Need advice on oscillating tail after GP780 fitted

[JacquesC]

I need some advice please :
I converted two 450 heli's (one 450 SE V1, the other an older 450 XE) to use the DS420 tail servo and GP780 gyro since the previous setup (analog servo and Futaba GY240 gyro) did not do well in heading-hold mode.
Both gyro's are also connected to my gear channel to set the gain.

Now, both are doing just fine in non-H/hold mode, but when I switch to heading-hold then they exhibit some tail oscillation. Iv'e lowered the gain but the only difference is that it then changes from rapid hunting (too high gain) to slow oscillations thru about 30 -45 degrees of tail-swing.

All settings on the gyro are correct and the heli's are otherwise in fine shape.
I also experimented with the Delay settings on the gyro's but with not much success.

Now I have to point out that both heli's are NOT using the standard Align ESC's - which is a 6 volt system, but older ESC's which is 4.8 or 5 volt ESC's - the reason being that the rest of the servo's are older 4.8 volt servo's which I don't want to replace.

Could it be that the DS420/GP780 combination is not happy to operate at 4.8v, even though both are capable of doing so according to the specs ?

I've run out of ideas about the cause of the problem.
Lastly, both servo's and gyro's are brand-new and in working condition.

Any suggestions or advice will be highly appreciated !

[runesb]

get rid of the ds420 and mount hs 5084 or futaba servo.. your tail should fine then

[srt4tom]

Try moving the ball on your servo arm in closer to the center.

[JacquesC]

I tried moving the ball link closer to the center but that did not make any difference at all.
@Runesb - replacing the servo (or gyro) will be my last resort, even though it's starting to look like I will have to do something like that - what a pity because it will mean that I wasted money doing the upgrade

In rate mode both heli's behave impeccably.
I also inspected the belt on the XE and it's perfect, whilst the SE also got a brand-new belt.
There is also no slop, wornout bearings, or defective tail components to be seen.

Anybody else with any suggestions ?

[faithalone]

Originally Posted by JacquesC

Now I have to point out that both heli's are NOT using the standard Align ESC's - which is a 6 volt system, but older ESC's which is 4.8 or 5 volt ESC's - the reason being that the rest of the servo's are older 4.8 volt servo's which I don't want to replace.

Could it be that the DS420/GP780 combination is not happy to operate at 4.8v, even though both are capable of doing so according to the specs ?

I've run out of ideas about the cause of the problem.
Lastly, both servo's and gyro's are brand-new and in working condition.

Any suggestions or advice will be highly appreciated !

I do not think that the voltage would matter much - could you add an inexpensive ubec and run it at a slightly higher voltage to test? also just basic stuff like disconnecting the servo rod from servo and making sure there is no binding on the tail assembly and everything is tight back there - try another servo horn on the rudder servo to see if the different geometry helps out - i am sure you have checked but gain plug in correctly? -

just trying to throw some stuff out there - HobbyWing makes a fairly cheap but decent Ubec that you can find for less than $10 - just do a search on google and then click on the shopping link and several retailers come up -

best of luck!

[Silver-techie]

Hmmm...

My 450's use 4.8-5.2v ESC/BEC. So I don't think that would be a problem.

I have a GP780 (JR DS290G servo) installed on a 250, and it's pretty finicky. I have to set the gain really low for HH mode, and I still get lil wag's but can hover okay with it. So I'm still in the process of tinkering with it.

Only advice I have that I didn't see mentioned, is to check for any serious binding. The tail servo rod should move like butter..

A lil slop on the tail I think is okay, but to make it as perfect as possible would be a major plus.

[faithalone]

Originally Posted by Silver-techie

I have a GP780 (JR DS290G servo) installed on a 250, and it's pretty finicky. I have to set the gain really low for HH mode, and I still get lil wag's but can hover okay with it. So I'm still in the process of tinkering with it.
.

Had a very slight wag on my 250 - i mean so small that even my ocd could cope with it - and this was using my Quark gyro - I finally rebuilt the tail because I noticed a very slight amount of slop and this cured it completely and now my OCD is very happy! Lol

[runesb]

I had the same opinion that the ds420 should work. Never have my tail behaved normaly, so last week it did... Steady tail and a hs5084. And im happy about the 450 for a change.

[MattFL]

My gp780 is extremely vibration sensitive and the vibrations cause wag. Search here and I posted my solution with pictures. Basically relocated the gyro to the font where I could use a mount made of a steel plate sandwiched between two foam pads.

