JR G770T Gyro troubles

[Gavin2407]

Hi everyone. Current heli specs as follows

TT Raptor 50 Titan
TT 50 pro Engine
Standard 539 Servos (Elevator,Aileron,Pitch & Throttle) (Want to upgrade these to 9252 soon)
JR G770T Gyro with JR 8900 Tail Servo
JR 2610 TX
Assigned gear channel to Aileron switch (Elevator is combined for both A & E dual rate/exp)
Rudder ATV is +150, -150.
Gear ATV is +85 for HH & -85 for rate mode
Servo arm length is 13mm and not binding

Tried tail setup whereby there is 4.5mm between tail case and brass bushing
Tried tail setup whereby the tail pitch control lever is parallel with the tail rotor shaft
Can't get a setup that there is 4.5mm gap and control lever is parallel with the tail rotor shaft.
Gains are very sensitive and any higher or lower settings only make things worse

I converted all my electronics from a Raptor 30V2 into the Titan but can't seem to get the tail sorted. If I get it to not drift in HH then rate mode is way out and she starts drifting nose left in hover but jumps nose right when rapid throttle is given. The same happens when I get rate mode sorted then HH mode is gone mad. Currently got everything set up as per manual but don't know if I'm missing something.

If anyone has any ideas, please reply as i've just started getting my figure 8 right so don't want to be bogged down by an inconsistant tail.
 

[spacey]

I'm not famillier with the Raptor so I can't help on the whole 4.5mm thing you talk about? Care to help here?

I'm also not sure I understand exactly what the main problem is?

First I have to ask about the basics.

You're sure the tailrotor is turning the right way yes? And that the tail rotor blades are on the right way around?

There's no bad vibrations on the heli whatsoever and the motor is tuned properly, it's bearings also in good shape? Bad motor bearings will make this gyro freak out completely!

What tailblades are you using?

The tail pitch control pushrod is moving absolutely freely in its guides yes?

Have you checked the hub and everything on the tail assembly, they have a knack to come loose on the Raptors this I know from experience. Check that everything's still secured where it should be.

When you unlink the tail pushrod on the servo's side you should be able the control the pitch on the tail rotor absolutely freely, if there's ANY friction fix it, something's off.

Your gyro's mounting, the gyro is not touching anything at all. The wire is not under strain. You used a good soft double sided tape to mount it? It's not close to any RF noise like servos and things?

I will have to consult my 770's manual quickly tonight before we talk setup. I haven't touched mine for more than a year so not exactly sure what I set where again. But ya first elaborate on the problem for me and let's go over the basics.

[Gavin2407]

Hi Spacey

Rechecked everything last night as I also thought tail not setup machanically correct but yes blades are running in correct direction (anti clockwise when looking from right side of heli) and blades on the correct way. I converted from a 30 V2 to a 50 so kept the whole tail assembly as it was on the 30, just thought I maybe twisted the belt wrong way around. The motor I'm running is a TT50 Pro (I know it's crap but it will have to do for now) got it running smooth but very rich as it is new and don't want to fry it like I did my TT39 that was "professionally" setup. The tail control rod has no binding and moves freely in the guides, only thing I did find was tail blades were to tight in the blade grips (I tend to rather tighten rather than having something loose, those buggers turn at an unbelievable rate) loosened them a bit and with my rudder servo sitting up front I have the long tail pitch pushrod it was smooth one way but slightly twisting the other so sorted that out. Gyro is sitting behind the mainshaft above the tail case of the main frame and using supplied tape it is as per manual. heli has slight vibration during idle but is smooth once off the ground, responds very.

The main issue I'm having trouble with is the on my 30 I could switch between HH and rate mode without the heli doing anything funny, Yes I know in rate mode the heli will weathervane into the wind during hover but will "follow" heli during forward flight and HH the tail should stay put no matter what until a rudder command is given but now on the 50 it doesn't just weathervane in rate mode, it spin around completely very slowly to the left during hover but jumps right when doing a climbout. If I sort rate mode out then HH is out and doen't hold the tail very well. sorting HH will make things worse in rate mode.

