Collective pitch adjustments.

[TheDarkPassenger]

Hi,

On the home run to setting up a Trex 250, last thing that's giving me grief is getting an even pitch and cyclic.

0 pitch is slightly below center stick and I think that's why I'm getting issues with +12 and -10 (or the other way around) on collective and +7 and -5 on cyclic (or t'other way around)

The ball link adjustment on the blades is fully screwed in so no more adjustment there.

The only thing I can think of is to use subtrim on all three servos to bring the swashplate down a little.

Question is: Is this correct or is there a better way to do it, as so far, every time I've adjusted one thing, something else seems to be out of kilter and in the words of Sean Ryder "it's twisting my melon"

[Delarado]

Is it FB or FBL?

Try to set it up initially so your servo arms are at 90 degrees at mid stick (using subtrim and mechanical adjustments of the servo arms themselves) and you have 0 degrees collective, then you shouldn't have any problems from that point forward.

[TheDarkPassenger]

Thanks for the reply.

It is FBL, I've tried to get it at 90 degrees (using subtrim and swapping servo arms around) however this needs a lot of subtrim, 40+ in some cases. Is that normal?

I've measured the length of the rods (3 times now) to match the manual.

[GIXERMAN]

The manual is only a guide.

[Delarado]

40 subtrim is fine, ive used 110 on my models before.

Rod length doesn't necessarily need to match the manual its just a starting point.

You should set servo horns at 90 degrees (with the fBL controller in whatver setup mode it uses, DIR for example for a 3gx)

After this use the link lengths in the manual. Check you have 0 pitch at mid stick. If not adjust hte link lengths to give you this, then work from there.

[TheDarkPassenger]

Spot on, thanks all.
Looks like the head is coming of for the 15th time this week

This machine WILL be in the air by tonight.

[Delarado]

HAha indeed. Leave the head on for now. Set your servo arms to 90 degrees using sub trim by eye, then measure and make sure you have 0 pitch on both blades at all areas of the rotor disc. (Rotate the heli and not the blades to check this if using a digital pitch gauge, unless the bench is completely level)

If you dont have 0 pitch adjust the appropriate links. The servo - swash links if both blades are out. The swash - blade grip link if one blade is out.