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Goblin 700 › Wobble at lower head speed
08-20-2014 09:30 PM  3 years agoPost 1
crunch

rrApprentice

Peterborough, England

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Hi guys
I know there is a lot of people running lower head speeds now on the goblin 700, I have the hps head on mine but can't stop it wobbling when I running say 1550 head speed, I re geared my motor to run lower head speed so I get the longer flights which works well apart from the low head speed wobble. I've seen the goblins running 1100 head speed with no wobble.
I've tried running blades looser but nothing. I've removed all the preload in the head apart from the brass shims. I've moved batterys back and forward but didn't work although it got a lot worse when I moved battery's forward. It could be a setting in my vbar that's causing it but I don't know.
I've come to goblin forum as it's a goblin issue, I know there is a low head speed section but I would like information from goblin owners if possible.
Regards Paul

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09-27-2014 07:15 AM  3 years agoPost 2
airplaneman777

rrNovice

Houston, TX

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I have the same problem running a 770 at 1600....haven't found a fix yet.

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09-27-2014 11:04 PM  3 years agoPost 3
crunch

rrApprentice

Peterborough, England

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I tried all different head speed anything under 1650 just wobbles tried different dampers as well.
Not sure why some can run low head speed and others can't. I have the HPS head and DFC head.
I've tried reducing the preload on the head as well still wobbled.

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09-28-2014 01:53 AM  3 years agoPost 4
Retired2011

rrElite Veteran

Lee's Summit, MO

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This is NOT a Goblin only issue...wish I could figure it out.
Maybe post in the main forum to get more opinions.

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09-28-2014 02:15 AM  3 years agoPost 5
AWittleWabbit

rrElite Veteran

O.C., CA

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Have you tried different blades?

Heavier or lighter?

Dampers lubed?

Is the damping really as soft as you can go?

I played with the above indirectly on my old Concept 30. I was running the head on the slow side inadvertently.

These are generic questions. I have no experience with the gobby, other than I want one.

Heli-itis sufferer.

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09-28-2014 02:19 AM  3 years agoPost 6
AWittleWabbit

rrElite Veteran

O.C., CA

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Almost forgot
Low cyclic gain?

Heli-itis sufferer.

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09-28-2014 03:02 AM  3 years agoPost 7
Retired2011

rrElite Veteran

Lee's Summit, MO

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I have tried all of the above on my Logo 400...cyclic gain from 40 to 120 on a V bar.
It does change a little with different blades, but doesn't go away.
I just have to stay above ~ 1800

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09-28-2014 07:37 PM  3 years agoPost 8
crunch

rrApprentice

Peterborough, England

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I tried altering my gain on the Vbar. I did try soft dampers and they were greased up so they had plenty of movement. I didn't try different blade.

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09-28-2014 11:35 PM  3 years agoPost 9
AWittleWabbit

rrElite Veteran

O.C., CA

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I would look at the blade weights and maybe experiment there. Hopefully some who has done this on your exact model will speak up.

I would like to know more about why slow speed wobbles happen myself.

BTW

I find Curtis blades tend to be the heaviest in a given size. Hopefully you can borrow a set(s) from friends to experiment with. I can see this getting expensive.

Heli-itis sufferer.

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09-29-2014 01:05 AM  3 years agoPost 10
Retired2011

rrElite Veteran

Lee's Summit, MO

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I tried a set of Reveloutions today, no difference...I'll just fly my little one a little faster.

Maybe I'll look into some CY's.

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10-07-2014 02:19 AM  3 years agoPost 11
JKP35P

rrNovice

savannah, GA

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i had this issue with a goblin 570 this weekend and the results were a little embarrassing i must say but the fix for my helicopter was main shaft was shimmed too tight i had both shims in the main shaft resulting in no play i took the thinnest shim out allowing very little play up and down on the main shaft and a little triflow oil on the swash and main
shaft fixed my helicopter hope this helps !

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10-07-2014 03:04 AM  3 years agoPost 12
airplaneman777

rrNovice

Houston, TX

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What shim on the main shaft are you talking about? Thanks for the help btw!

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10-07-2014 04:09 AM  3 years agoPost 13
Santiago P

rrProfessor

South West, Ohio

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Gentlemen, Anyone ever heard of mast bumping?

It manifest itself as a wobble when the RPM is too low relative to the dampener hardness.

For old farts like me this is head tuning 101 for FAI machines, which run RPMs ranging from low 1300 to over 2000

The solution is to soften the spindle dampening until the wobble goes away.
Start by taking preload washers off. If that does not work then switch to softer dampeners, OR, hack you curent dampeners.

Santiago

Team Minicopter - PeakAircraft.com
bavarianDEMON- Team Kontronik - Scorpion Motors-

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10-07-2014 09:56 AM  3 years agoPost 14
JKP35P

rrNovice

savannah, GA

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The shims that you use to shim the main gear to the pinion on your transmission

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