Tail Wag Cures

[Steve Joblin]

Seems that every few days a new T-REX 250 owner completes his (or her) build and prepares themselves for the maiden flight of their new heli.... only to find out that once the heli spools up and settles into a hover, the tail wags back and forth Whilst some may say that it is just the sign of a happy 250 (like a dog that sees his master), most are disapointed and land their heli in frustration. Some may find a quick cure to TWS (Tail Wag Syndrome), others seem to need weeks or months to find a cure, and there are an unlucky few that never get better. I was one of those folks that had a bad case of TWS and it lasted for many, many weeks until my 250 was cured. In the end, I was never really cured... I just found a solution that masked my syptoms.

Here is the journey I took to find a cure... if others have other ideas or suggestions, please add them!

1. Inspect, re-inspect, then double check that there is no binding in the tail mechanism

2. Position the servo ball on tail servo arm to 4.5mm (or even closer) from the center.

3. Install a Kevlar Belt (see my video showing how a belt can be damaged, but not broken)

4. Try different size tail rotor blades:

• 42mm Straight Cut Blades
• 40mm Batwing Blades
• 37mm Batwing Blades
• 35mm Straight Cut Blades (home made by simply cutting a blade down to size)
• 32mm Straight Cut Blades (home made by simply cutting a blade down to size)

5. Install a CF Carbon pushrod (a fun project that you can make your own)... the idea is that you remove any friction in the rod guides.

6. CF Boom (maybe there is a slight bend in the aluminum boom that is affecting things?)

7. Install a Metal Tail Rotor Control Arm

8. Remount the Gyro on two layers of foam tape

9. Set the Gyro Delay to 100%

10. Change the ESC BEC voltage to 5.0

11. Change the GP780 Gyro Analog/Digital Servo Setting from "DS" to "AS"

[smccrory]

I've heard that Spartain Quark and JR 3500G users should follow instructions to set the tail servo ball link to 5.5-6.0 mm and probably no closer, so you might want to add that caveat.

Of course vibes of all sort can play a big part. On other models, once I've resolved head runout, bent shafts, etc. I've increased head speeds and set up gov mode to get off of resonant frequencies.

[exit44rc]

I'm running a Quark/3500 setup and 6.0mm is the sweet spot for me on the tail servo ball link position. I also went into the software and reduced the stop gains. They are currently set at 75 but it's not quite right. I'm thinking that 80-85 is going to be my number there.

[rickyg]

Originally Posted by Steve Joblin

10. Change the ESC BEC voltage to 5.0
\

+1 on that. I've done that on two separate 250s (three counting mine) and that seemed to pretty much fix everything. It even seemed to make it less twitchy in the cycle too.

Ricky

[BorgeBorge]

Originally Posted by Steve Joblin

10. Change the ESC BEC voltage to 5.0

Change from what?

[Steve Joblin]

Originally Posted by Konrad78

Change from what?

There are three settings... 5.0, 5.5, and 6.0 The default is 5.5 volts.

The lower the voltage, the slower the servo motors move.

[Xdrive]

Instead of changing the voltage, wouldn't it be the same to increase the delay on the gyro?

[Steve Joblin]

two different things (I think!). one deals with how long before it responds, the other is how fast the response takes. Again, this is my understanding, but I very easily could be wrong so other will need to verify my statement.

[Xdrive]

What about increasing the expo? I just don't get why increasing or decreasing the voltage will do anything.

[Steve Joblin]

inside the servo is a motor. the more voltage, the faster the motor will spin. the faster the motor spins, the sooner the servo arm reaches it's destination.

[Ozz58]

Originally Posted by Xdrive

What about increasing the expo? I just don't get why increasing or decreasing the voltage will do anything.

This sticky is about wag. expo will not do anything to fix wag, voltage and delay and the other things Steve posted will address a wag issue.

There have been many fixes, too bad they are NOT all the same. This is what make the wag such a big problem. One fix for someone will not fix it for someone else.

Even after a crash with the same set-up I would get a wag back, it would take some time to fix it, and to tell the truth sometimes I don't know what fixed it.

Gotta love the 250,

Craig

[rccrazydoc]

you are absolutely right buddy...i too have been struggling with a wag since a crash about a month ago...tried every possible thing and right going back to setting the tail up all over again with bob's videos as a guide..! probably its just a matter of time and trial and error....just gotta hang in there and never give up!

[Steve Joblin]

I just saw that Andrew McGregor posted in another forum this idea to improving tail control:

So, I've been meaning to post this...

I got a large improvement in tail behaviour on my 250 by setting the travel adjust on my X9303 to 125% and the throttle curve to 100%, using governor on a stock ESC. I do have a Hyperion DS11 and Futaba 401 gyro on there... but they did not make any improvement before fiddling with the throttle channel, and I mean to swap back to the stock gyro and servo when I get a chance, to see what happens.

So, if you still have slightly twitchy tail behaviour and you're using a Spektrum TX, try the throttle travel adjust to 125 and curve to 100 thing, and see what happens.

[johnnychimpo]

Futaba gy520 fixed my wag.

[rccrazydoc]

agony,agony,agony! the trex250 wag is killing me! there isn't a single solution that i dint try!....sometimes the wag is there and sometimes not!....though am a newbie(about 4 months into this hobby), i've spent 2 months tweaking this crap! i just dont get it... one minute theres a violent wag and the next minute its not there!and sometimes a slow wag! am confident that the gp780 is not the problem!the only things not tried are-
-new gyro
-microheli tail
-bigger servo
guys pleeeeaaassseee help me out to get this damn thing to fly neat! can't afford a new servo or gyro right now....though i have a new hk 401 lying around' which i feel is going to make the heli heavier...desperately looking for solutions! jr290g/gp780 on the tail
If the wag isnt continuous can it be an electrical/esc issue? or is it mechanical?

[pitchp]

it was working nicely before the crash? if it was, then no need for a new gyro. It can be electrical/mechanical. Check for a jittery cyclic servo. you will have to take off the blades(main+tail), then power it up, give it some throttle, check all cyclic servos for jitters.

[rccrazydoc]

had just about 4 hovers before the crash! was on training gear...so difficult to say if the wag was absolutely not there..no noticeable wag though ...when i power on the left cyclic has started to jitter since last week..! but my wag has been there since before! tried different th curves too...right now on trimmed kbdd blades and th curve 0-55-90-90-90..whenever i play around with the th curve the wag disappears but appears suddenly later! just cant decide on one setting!

[Dr.Chopper]

beast x fixed my wag and made it fly 10 times better

[Steve Joblin]

You using a Kevlar Tail Belt?

[sparky66]

Originally Posted by Dr.Chopper

beast x fixed my wag and made it fly 10 times better

What servo are you using and what is your ball distance from center? After my last crash I have a wag and I can't find the cause? What setting are you running in the beastx?