Help!! E720 Rotor head wobble

[Hawk208]

Hello, I had a brand new E720 and just did a test spool up. (Blades and Flybars are not attached) Then, I noticed that the rotor head doesn't run true at low speed. (I could clearly see the head button wobble.)
I have to pump the throttle to around 70% to get the wobble completely disappear.
What I have done so far is:

1. Disassemble the entire head and test run it with head block only. (still wobble)
2. Test run with tail boom taken off. (still wobble)
3. Test run with main shaft only. It comes to the tricky part. The main shaft will actually shake for a second or two at spool up and then run completely true after that.

I wonder if any of you had experienced this kind of stuff before. This bird is new, I don't think the main shaft is bent (15mm!!!) and I don't want to start swapping parts blindness (parts for G4 ain't cheap.)
I will try to make a video for it later.
Thanks a lot.

[tshelby73]

Odd. Bearing blocks in right way. Maybe bearing came out of block?

[Hawk208]

Yeah, the bearing block is right. No play for main shaft at all. I might try call thunder tiger for help.

[phillhague]

Hawk, is it actually wobbling or might it be the torque and vibration from the motor as it starts up making it appear to wobble, if it is it could be a gear mesh problem.

[Hawk208]

Originally Posted by phillhague

Hawk, is it actually wobbling or might it be the torque and vibration from the motor as it starts up making it appear to wobble, if it is it could be a gear mesh problem.

Hi, I adjust the gear mesh using the two plastic bag and print paper method. The result seems no difference. It looks like some kind of low speed wobble, but I can't really show it in a video. Because the jive won't maintain that RPM.
I found another thing about the head block. There is a black ring with two pin mounted under the head block. (I don't know what that called) When installed firmly, I could see a hair line gap between the head block and the black ring on one side, but there is no gap(light won't went through) on the other side. Does it mean the head block is tilted? I haven't heard back from the service dept yet.

[phillhague]

Think the part you mentioned is called a phase ring, it provides drive to the washout base and swash ( you got a manual ? LOL ). Just noticed you are talking about a flybarred heli, both mine are flybarless but the head block mounting is the same idea on both types.
Just been looking at the first post and you say the mainshaft shakes for a second or two at spool up, if the shaft is a good sliding fit in the bearings there's no way it can shake unless the bearings are faulty ( very unlikely ). I assume that there is no excess up and down play in the mainshaft ( just give it a good hard pull and push vertically to check that ). Just checked both mine and there is a few thousands of an inch up and down play, just enough to feel it. Also check the mainshaft is all the way through the bottom bearing with just over 1mm protruding through it.
Other than that it sounds a bit like the motor is not spooling up smoothly and is stuttering between forwards and reverse direction causing harsh vibration until it gets up to a RPM that it is happy with, only really seen this at low RPM's though unless you have a poorly soldered connection on the motor /ESC wires.
Only other way to be sure is to pull the mainshaft and headblock out as one unit and put it in a lathe, then spin it up and see how it looks. If it's all running true then there's not much wrong and you will have to check bearings and blocks for problems. Or you can check if the mainsahft is running true on it's own by rolling it along a kitchen worktop or similar flat surface.
I see what you mean with gear mesh, my method is to shove the gears into mesh just slightly hard, back motor off a fraction then rotate maingear by hand to find the tight spot, then adjust motor to give the very slightest amount of backlash by feel at the tight spot. Keep us posted as I and no doubt others are interested in what the problem eventually turns out to be.

[Hawk208]

Phill, Thank you so much for your long detailed reply. I am very appreciated. I just went home for Christmas and internet is terrible. I already asked HRP for a new main shaft and I am waiting for the reply. However, I am suspecting the head block that is defective. Everything will be super busy when I went back to school, but I will keep it updated. Anyway, Happy New Year!!! (to everyone)

[Don S]

Did you spin up with no head block attached, watching the end of the main shaft for wobble?

[Hawk208]

Originally Posted by Don S

Did you spin up with no head block attached, watching the end of the main shaft for wobble?

It wobbles as well. but only at the very end of the soft start process and last a split of second. Again, Jive won't maintain that RPM. So I can't have a good observation.
You think it's a bad main shaft? but 15mm, it shouldn't bent.

[Don S]

Pull the shaft and roll in on a flat table, or piece of glass, etc. See if it rolls true.

[Hawk208]

You're right Don, brand new main shaft is bent.
It's over a year now, not sure if I could still have it replaced for free.

[Don S]

Bummer dude. At least you determined what the problem was.