in quito and climbed mt.cotopaxi once many years ago. i'll be flying near quito is difficult due to the altitude/thin air!
kt
 

Ak Flyer

Fly the wings off
Mentor
#5
I use sub trim for mechanical alignment and then use my flight trims to account for cg issues or other setup problems that I didn't get right on the ground. On my DX8 the sub trim is much finer than the flight trim, but you can adjust the increments on your normal trim. On most radios the sub trim is only 1 step where the flight trim might be 4 or 5 steps. Say you are trying to align your servo arm and you can't get it at 90 degrees because the teeth are just a little off. You can use the sub trim to center the servo arm before continuing. The nice thing about using sub trim for this is that when you use your in flight trim, you don't lose the centering from your sub trim. This keeps your servo alignment correct. Then you can make mechanical adjustments to your push rods and control horns while keeping the centering of your servos. If you have more than a very small amount of adjustment then all your efforts should towards mechanical corrections.
 

jetpackninja

More combat please...
Mentor
#6
AK speaks wisdom.
Colorex is not wrong, if I understand what he's saying correctly.
Ninja says.
Trim as well as you can mechanically
then
Use sub trim to fine tune your mechanical trim (like AK says, to get your servo arm to cenrter at 90 degrees etc.)
then
Use in flight trim to make adjustments on the fly. I like to have my trims centered for normal flight so much of my adjustments on maiden are adjusting mechanical trim.
 

lobstermash

Propaganda machine
Mentor
#7
I often use subtrim as a lazy alternative to mechanical trimming... As in, I'll try and trim the model out in the air, but if there's only just not enough trim (fairly uncommon, but it does happen), I land it and set the main trim back to centre and subtrim to the almost correct. Very bad to do, because if you change transmitters or overwrite that model, subtrim gets forgotten.
 

jetpackninja

More combat please...
Mentor
#8
Yeah- agreed. Have done myself. And then left the radio turned on overnight and the subtrims reverted back to 0. Live and learn I guess. (DX6i)