What's going on with my servos???

[steveru]

I've been flying my Trex600 for a couple of years now without any major issues. Recently, it had its first crash when the battery became unplugged whilst performing a tic-toc and it belly flopped into the ground. After replacing the usual parts it was soon back up and flying but I noticed that I was experiencing a bad swash inter-action at full + and - pitch.
I checked and adjusted all settings to ensure that at mid stick the servo wheels, aileron / elevator arms, washout arms and mixer arms are all 90 and blades are 0 pitch.
To level the swash at mid stick the sub trims were moved from Ail= R2, Ele= D3 and Pit= H9 to Ail= R5, Ele= D2 and Pit= H1.
But here's the problem, to level the swash at top and bottom the ATV's had to be altered from Ail= 113%/100%, Ele= 100%/100% and Pit= 103%/103% to Ail= 112%/110%, Ele= 85%/93% and Pit= 87%/95%.

To eleminate a possible tx/rx fault I tried another tx/rx combination which had the same irregular settings which I believe points to faulty(?) servos.

As the servos (Futaba BLS451) are beginning to move different amounts could this be the first sign that they need to be replaced or something else?

Thanks for any guidance as I'm out of ideas.

Regards,
Steve

[Aidi]

Check that the washout arms, mixer arms and blade grips do not have any twists in them.

I had much the same with one my heli's after a crash. On closer inspection it appeared that the washout arms had a very small twist in them (almost invisble unless inpsected close up).

Changed them for new ones and it cured the interaction i was experinceing.

Check everything really closely and see if something along the same lines has not happend to your head setup.

Rgds
Aidi

[Andy from Sandy]

To level the swash at mid stick the sub trims were moved from Ail= R2, Ele= D3 and Pit= H9 to Ail= R5, Ele= D2 and Pit= H1

I have no clue what you mean by those number but subtrim is used to get the servo wheels in the correct position. After that you should be adjusting the linkage rod lengths to level the swash.

Have you checked that all rod lengths are correct? Sometimes after a crash the link end can get pulled a thread or two.

[steveru]

Thanks Aidi for the v.quick reply.
I've checked all the arms and none of them are bent.
I didn't really explain myself very well in my first post that with all the ATV at 100% the servo wheels can clearly be seen moving different amounts.

Regards,
Steve

[steveru]

Evo, I checked all the rod lengths to ensure that they are of the correct length and 'matched' with each other. The sub trims on my DX7 were used to 'fine tune' the aileron / elevator arms to ensure that they were 90 and the swashplate level.

[Andy from Sandy]

The sub trims on my DX7 were used to 'fine tune' the aileron / elevator arms to ensure that they were 90 and the swashplate level.

If you are still adamant to use subtrim to get the swash level then your setup will not be correct.

[squeaky pete]

What's going on with my servos???

By the sound of it your 90 isnt actually 90, or your bell cranks are 90

[steveru]

Thanks guys for the info so far.

To elliminate any twist, bend or incorrect setting I have removed the head except for the swash, created a new model on my DX7 with no sub trim, all ATV's at 100%/100% and pitch curve set to 0, 25, 50, 75 and 100.
At mid stick (50/50) the servos are vertical (90), the bell cranks are parallel (straight line from center of servo to center of bell crank to ball joint) and the swash is level.
However at full negative the swash is leaning forward and to the left and at full positive the swash is leaning back and to the right!
Surely this must be down to a faulty servo(s) or am I going mad!!
As the servos can be seen moving different amounts I'm starting to think that some how the firmware logic within the servo became corrupted either by the 'bumpy' landing or maybe through old age as they are over two years old and have been used for hundreds of flights.

[Boggy]

cant you now just use your end points to level the swash at high and low points??

[steveru]

I can but the difference between each servo is conciderable e.g Ail= 112%/110%, Ele= 85%/93% and Pit= 87%/95% which solves one problem yet creates another.
With these settings the swash is level throughout it's entire range top. middle and bottom
However, when applying full right Aileron at full negative I get binding on one side between the swash and bearing block whereas on full left Aileron there is a no binding and the gap is significant.
I just can't understand what has changed!! Previously the servos were close to each other at 100/100, the swash was level throughout, I had +/-13 pitch and 8 deg cyclic.

[squeaky pete]

What's going on with my servos???

If u get binding now your gonna get binding after coz effectivly ur making the servos do what they shld be doing neways, even tho ur using endpoints u hav still got the problem that u wld hav anyway, 8degrees is 8degrees, using end points or not

[Hangar-7]

After replacing the usual parts it was soon back up and flying but I noticed that I was experiencing a bad swash inter-action at full + and - pitch.
Steve

Silly question, but "usual parts include" mainshaft and feathering shaft? I had similar problem with my Pro450 which eventually turned out to be ever so lightly bent feathering shaft.

Worth a re-look.

[steveru]

I'm sorry if I appear to be a muppet but one of us is missing the point.
Before the 'bumpy' landing the heli was set up (perfectly) with +/-13, 8 deg pitch and the swash was level with very little ATV's.
Now the servo's require a lot of ATV's to ensure equal travel (pitch) but the Aileron cyclic (side to side) is now not even probably 9 deg right and only 7 deg left.
Hopefully, I will have it fixed before Grassroots day or I'll show you what I mean.
Any further guidance greatly received as I just want my Rexy back

[steveru]

Silly question, but "usual parts include" mainshaft and feathering shaft? I had similar problem with my Pro450 which eventually turned out to be ever so lightly bent feathering shaft.

Worth a re-look.

Thanks for the suggestion but the 'bumpy' landing wasn't that bad.
During strip down I checked the feathering shaft when I changed the main blade grip bearings and it was fine.

[Bigbellypopper]

Have you checked that the splines on the servo horns are not stripped or damaged? - Also check the servo gears for damage....