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T-REX 500
Trex 500 Tail Bounce
Posted by Slowpoke on 03-13-2017 10:41 AM:
It is common knowledge that most Trex 500's need to be run at a high headspeed to keep the tail from bouncing up and down.

I've searched out many threads in many forums about this issue, and the answer is always "raise the headspeed".

I have 3 500s and they all have this issue. None of my other sized Trex helis have this issue - 10 helis from 450s to 800s.

What I'm trying to figure out is WHY? What is different in the 500? They seem to have the same basic design as the other Trex models. All of my 500s are in new condition. I've balanced the main and tail blades and checked the balance of the head block and blade grips. All of the rotating parts like torque tubes and tail and main shafts have been checked and replaced with brand new parts. I've also tried using more than one torque tube bearing in the boom.

They all have 1600KV motors - 1 Scorpion, two different Align motors, 13T pinions and 162T main gears. According to Mr. Mels HS calculator, this should be giving me close to a 3000 HS.

I'm not talking about side to side tail WAG. This is an up and down BOUNCE. The tail holds very well side to side and is very locked in, so suggestions about gyro gain and the like don't seem to be an answer.

Even running at the max headspeed I can, there is still a little bit of bounce. I'm a sport flyer, don't do 3D, so I'd like to run a more conservative headspeed for flight time like I do on my other helis.

What is different about the 500?

Posted by Pistol Pete on 03-13-2017 03:36 PM:
Dominator 500
Have you balanced blades and grips as a unit versus individually?

I fly it with 4, 5 and 6 cells and never at full speed. Like you, I fly sport but I dont have a bounce. My shortest flight is 8 minutes.

Perhaps an FBL setting?

~~Enjoying the hobby one flight at a time~~

Posted by BeltFedBrowning on 03-13-2017 04:12 PM:
An alternative to raising the headspeed is changing to softer dampeners or heavier blades. Are your birds old enough to have the feathering shaft sleeve? It makes the head stiffer. I recommend removing the sleeve and installing grey dampeners.
Posted by Slowpoke on 03-13-2017 05:01 PM:
PP: no, not as a unit. I will try to figure out a way to do this.

BFB: I was not aware that the sleeve contributed to the stiffness of the head unit. All 3 of my 500s use them. I have ordered some of the grey dampers this morning.
Posted by iyoy on 03-13-2017 11:50 PM:
FBL unit
What are you using? I have the Microbeast Plus and had the same problem initially. Turned out to be wrong settings for the servos.


Posted by Slowpoke on 03-14-2017 03:05 AM:
I'm using mini vbars. all the helis have the DFC head and swash plates.
Posted by u8mydog on 03-14-2017 03:27 AM:
I have DFC and use Brain/Icon. I don't have tail bounce up and down.

I did have a weird wag but found a missing step washer in tail control arm so there was slight binding (purchased it used).


Posted by Slowpoke on 03-20-2017 12:10 AM:
Ok, got the grey dampers today. Just on the bench, I could feel the difference in the stiffness at the head.

In the air, it did help reduce the bounce, but there is still a little there.

I can live with it, but wondering about removing the feathering shaft sleeve also. There is a lot more flex without it.

Is it safe to run both the grey dampers and no sleeve?

Posted by Heli Fanatix on 03-20-2017 05:11 PM:
Check your Torque Tube bearings
- find the mid point
- than go 5mm either side
- the point is not to put the bearing on the torque tube exactly in the middle. It creates a sine wave that's causing your up & down oscillation

- Scott

Posted by Slowpoke on 03-20-2017 07:32 PM:
In 500#1 I have the bearing 1" ahead of center, in 500#2 1" behind center and in 500#3 I have 2 bearings installed at uneven places. All have the same bounce.

The grey dampers definitely helped. I'm going to remove the sleeve on one of them, cross my fingers and see if that takes the remaining bounce out and hope I don't get a boom strike.

