yaw right = bounce back; yaw left = chasing

[spudz11]

Hey folks,

Got a Trex450 proV2, /w DFC head.

Just come out of some maintenance, replaced main shaft bearings, front tail gear bearings, and also upgraded my 450MX motor to boca ceramic bearings. At the same time, I upgraded my 3GX to v5 firmware. Its sounding all nice and smooth!

My heli's issue is as the title states... when flying in head lock mode, my tail is pretty damn stable, no erratic hunting, but the tail response is a bit weird. I've only had one flight post maintenance/3GX upgrade, and I was testing my rudder gain by doing some hard yaw stick and watching for bounce/oscillations, or a solid stop at max gain.

I found that when doing a hard right yaw and stop that the tail would bounce back about 4-5 inches to the left. But when doing hard left yaw and stop, after the initial stop the tail would chase and continue left for a small burst, about the same 4-5".

I have a bit of subtrim set during DIR setup to get the tail servo to 90 degree, and adjusted the rod length according to the DFC manual, i.e. 4mm spread between the tail blades (which i presume is to induce a slight right yaw at neutral tail pitch to compensate the main blade rotation) that said, i noticed in the 3gx v5 manual it shows tail setup to be 10mm between-blade spread, a huge amount different from the 4mm recommended in the dfc manual

In software setup, rudder delay is set at 0 by holding the stick to small heli size and holding the stick there until the setup times out to retain the 0 delay.

I haven't had a chance to try tweaking the delay yet, I'd try 10 next, or to tweak the tail control rod length a bit to increase/decrease that 4mm spread between tail blades at all. Just wondering if what I'm seeing is a specific symptom of a known cause with a known cure. Also, I didn't think at the time I had it in the air to put it in rate mode and see what neutral tail balance is like without the rudder gyro active... guess that should really be the next step.

Any specific suggestions?

Thanks,
Brian

[Felix the cat]

Quick and perhaps silly questions / sugestions:

Have you centered the tail, if so, how ?

How's your slider travel in rate mode, how does in center in rate mode, while in rate, fold the tail blades towards each other and check alignment.

When you say a little sub-trim, how much are we talking about ?

On 3GX the whole servo at 90°concept; while it's the ideal condition, can be over-rated. Because not always you have horns that will achieve it without sub-trim.

I'd rather go with horns as close to 90 as possible, with little or no sub-trim, leveled swash, 0° mid stick, +- 12° collective and 8° cyclic and they work just as nice.

3Gx is one finicky unit as far as sub-trims, vibrations, ect. I have four of'em on different birds from 450's to 600. I'm a firm believer in mechanicals first and softwares later. Usually I leave the default values until it flies spot-on and then tweak the software if needed.

Hope this helps some

[spudz11]

Thanks, FTC.

My rudder subtrim is at 13R. Is that too much?

As for centering the tail, I mentioned some competing views on method I've read from the various pro v2, dfc, and new 3gx v5 manuals. As you said, in range mode, fold up the tail blades and compare the tracking. I set it to

4mm spread between the tail blades (which i presume is to induce a slight right yaw at neutral tail pitch to compensate the main blade rotation) that said, i noticed in the 3gx v5 manual it shows tail setup to be 10mm between-blade spread, a huge amount different from the 4mm recommended in the dfc manual

This is what I'm referring to

ProV2 manual:


DFC:


3GXv5:


I've ignored the pro v2 instructions to center based on the slider inside and outside space, as it depends whether you fully have the blade grip anchored to the correct extent of the tail shaft.

Otherwise, it was raining this afternoon so I couldn't take it up and check its true neutrality in rate mode during flight. I have a feeling that I need more right yaw pitch at neutral (i.e. 10mm blade grip tracking breadth) perhaps the new software runs like that and expects it.

This seems like a logical possibility, because on right rudder and stop it might be bouncing back left if it is expecting a greater rightward yaw effect at neutral stick than it is getting, thus the bounce back left isn't so much caused by incorrect gyro intervention, but rather the gyro expecting the tail to stop if it were correctly dialed in to 10mm tracking bias.Then, the gyro kicks in after that initial bounce.

Similar reasoning could be used to explain why the tail chases leftward after left rudder and stop.

meant to say that the slider is nice and smooth, as is the control rod through the support islets... I've done that poorly before, and its the first thing I check when the tail is off.

I don't think it is vibe related, everything seems pretty smooth when pieced apart.

Thoughts? Of course I'll tinker and report back when I get a chance.

EDIT:
few extra points to consider. Both my rudder right and left travel limit show up as equal and opposite, +/- 56. Also perhaps my gain is just a bit too low... I didn't try going up too high considering the weird behaviour, but I've got it at 30% on my Tx, which shows up as 16 in the 3GX software. I know gains vary between setups, but it is substantially less than the post here https://www.helifreak.com/showthread.php?t=634446 (24 in 3GX software) on setup for same 450 rex on this same 3gx firmware version.

[skunkworx]

Set it up in rate mode. When you go to pick it up off the ground, it will likely pull to the right or the left and you adjust your linkage rod until it stops drifting. It won't completely solve the drift since rate is supposed to be subdued, but as long as the nose is pointed toward the wind and it stays relatively straight then you should be able to find the true center position.

Once you have the center fixed, set end-points and then tune your EPA and gains until you get a consistent throw and reaction on both sides. This takes a bit of playing around with so be patient, but in the end you'll get a very locked in tail and you develop the "feel" of how it needs to be for most machines.