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Old Nov 18, 2012, 08:07 PM
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Motor gearbox for a tug

I'm going to start a tugboat and was wondering if anyone has used this type of gearbox from Hobby King?
http://www.hobbyking.com/hobbyking/s...dProduct=15245
I know it's only a 4:1 ratio but I'm thinking of a low Kv brushless motor with a marine ESC. I fly RC models but my boating experience has been limited to rc sail so far.
KJH
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Old Nov 19, 2012, 01:55 AM
NeverAgainVolunteerYourse lf
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I've used a similar Maxx 3:1 gearbox in the past, but have found plenty of low Kv out-runners tthat don't need a gearbox, depending on the prop size anything from a 700 Kv to 1000 Kv works well on 2 cell lipo or 6-8.4 volt (nimh ), the gearbox becomes useful if you want to run higher voltages and/or big props.

What size prop do you intend to use? check out my blog for the article I wrote on this subject

Nick
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Old Nov 19, 2012, 09:23 AM
Veni, Vidi, Feci
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Agreed, should be fine, and the gears look quiet enough (brass pinion on nylon gear, relatively fine pitch). As Nick says, the prop diameter will dictate the required output speed, and from there you can look at various kV's and ratios.
See my article for a typical prop speed chart:
http://matthewsmodelmarine.wordpress...all-geared-up/
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Old Nov 19, 2012, 04:12 PM
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The tug I'm working on is a 900mm long and I have a Billings 50mm brass prop. My original intention was to use a brushed motor but I havent been able to find a suitable gearbox. When I saw the Hobby King gearbox which takes a 28mm brushless motor, I thought that it might be a possibility. There are several motors around the 1000Kv available. The thing that has worried me is the usual brushless motors are low mass compared to brushed motors and consequently over heating in a boat might be a problem. Electric powered boats is a new field for me.

Nick
Your other comment about 700Kv or under motors maybe not needing a gearbox is interesting. And how do I find your blog?
KJH
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Old Nov 19, 2012, 04:18 PM
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Patmat
I have read your article and filed it away for future reference. A quick check with Hobby Lobby doesn't show any of those gearboxes being in stock. Or else I haven't figured out how their site works yet. Thanks for your reply.
KJH
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Old Nov 19, 2012, 05:13 PM
NeverAgainVolunteerYourse lf
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Hi,
Just click on my user name, its a PDF file. I've never had a over heating problem the watts are relatively low in comp. to an airplane motor.
Cheers
Nick
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Old Nov 19, 2012, 05:53 PM
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if you want to go direct drive brushless:

http://www.engel-modellbau.eu/catalo...oducts_id=2426
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Old Nov 19, 2012, 06:04 PM
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Sorry, old article... Master airscrew is no longer available, and HL stopped carrying Graupner. See graupner-usa...
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Old Nov 19, 2012, 10:49 PM
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Gearbox

This one is made by KYOSHO, costs about $10.00, uses metric r/c car pinion's, they cost about $5.00. I am running about 3-1, the motor is an Enegy 55turn, lathe motor. It is driving a 2'' Prop Shop prop,in a Robbe nozzle. Has shown NO wear, in the approx. 6+ years, it has been in the boat. CaptCB
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Old Nov 20, 2012, 05:17 AM
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Thanks everyone. I like the idea of a direct drive so I will order something with a low Kv and see how it goes.
KJH
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Old Nov 20, 2012, 10:40 AM
Straight up is all I ask
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Tower hobbies has a gearbox with a few ratios .
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Old Nov 21, 2012, 08:26 AM
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Note that kv isn't everything... With direct drive, you'll need a hefty motor. With gearing, you can get good power with a smaller motor running faster.
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Old Nov 21, 2012, 08:40 PM
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Quote:
Originally Posted by patmat2350 View Post
Note that kv isn't everything... With direct drive, you'll need a hefty motor. With gearing, you can get good power with a smaller motor running faster.
Point taken. I have probably gone overboard but I have ordered a 530Kv 800W motor. You can't get small motors under 700Kv it would seem. If it proves the wrong choice I can always build a "big" plane.

I come from a electrical background and my thinking is the prop will require a certain amount of energy to spin it at a certain speed in water. So, if I'm on the right track, a small high speed motor working through a gearbox and a low speed motor with direct drive should bith draw about the same current.
KJH
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Old Nov 22, 2012, 01:59 AM
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DT 700 is a very good motor for a 50 mm prop on 6-8 volts

http://www.hobbyking.com/hobbyking/s...ner_700kv.html

expect no more than 10 amps draw,

Your right about low Kv small motors, there's not a great deal out there. The 28mm and 36 mm motors are similar physical size to the standard brushed motors and from experience your spot on with this
Quote:
So, if I'm on the right track, a small high speed motor working through a gearbox and a low speed motor with direct drive should both draw about the same current.
providing the prop shaft speed is the same.

Cheers
Nick
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Old Nov 22, 2012, 05:19 AM
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Quote:
Originally Posted by nick_75au View Post
DT 700 is a very good motor for a 50 mm prop on 6-8 volts
http://www.hobbyking.com/hobbyking/s...ner_700kv.html
Cheers
Nick
I have one of those in my box of bits. Bought for an aircraft that has yet to be finished. I was looking for something lower in Kv but now I will have two possible motors to experiment with,
KJH
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