Posted by Heli Fanatix on 03-21-2017 03:31 AM:
IC .. if that is the case
- run the softest dampeners you can get (use polyurethane lubricant on spindle)
- balance the main blades along with the entire main shaft & rotor head
- try various HS: 2600 or more

- Scott

Posted by balsabasher on 03-21-2017 05:15 AM:
I had a 500 Pro FBL with a Skookum 540 that did that. I found a different mounting tape under the controller solved the bounce.

Blades; what goes around, comes around!

Posted by BeltFedBrowning on 03-21-2017 01:01 PM:
I have good luck with silicone lubricant on the dampers as well.
Posted by JuanRodriguez on 03-21-2017 01:05 PM:
What's urethane lubricant ? Never heard of it . I've heard of polyurethane bushings.....
Silicone grease or white lithium grease is what I use ...

Been there, done that and old enough to know better.....

Posted by Heli Fanatix on 03-22-2017 06:41 AM:
You know what we mean Juan .....

- Scott

Posted by JuanRodriguez on 03-22-2017 01:12 PM:

You are the only one that used that terminology...... no, I didn't know what YOU meant and that's why I asked....I thought that perhaps there was something new out there that I was not aware of.....

But apparently it was just a misuse of terminology on your part......

Been there, done that and old enough to know better.....

Posted by Heli Fanatix on 03-22-2017 04:51 PM:

Apparently it was not what you wanted to hear, but it was enough to let you and a others know what I'm referring to.

Go back and check all my posts ...I am one of the more technical contributor.

If you want to contribute, maybe you should of mentioned about the silicone grease first instead of making it a point to correct people whom is trying to help figure out the problem at hand.

"Poly-Urethane" when dry can squeal & create friction. If left uncheck, can result in heat and worsen the situation. If we find some type of lubricant, the effects can be seen almost immediately. If that solved the problem, we can see that lubrication is the problem.

If you store a heli and the blades are folded for a long time, the heli might wobble when flown again b/c of the flat spots in the O-Rings

This may not be the case, but it's good information to know

Silicone Grease is the most ideal medium, but various options can be used in this hobby as the lubrication to pin the problem. One of the many options can be:
- Align one way grease
- triflow grease
- heck, even vegetable oil (if in a pinch)
- pretty much any lubricant, reason for keeping the term general

Didn't want OP to run out and get silicone grease when they might have something around that might work.

- Scott

Posted by JuanRodriguez on 03-23-2017 02:13 AM:
Scott ,

Not what I wanted to hear ?? Again , don't know what you mean by that ..... if you are as technically inclined as you claim then you should use the correct technical terms for something you are recommending.....

Anyone flying helis should have silicone grease in their "tool box" ......not expensive in the scope of things......

And if you read my posts you'll see that I contribute plenty.....

Been there, done that and old enough to know better.....

Posted by DennisH on 03-23-2017 03:42 AM:
Well, . . . . I have been following this thread and find it very informative.

As you see, I have not posted anything, I am reading only, and learning.

JuanRodriguez & Heli Fanatix: I find both of you contribute to this website and both bring valuable information to all members, which is very much appreciated.

I don't think I need to state anything else.

I am highly interested in this thread and hopefully I will learn something I can apply to my Helicopters.

FWIW, this is not a suggestion, only my personal opinion, I like Silicone lubes/grease, plus I have special lubes made with graphite (high temp applications) I use on certain areas.

I don't like any lubes that are thick and can dry out. I would rather lube more often than use these type lubes.

JMO, Dennis, and let's move forward.
Posted by Heli Fanatix on 03-23-2017 04:53 AM:
This is what I learned Dennis:

Give a wiseman an advice...they will thank you

Give a fool an advice...they will yell and criticize you!!!

- Scott

Posted by DennisH on 03-27-2017 12:01 PM:
This is what I learned Dennis:
Give a wiseman an advice...they will thank you
Give a fool an advice...they will yell and criticize you!!!
Thanks, Dennis
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