Don't know if I'm just being silly about this but just can't understand why on the 30 it "worked" well in both mode but now on a 50 I should settle for either of the two but can't have both. I would guess most people will fly in HH mode anyway.

After checking the whole heli over last night, took her for a spin in the back yard and tried different gain rates, getting better but still not right. don't want to just sort out the syptoms and not the causes of the problems.

[spacey]

Hi Gavin,

Ok cool if everything's "OK" mechanically we're getting somewhere. The motor running rich and rough will definitely cause all sorts of headaches for you as well, the gyro gets bombarded with vibrations due to this, just like a motor running too lean and would cause it to drift. The modern day gyros have awfully sensitive sensors in them which doesn't like this sort of thing so getting the heli smooth and running in top form before worrying too much about anything else is probably the correct answer for the moment.

Either way, to go further on the drift. The 770 works different than other gyros in that you need to "calibrate" the servo with the gyro initially. You need to tell the gyro where the centre point of the servo is. To do this make sure you have absolutely no trims dialed into the rudder/tail on any of the flightmodes whatsoever. Switch everything on in Heading Hold on the bench and let the gyro do it's thing for a few seconds, observe the tail rotor. If the tail rotor now persists in drifting in a certain direction even very very slowly the centre of the servo is off. Adjust the Sub Trim on the radio programming (Not the trim under the stick itself, never touch this one and leave it dead centre) for the tail rotor untill the servo stands absolutely still. Wiggle the stick around and observe the tail rotor again, keep asjusting the trim untill it stands completely still. I could maybe advise you drop the sub trim step on the TX to 1 point so you can really fine tune these things. The tail rotor should stand completely still on the bench if the sub trim is adjusted properly, from my experience the sub trim values needed to accomplish this is never more than 10points, usually around 3~5. Be sure to adjust the sub trim on the programming as this will adjust the trim in all flightmodes which is what you want.

Now you might find that if you start the motor and such the tail starts drifting again in HH, vibrations coming into play. You CAN adjust the subtrim again ever so slightly to fix this drift and you are welcome to adjust the subtrim if the heli is in a hover in HH to get the tail to stop drifting. Just don't use the trim under the stick ever, land and adjust the sub trim 1 point at a time untill it stands still. If you have to adjust it in this way you can be assured something's wrong on the model motor or vibrations wise.

Right when everything is sorted in HH you can now switch to rate mode on the ground and lift up into a hover again. If the tail now drifts you need to mechanically adjust the pushrod length linking the tail rotor and tail servo. Rate mode is all about mechanical trim so you physically need to adjust the link on the tail rotor or by the servo in front adjusting the length of the pushrod and essentially the trim of the tail rotor. Fly, adjust a little and fly again. That's the only way.

That should fix the trim on both HH and Rate mode.

If the tail's not holding well in either of the flightmodes you need to adjust the gain settings on the radio for the respective modes. I never use rate mode other than trimming the tailrotor so I'm not too experienced in actually flying with it and adjusting gain in it. But I suspect you will have the nose going all over the place when making sudden pitch changes especially if the tail rotor setup is not very effective. Adjust the gains up untill you get a tail wag in fast forward flight and then back them off a little again (Maybe 5 points) and re-test. This is about the simplest way to get the most out of any gyro. Beware gain settings could change as you start flying backwards and inverted backwards, heck even in just normal inverted flight due to the different airflows experienced by the tail rotor, so you might need to fine tune again later.

[Gavin2407]

Hi Spacey

thanks stax for all the info and advice. been chatting with BarracudaHockey on RCUniverse also and can't wait to test out everything this weekend. it is nice to know that there are guys like you that don't let their skill's go to the head and are prepared to help guy's like me. us beginners need all the help we can get and it is through forums like this that we can ask questions no matter how silly it may sound without being shot down. once again thank you.

[spacey]

No probs Gavin, give me a call if you're still stuck over the weekend and out at the field. Easy to troubleshoot then also. 082 332 0045