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Old Mar 05, 2011, 10:55 AM
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will this Gearbox work with this motor

Folks,
Im buying Greatplanes Siren hotliner glider and because the budget it limited , Im planning to buy the power system from HobbyKing.com , and try it out....and the one I chose is Turnigy:
http://www.hobbyking.com/hobbyking/s...idProduct=4200

now I wasnt sure what to do with the Gearbox, apparently I cant get any gearbox that works for the application from Hobbyking. The recommended gearbox is:
http://www3.omnimodels.com/cgi-bin/woi0001p?&I=GPMG0520

and apparently it has been made for Ammo motors, but can anyone tell me if it will work with this Turnigy motor ?
The only thing I looked at and wasnt sure was the motor shaft diameter 3.2mm in compare to the gearbox input diameter 3.175mm

I dont know if that little will be a problem or not.. so I decided to seek some advice from pros.

any help would be highly appreciated.
Ben.
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Old Mar 05, 2011, 11:13 AM
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It should be fine... the gearbox comes with a 3.2mm bore pinion (3.175mm, 3.2mm and 1/8" are all the same in the RC business!) which is what you need for that Turnigy motor. Mounting holes are standard for 28mm inrunners, so the motor should bolt correctly to the gearbox.
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Old Mar 05, 2011, 11:33 AM
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Originally Posted by Dr Kiwi View Post
It should be fine... the gearbox comes with a 3.2mm bore pinion (3.175mm, 3.2mm and 1/8" are all the same in the RC business!) which is what you need for that Turnigy motor. Mounting holes are standard for 28mm inrunners, so the motor should bolt correctly to the gearbox.
If thats the case,, then I will be fine then. Thanks.
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Old Mar 05, 2011, 01:37 PM
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Quote:
Originally Posted by falcbenry View Post
The only thing I looked at and wasnt sure was the motor shaft diameter 3.2mm in compare to the gearbox input diameter 3.175mm
It might be a problem. 0.025mm is a pretty small difference, but if the pinion is designed to be an interference fit then it probably won't fit on the Turnigy.

If the motor shaft diameter is too large then you could try reducing it, by holding a piece of fine sandpaper on it whilst running the motor.
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Old Mar 05, 2011, 01:52 PM
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None of these motor shafts are exactly what they are said to be anyway.. I've measured dozens of 'em and they are usually under-sized... 3.14, 3.16 etc.... I don't recall that I've ever found one to be exactly 3.2mm......and I'll bet the pinion is unlikely to be bored to 3.175mm exactly anyway. There is always some work to do to get 'em to match up... Loctite 638 is your friend if the interference fit is too sloppy.
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Old Mar 05, 2011, 02:48 PM
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Tolerences are NOT specified in RC equipment. It is pot luck if they are right on.

American SAE tolerances for shafts & holes mean nothing.

Get lucky or use the Locktite. Locktite NEEDS at least 2 days in warm weather. 3 would be better.

WARNING !!!! NEVER LET IT dribble on to the teeth or into a motor BEARING. DEATH to either one. Alcohol cleaning of shaft & the hole is REQUIRED. part or finger oils weaken the grip of the Locktite.

I would LIGHTLY coat... JUST... the shaft, the same distance as the gear will slide on. Gear on a flat surface. Pick up the motor. Slowly slide the motor shaft into the hole.
STOP if the Locktite starts building up on the gearhole too much. Remove the shaft & SOAK UP the excess Locktite with a Kleneex or NEW paper towel. NO Locktite on the gearteeth. Start the shaft in again.

Piece of cake.

When dry. MAKE sure the gearteeth are running true.
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Old Mar 05, 2011, 03:36 PM
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excellent information , on sanding down the shaft and also using loctite.. appreciate all. Where do I get Loctite from ? hobby shop or hardware store ?
Cheers
Ben.
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Old Mar 05, 2011, 03:40 PM
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Home Depot or Lowes or hardware store.
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Old Mar 05, 2011, 04:04 PM
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Originally Posted by Dr Kiwi View Post
I don't recall that I've ever found one to be exactly 3.2mm....
Usually when they say '3.2mm', it's actually meant to be 3.175mm (AKA 1/8"). However I do have one motor whose shaft measures exactly 3.2mm.

A Turnigy B2835-3900
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Old Mar 05, 2011, 04:08 PM
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Bruce

When do you sleep ??
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Old Mar 05, 2011, 05:59 PM
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By the way guys,, what does the KV mean by these brushless motors,,?
Lets say they call it 3900kv or 4400kv,,,
what does kv stand for ?
Thanks.
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Old Mar 05, 2011, 06:07 PM
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Kv is the speed of rotation/volt.

With no load @ 10v one could expect a 3900Kv motor to spin at ~39000rpm (in reality it will be slightly less than that since no transfer of energy is perfectly 100%, nor is a motor frictionless).

Under the load of the correct-sized prop one should expect a motor to spin at better than 75% of Kv x V [any less than that and the motor is likely over-loaded].

High Kv motors are suited to speed applications with small props (unless geared for larger props or helicopters).

Low Kv motors are more suited to spinning larger props, to obtain lots of thrust.
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