View Full Version : EP8 wags its tail - Any ideas?

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02-28-2010, 06:28 PM
From day 1, My EP8 has had a tail wag I can not tame.
First off, a basic question: Does the EP8 use leading or trailing edge control on the tail?
I have tried both with leading edge control seeming to work better.

My equipment and details:
Radio is a DX7 with Gyro gain on GEAR channel.
Gyro is a GY401 - Delay=0, Travel just under 100
Very little drift in gain mode so centering does not seem to be a problem.
Tail servo is a Hyperion - DS13ACB
The GY401 is in digital mode (tried both modes with no difference noticed)
The tail wags in both heading hold and rate modes..
Setting the gyro gain on the DX7 to +30 (heading hold mode) cuts back on the wag but it is still present.
More gain = more aggravated wag.

Head seems a bit tight but seems vibration free once spun up.
Heli has never been crashed.

Thanks for any advice!

03-01-2010, 01:10 AM
I had a similar problem early on while hovering and determined that my head speed was too low. What is your head speed?

Leading edge control is best for the 8's tail rotor.

03-02-2010, 12:16 AM
Thank you Henry, I think you may be correct.
I don't have a tach but using the head speed calculator, I think I am only running about 1600 RPM in hover (not in idle up).
I believe that is too slow and something more like 1800-1900 is desired.
Do you agree?

03-02-2010, 12:33 AM
Absolutely. 1600 is where I was experiencing the wag. Another couple hundred rpm should wipe it out! Let us know how you get along...

03-02-2010, 12:37 AM
Thanks again Henry. I will post an update once I get to fly again.

03-02-2010, 09:44 PM
Paul, I have had to fix that problem before. What I do is first I make sure the complete linkage is working freely. I unhook the linkage at the servo arm, and i take my fingers and move if just a little bit back and forth. It should move very freely and not bind at any point. If it does not move freely, I unhook the plastic links from the balls. Now move the linkage, and find any part that does not move freely. Use only thin 3in1 machine oil or such on the t/r shaft. Then I snap one of the links back on. If it does not work freely, either buy one of those tools to make it a little bigger or take a pivot ball and mark it up with a set of pliers and put it in an electric drill and turn it very slowly and put the link on it and move it around so to enlarge the inside, Only just a little bit.
Your t/r blades should pivot with just a little resistance in the blade grips. Make them both feel the same. They have to be free to lead and lag at the different speeds of the rotor.


03-03-2010, 12:41 AM
Harold, thank you for the great advice. Once I get a chance, I will carefully check the operation of the tail and also increase the head speed as Henry suggested. The EP8 went together very easily but the ball links are a bit tight but not to the point where I knew I had to use the link sizer. I figured after a few flights it would loosen up a bit.
I will report back and hope to snap a picture as we need "Show me your QJ thread".

03-03-2010, 09:26 AM
That's good. We will get it right, one way or the other. If it does not work freely, make you a reemer tool out of a pivot ball and just use it a very little at the time, moving it all directions as you turn the drill on slow.


03-05-2010, 12:09 AM
Hey PAS, how's your progress?

03-05-2010, 12:15 AM
Thanks for asking Henry but unfortunately I work 10-12 hours a day.
Add the family to that and my R/C time is very limited.
I hope to get some time in this weekend.
I was thinking that I should probably get a new pinion to speed up the head a bit.
The motor shaft if 5mm and I currently use a 12 tooth and think I should go to 13.
Do you know the where I can get the correct pinion to mesh with the EP8 main?

03-05-2010, 12:43 AM
Contact Charles at Helicopter Hobbies. He should have some on hand. You might want to consider a 14-17 tooth gears. I'm happy with the 17 tooth...

03-06-2010, 04:16 PM
Thank you Henry and Harold, you made my day!

First, I increased the head speed to approximately 1900 RPM but still had some tail wag.
I decided to give the tail another look over as Harold advised.
Everything seemed smooth but the ball links attached to the tail grips were a on the tight side.
Using the ball link sizer a did just a couple of turns on each link and they did snap on a little easier.
To my amazement, the wag DISAPPEARED!!!
I was able to crank the gyro gain way up with absolutely no tail wag!!