[JacquesC]

Thanks guys for all the replies - it looks like the whole tail setup is somewhat finicky.

The tailrotor assembly is very smooth with no binding on the one heli, somewhat less so on the other one.

I think I will go through each and every thing and make sure everything is up to spec, including the tailrotor hub bearings. If still not cured I will put back the previous servo that was on and then work my way through all the suggestions until I have it sorted.

This might take a couple of days I imagine because it is rather windy here most of the time now.

I will report back on this.

[newbheliusr]

The problem is the DS420 is not up to the task. Either get a DS520, 5084mg, or S9257 and your problems will disappear. Trust me.

[runesb]

Originally Posted by newbheliusr

The problem is the DS420 is not up to the task. Either get a DS520, 5084mg, or S9257 and your problems will disappear. Trust me.

[nashus2002]

Originally Posted by MattFL

My gp780 is extremely vibration sensitive and the vibrations cause wag. Search here and I posted my solution with pictures. Basically relocated the gyro to the font where I could use a mount made of a steel plate sandwiched between two foam pads.

+1 on that, i fixed my tail wag like this and remember not to strap down the gyro or zip tie the wires for the first 5cm. all that conduct vibs to the gyro.

[Silver-techie]

Originally Posted by newbheliusr

The problem is the DS420 is not up to the task. Either get a DS520, 5084mg, or S9257 and your problems will disappear. Trust me.

I agree. The DS420 is more for a 250 class (I have it on my 250 FBL setup). 450, you got more torque action going on, so it's going to struggle.

Spec on torque:

DS420 - Stall torque: 0.75kg.cm
DS520 - Stall torque:1.9kg.cm(4.8V) 2.5kg.cm(6.0V)

DS520 would also work on a 500 class.

For my 450's I ended up using walkera:

HM-V450D01-Z-15: High Speed Tail Digital Servo (WK-2601H), Newest version For V450D01, Align Trex450 & Compatibles

Specification
Modulation: Digital
Torque: 4.8V:28.0 oz-in (2.02 kg-cm)
Speed: 4.8V:0.08 sec/60°

Only thing I kinda hate, if the horn breaks or the hole strips for the ball linkage.. I can't seem to find a good horn replacement. Other then that, it seems to be a pretty reliable tail servo, in my opinion.

[JacquesC]

Okay, all noted on the DS420 maybe not the best choice and also on the sensitivity of the gyro.

I picked up a very slight looseness on the one tailblade holder which was easily fixed by tightening the bladeholder screw which firmed up the whole tailrotor hub assembly.

I quickly tested the heli early this morning and VOILA ! - tail seems to hold pretty still now !
This is quite a relief and I can now turm my attention to the 450 XE and see if I can get it working as well. But before I do that I have to do some repairs to the landing skids which got broken on the last test

Thanks for all the advice and recommendations, much appreciated !

I will keep you posted on my progress with the XE.

[MattFL]

Originally Posted by Silver-techie

I agree. The DS420 is more for a 250 class (I have it on my 250 FBL setup). 450, you got more torque action going on, so it's going to struggle.

Spec on torque:

DS420 - Stall torque: 0.75kg.cm
DS520 - Stall torque:1.9kg.cm(4.8V) 2.5kg.cm(6.0V)

DS520 would also work on a 500 class.

For my 450's I ended up using walkera:

HM-V450D01-Z-15: High Speed Tail Digital Servo (WK-2601H), Newest version For V450D01, Align Trex450 & Compatibles

Specification
Modulation: Digital
Torque: 4.8V:28.0 oz-in (2.02 kg-cm)
Speed: 4.8V:0.08 sec/60°

Only thing I kinda hate, if the horn breaks or the hole strips for the ball linkage.. I can't seem to find a good horn replacement. Other then that, it seems to be a pretty reliable tail servo, in my opinion.

Do you need any align horns? I have some spare align horns and I can send you a few if you need them. Actually I still have 3 or 4 align ds410m servos that work if you want some spares for cheap.

[Silver-techie]

Originally Posted by MattFL

Do you need any align horns? I have some spare align horns and I can send you a few if you need them. Actually I still have 3 or 4 align ds410m servos that work if you want some spares for cheap.

I have align horns spares, from a DS410 and DS420. They don't fit the Walkera tail servos, which I do like on my 450's. Heh.. I tried all the spares I have from other servo's and they won't fit.

Kinda wonder if I could get one of them aluminum horns that can fit different sizes gear on the servo.

More then likely I'll use the horn I have till it actually fails or breaks.