tail setup

[mr magoo]

Hi Guy's

I've built a trex 600e gpro dfc and having a problem with the tail. i have the tail servo at 90, as the manual say. the tail rod ends are screwed all the way in, the tail blades have approx 10mm in the opposite direction, front tail blade pointing to the right instead of left as per the manual. when looking at the rear of the heli

i thought the rod lenght could be wrong so i checked that and its the correct lenght as per manual, then i checked the tail boom is fully home and tail drive unit.

the only thing i built different from the manual was put the tail servo on the other side

if i off set the servo horm i get a tail bounce when turning to the right.

what do you guy's think i should do,

[Grumpy]

Easiest fix is to offset the horn. I offset mine because it helps compensate for the screwy geometry of the tail mechanism that means the slider needing to move further in the outward direction than inward to get equal tail pitch angle either side. The servo horn offset forward helps provide this differential movement. This is how i have mine setup and it's fine, better than having the horn at 90 degrees. If you are getting bounce then look at the stop gains in the FBL controller.

Alternatively you can gain a few mm of adjustment by trimming the ends of the plastic ball links. If you need more than that you can put a bit of heat on the end of the rod and pull off the metal cup and the screwed rod, trim the carbon pushrod and put thye metal parts back.

[coolice]

Hey buddy.

A 10mm descrepency is a quite large, I've not heard of problems like this with this model.
Have you fitted the servo round the right way in the frame cut out, eg. output spline nearer the front or rear of the model?
The output spline is slightly off centre so you can maybe flip the servo round the other way to move the offset and have some adjustability.

The tail mechanism is built as per the manual and you've not done a grip flip for instance?
.

[mr magoo]

Hi Guys

Ian i have servo spline facing the rear of the heli the only difference is its on the opposite side from the manual, the tail is built as per the manual. as grumpy has said i've had to off set the servo horn to get it setup, which i thought was weird, couple of guy in my club had a look and they couldnot work it out why.

if i have the servo horn a 90 there is no adjustment in the tail rod

Grumpy as for the tail bounce should i plus or minus the tail stop

this is what i got with the offset servo horn20141210_202509.jpg20141210_202408.jpg

[waveydavey]

You probably need to reduce the stop gain if it's bouncing. Make sure that your piro speed is the same in each direction. Not sure if it's possible with the GPro but you could also reduce the decel to stop it being so harsh

[Grumpy]

Your servo arm offset looks about the same as mine. After much fiddling around i came to the conclusion that this offset was the best compromise, not because of pushrod length (i also tried with it cut down) but to get more equal % travel either way on the servo when setting up the FBL controller.

As noted above, reduce stop gain to stop the bounce.

[coolice]

Hey Buddy.

What FBL unit are you using, a Gpro? It may just be a setup issue rather than a stop gain value change.
The Gpro requires you to setup the tail in rate mode first, adjusting the tail pushrod length to achieve a hands off hover and then flick back into heading hold mode and enjoy.
Like the last 3GX firmware's, not doing this setup for the tail produces a bounce on hard stops from one direction only usually.

The best fix for the tail travel offset is to flip the tail grips to trailing edge control off the top of my head, it's long been a trick with the Aligns, but it removes a lot if not all of the imbalance in the tail travel.

Setting the servo horn offline originally came about to balance out the action of the servo arm control ball in it's arc of movement. On the bench this saw the servo arm offline, but while flying the neutral position was one of 90 degrees to the servo in turn giving the right amount of tail pitch to hold a heading, this gave you symmetrical servo arm movement left and right.

I'd look at flipping the tail servo 180 degree's, this will give you back some adjustability required to trim the tail when in rate mode which is important to get the best from the Gpro.
.

[Grumpy]

I'm not sure putting the servo on the other side of the frame would make any difference. The mount positions are the same in either frame so it wouldn't effect the pushrod adjustment at all

I've not tried reversing the grips, i'm not sure if that works the same on the dual arm linkage as it used to on the old single arm link? The problem I've found with the dual arm is that due to strange geometry, for equal pitch range either way the pitch slider has to move a lot further in the outward (toward the blades) direction than it does when moving inward. This in turn means that servo travel has to be greater when 'pushing' the rod than when 'pulling' the rod. Offsetting the servo arm forward slightly helps minimise this difference in servo travel, but it doesnt get rid of it altogether. On the Vbar to get equal blade pitch i end up with about 90 in the 'pull' direction and 105 in the 'push' , without offsetting the arm it takes even more servo differential.

[coolice]

I'm not sure putting the servo on the other side of the frame would make any difference. The mount positions are the same in either frame so it wouldn't effect the pushrod adjustment at all

I've not tried reversing the grips, i'm not sure if that works the same on the dual arm linkage as it used to on the old single arm link? The problem I've found with the dual arm is that due to strange geometry, for equal pitch range either way the pitch slider has to move a lot further in the outward (toward the blades) direction than it does when moving inward. This in turn means that servo travel has to be greater when 'pushing' the rod than when 'pulling' the rod. Offsetting the servo arm forward slightly helps minimise this difference in servo travel, but it doesnt get rid of it altogether. On the Vbar to get equal blade pitch i end up with about 90 in the 'pull' direction and 105 in the 'push' , without offsetting the arm it takes even more servo differential.

Hey Buddy.

Ah no, I mean leave the servo in the side it's mounted but rotate it 180 degrees so the servo output spline is a little further forward allowing you to lengthen the tail pushrod to reach the new position. In turn this will allow the servo arm (I hope) to now be placed 90 degrees to the servo and also allow for adjustment to it's length. Remember to check and change servo control direction and gyro compensation direction if you flip the servo 180 in the frame.
A quick photo shop of the servo flipped in the frame attached.

You want to give the grip flip a go, I've not used it on my own models yet, but recently tried it again on a customers 450L and it does remove this imbalance in tail slider travel. All you're doing really is using the shortness of the small dog bone connecting links to put the tail blades to a pitch position which provides thrust against the torque reaction on the fuselage, at the same time keeping the controlling arm parallel to the tail output shaft for the best control geometry of equal control resolution left & right.
Of course you will need to reverse the tail servo direction and gyro sense in most cases.
.

[mr magoo]

Hi Ian

defo cant switc servo 180, then the rod will e far to short. been having a look at my heli tail setup. now what i have found when i move the tail to the left the tail it will stay there, but when i move it to the right it bounce back, so it looks like its not holding on one side. what you think. radio is jr xg14 and Grpo

stu

[Grumpy]

Hey Buddy.

Ah no, I mean leave the servo in the side it's mounted but rotate it 180 degrees so the servo output spline is a little further forward allowing you to lengthen the tail pushrod to reach the new position.
.

Ahh.. ok Ian, i understand what you meant now, that might work but it might be too much and mean that the links dont have enough engagement, i'm not sure without the heli here to check and because mine is stretched I dont have the same issue anyway.

I'll have a look at the blade grip flip idea once i get back home on Wednesday....

[mr magoo]

i decided to cut the tail rod. hopefully i'll test tomorrow