As far as getting another pinion, I don't think I should go more than a 13 tooth.
I am running 6 cells with a 1030Kv motor (85% efficient) which gives a maximum head speed of 2206 RPM.
According to the head speed calculator, I will exceed 2400 RPM (2574 RPM) on a full battery if I go to a 14 tooth pinion.
For now a 12 tooth will probably be fine as long as I keep the throttle @ 80% or better.

03-06-2010, 04:41 PM
Glad to hear you got tit gone! Hope you are using carbon fiber blades!

03-06-2010, 09:36 PM
I have both wood and carbon fiber (just purchased from Charles).
I was hoping wood blades would be OK to about 2000RPM.
Do you think I am pushing it?

03-08-2010, 09:02 AM
Good work guys! If you tail rotor ever moves or jumps around, check the tension of the tail belt.
If it is the 400mm wood blades for the EP8 from Japan, you do not have to worry, i have seen them run 2200 for years and we never had one to destroy a heli.

03-14-2010, 06:59 PM
A faster servo for the tail will also help.

That servo is 0.16 at 4.8 volts. I run an S9254, which is 0.06 second.

03-15-2010, 09:34 AM
Hey Terry,

That is a good servo. I am glad to see you helping us out, I think you have a good flying EX. Is that the servo that comes with a 401 ?


03-15-2010, 01:26 PM
Yeah, that is the standard size tail servo that comes with some 401 kits. You can also get the 401 with a min servo (S9650).

I run the 401 with S9254 on my EP8, Hurricane 550 and Pantera Nitro. I run the JR 770 3D with 8900G on my Vibe and Bergen Intrepid Gasser.

03-15-2010, 05:09 PM
I knew you had all the good stuff! I did get the latest JR 500 size Gyro from Charles last month. It has been great in this wind lately.

Charles has a new battery tray coming for the EX.


03-27-2010, 02:43 AM
I just swapped the Hyperion servo in the tail for a Hitec HSG-5084 (over 2X faster) and the tail seems very locked in with no wag.

03-27-2010, 07:59 AM
That's good. I am going to have to take a look at that servo, I believe that is one of the new releases. It sounds like you have got it working better and have the length of the servo arm and gain dialed in. What RPM are you hovering? Do you have a hover or normal mode and an Idleup 1 Mode?


03-28-2010, 12:01 AM
I don't have a optical tach but I do have an iphone so I purchased the Helitach application that is being talked about on HeliFreak. In normal mode I was using an accelerated throttle curve that would have the throttle at 80% with the stick at the mid point and 0 degree pitch. In normal mode, from mid stick up, I have a linear throttle and pitch curve. While in a hover, the Helitach was reading approximately 2200 RPM. I slowed it down a bit so in normal mode hover was 2000 RPM and that seems about right for me.

I am still having one more bit of frustration. I am unable to get more that about +/-5 degrees of pitch change on the elevator. With the aileron +/-8 degress of pitch change is easily possible. The elevator just will not move that much. I feel like I need to adjust some of the swash/travel settings (Dx7 radio) but I spent time on this today with no luck.

Any ideas?

03-28-2010, 12:22 AM
Is that helitach app any good? Is it easy to use? Does it use an algorythm to determine head speed or what? Sorry...I have run out of questions!:YeaBaby:

03-28-2010, 09:22 AM
Your hovering setup looks good. I always do the final adjusting on how the heli hovers and feels moving the sticks. I have been taught to make each movement of the stick to be and feel about the same, or linear. Most people do not run more than 6 degrees on the elevator for regular flying.
Yes, you can increase it with the swashplate travel settings. When you increase the elevator, the cyclic changes in the same porportion.
Hover the heli and get it where it responds the way you want it to respond on the feel of the sticks, and make elevator and cyclic movements have the same effect making the heli move. That is what I have been taught.


03-28-2010, 10:19 PM
Henry - The iphone application is very easy to use. The only bad part is putting an expensive phone on the ground while spinning up and hovering the helicopter. Not a big deal with electrics but I would never use this for a nitro. There is a big thread here on Helifreak with a lot more information if you are interested:

Harold - I am having a problem getting 6 degress of elevator. I just cant go past 5 degress without some binding. If you know there is no issue with QJ8 getting 6 or more degrees of elevator then I must have something not quite correct in my setup or radio settings. I will keep looking.