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SAB Goblin 630/700/770 SAB Heli Division 630/700/770 - Goblin Helicopters Factory Support


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Old 06-05-2021, 12:52 PM   #1 (permalink)
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Default Kraken 700: helical vs. straight cut gears?

Kraken 700: newer kit with helical gears vs older kit with straight cut gears? What are the pros and cons?
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Old 06-05-2021, 09:08 PM   #2 (permalink)
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Pros: Quieter, less vibration, more modern
Cons: Not sure TBH you'll have to pay for them unless you have one of the newer kits.

I have an older kit. TBH I have gone back and forth about buying them. It's mainly because it's the way I feel it should be. I don't have vibration issues so other than the noise I don't really see an issue.
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Old 06-07-2021, 02:32 PM   #3 (permalink)
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I had what I thought was a bad clicking noise in the gearbox on my yellow kraken build, and a lot of vibration when spooled up on the bench with no head. SAB said no problem it will burn in which I didn't agree with, there seemed to be a lot of backlash in the tail drive which can not improve with time. I've since installed the new gears and its a lot quieter and minimal vibration doing same spool up. Possibly I've over greased it compared to the amount that was in it but I would rather clean a bit of grease off than run gears dry. Thinking about making a vent for the box though so it can't over pressure as it heats up.
The new tail drive is a finer pitch (old gear was about 15T, new about 21T), the input drive is same pitch but both helical cut.
Still finishing build so not flown yet.
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Old 06-08-2021, 12:37 PM   #4 (permalink)
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Quote:
Originally Posted by Stevecg View Post
I had what I thought was a bad clicking noise in the gearbox on my yellow kraken build, and a lot of vibration when spooled up on the bench with no head. SAB said no problem it will burn in which I didn't agree with, there seemed to be a lot of backlash in the tail drive which can not improve with time. I've since installed the new gears and its a lot quieter and minimal vibration doing same spool up. Possibly I've over greased it compared to the amount that was in it but I would rather clean a bit of grease off than run gears dry. Thinking about making a vent for the box though so it can't over pressure as it heats up.
The new tail drive is a finer pitch (old gear was about 15T, new about 21T), the input drive is same pitch but both helical cut.
Still finishing build so not flown yet.
Steve - thanks for posting this.
If one has a kit with the new helical cut gears, does the choice for FBL mount matter? There were several different options for FBL mounting in the manual, but not sure if it matters if the kit has the helical gears?

Lastly, do you happen to have pics of how much lube the transmission has from the factory? That has always been a mystery to those who haven't had to open their transmission.
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Old 06-08-2021, 02:07 PM   #5 (permalink)
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Pic attached. I put more grease in than was there though as mine didn't sound happy and couldn't determine if it was not a lack of lube, but it didn't look like a lot.
Theoretically more lube would be fine if the case didn't pressurise. SAB probably should state how many grams are supposed to be in it.
Most gearboxes have vents for exactly that reason, hence I'm thinking about doing something via the screw on the side that almost looks like it was for a grease port or maybe making a new access cover with a fitting, and run a piece of fuel tubing to a filter. Access cover is probably the better point as shouldn't be much grease in that area.

I'm using option 3 mount due to various posts on HF based on straight gears. The vibes are definitely lower with the helical gears so not expecting a problem. Winter over here, not much flying so don't know when I can confirm how it flys.
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Last edited by Stevecg; 06-09-2021 at 02:26 AM.. Reason: Added pic
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