New buid Trex 700 wobble

[DaOne]

This one has me baffled. Not even sure what to do next. I have a new 700 that I am breaking in. I am not using the gov while I do this. I can spool up and get into a hover just fine. No wobbles. As soon as the engine catches up to speed I get a oscillation around the main shaft. the skids start shaking. I figured ok the head speed is too low so i ramped it way up and it gets worse. I figured i had a bent main shaft. Nope. So I checked the spindle, thrust bearings, re-greased the dampeners,checked the balance of the head without blades, checked the blade weight and everything is perfectly fine. Not sure what to do next? Anywhere else I should be looking other than the head?

[Heligunner60]

RU running a Gov?

[Heligunner60]

What blades/motor? Is it running rich?

[DaOne]

Yes I have a gov but it is off. I am breaking it in so yes it is rich. I am only on the 3rd tank.

[asdf1234]

sounds like low headspeed?

[DaOne]

sounds like low headspeed?

Well here is the weird part... it gets worse with higher head speed and goes away at a very low speed.

[haq0901]

Blades???

[jwilkens]

Did you check your paddles, a few people had issues with paddle comming loose.

[cbdane]

You might want to rule out a machining error in the head block. Something could have slipped while it was in the CNC mill.

[DaOne]

right now i am leaning to a headblock/dampener issue or blades. Everything else check out. Whole head was balance checked on a highpoint and was dead on. This includes the paddles. I borrows my buddies 700 to start swapping parts to find out where it is. Blades i am running are SABs. The white / black 710s.

[rg686]

This one has me baffled. Not even sure what to do next. I have a new 700 that I am breaking in. I am not using the gov while I do this. I can spool up and get into a hover just fine. No wobbles. As soon as the engine catches up to speed I get a oscillation around the main shaft. the skids start shaking. I figured ok the head speed is too low so i ramped it way up and it gets worse. I figured i had a bent main shaft. Nope. So I checked the spindle, thrust bearings, re-greased the dampeners,checked the balance of the head without blades, checked the blade weight and everything is perfectly fine. Not sure what to do next? Anywhere else I should be looking other than the head?
I've seen similar problem before. It turn out the problem was that the dampeners are not all the way in the head block because the feathering shaft plastic sleeve is not seated correctly.

[DaOne]

Ok I am now really at a loss. I changed the blades. Problem solved. Here is the crazy part... the SABs that are giving me the issue are perfectly the same weight and the cg is spot on.

[Dr.VanNostrin]

They may weigh the same but their pivot points are off.

Any rotational vibration issue is a pivot balance/weight diff problem.

Check weight. Check dist/pivot. I.e. blade grip bolt center to end of blade.

In other words; both rotational parts need to weigh the same. Both rotational parts need to pivot at the same point. Otherwise one will be longer than the other/thus weighing more at its pivot point center. Yes?

Dr.V

[DaOne]

They may weigh the same but their pivot points are off.

Any rotational vibration issue is a pivot balance/weight diff problem.

Check weight. Check dist/pivot. I.e. blade grip bolt center to end of blade.

In other words; both rotational parts need to weigh the same. Both rotational parts need to pivot at the same point. Otherwise one will be longer than the other/thus weighing more at its pivot point center. Yes?

Dr.V
I thought that was called the CG.. its dead on.