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Author Topic: Motor/gearbox for big subs  (Read 7156 times)

Shipmate60

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Re: Motor/gearbox for big subs
« Reply #25 on: August 05, 2010, 06:52:54 PM »

Windsorsub,
I have used 550's on a 3:1 Gearbox for years without any problems.
But I usually run them on 6 volts as this gives about 3000 rpm on the output shaft on the gearbox.
On 12 volts if it is a genuine mabucci you will be getting nearer 6000 rpm plus, this is way to fast for this size of prop.
On 6 volts the motor will pull between 1 and 7 amps from air to load.
This is well within the ESC capacity.
I suspect either the motor is suspect or you are just asking too much driving that prop on 12 volts.
You will have to check the current draw on this motor under load to confirm this.
With your symptoms it does point to the motor.
Is the sub too fast and could 1/2 speed be acceptable, if so go to a 6:1 gearbox or try reducing the voltage to 6 AFTER checking the current draw.
The motors which can cause problems are Jonson motors sold as 550's but on 12 volts will pull excessive current.

Bob

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sheerline

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Re: Motor/gearbox for big subs
« Reply #26 on: August 05, 2010, 10:48:54 PM »

Windsorsub, in answer to your question about connecting an ammeter:
It doesn't matter which line (pos or neg) that you put the meter in, if it reads inthe negative sense just swap the meter leads around.
Simply disconnect one of the battery leads, connect one meter lead to the battery and the other to the terminal feeding the sub. If you have a decent meter you may want to set it on a high current range.... say 20Amp. Fire the boat up in the test tank and give it a good thrash at full throttle, you will get an instant reading of the current consumption of your boat. Do it with the prop fully submerged of course. By the way, if you don't want to risk another speed controller, simply wire the motor to the power input terminals on your wtc and run it without the controller in the circuit, at least you will be able to monitor the motor for ages that way and at no risk to any other components in the system.

Sorry if I'm stating the obvious here, I don't mean to teach grandma to suck eggs as they say.

This is a really weird problem but as you only have a speed controller and motor working together and succesive controllers keep blowing, it can really only be the motor causing them to blow. If your results are inconclusive it may be necessary to simply use a different type of motor. I guess the chaps on here have a wealth of experience with many types and may be better placed to advise than I.
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nick_75au

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Re: Motor/gearbox for big subs
« Reply #27 on: August 06, 2010, 07:34:50 AM »


Question for nick_75au: Where can I get access to the Raboesch data you refer to..




I think they used to have it on their site, Ill be damned if I can find it there.

Nick
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Subculture

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Re: Motor/gearbox for big subs
« Reply #28 on: August 06, 2010, 07:39:17 AM »

Hello all.

As most folks on this side of the pond know, I'm a firm believer in small motors w/gear (or tooth belt) reductions.
Skip Asay

The main thing with any electric motor is to run them within 75% of their rated RPM. If you run the motor much below that, then your turning quite a bit of power into heating the windings, which is a waste and not good for the long term health of the motor, if you run it higher then you're probably not getting your moneys worth.

I personally like direct drive where it is feasible- geartrains add an extra layer of complexity, cost and it's yet another thing to wear out. I find belt drives especially costly, although they are silent, but a 9:1 belt drive is not an off-the-shelf item is it? Gearboxes, unless helical cut (very rare) tend to be noisy and less efficient- planetary designs are the best IMO, being compact, fairly efficient and readily available.

Six of one, half dozen of the other.

Skip Asay

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Re: Motor/gearbox for big subs
« Reply #29 on: August 06, 2010, 10:26:26 PM »

"The main thing with any electric motor is to run them within 75% of their rated RPM. If you run the motor much below that, then your turning quite a bit of power into heating the windings, which is a waste and not good for the long term health of the motor, if you run it higher then you're probably not getting your moneys worth."

True enough. Although it may be clearer if you had said "around 75%".

"I personally like direct drive where it is feasible- geartrains add an extra layer of complexity, cost and it's yet another thing to wear out."

Also true but it's really just a matter of personal preference. Besides, a large motor adds a lot of weight relatively high in the pressure hull which, on a smallish boat, can cause some trimming problems. That said, I'll repeat. It's all a matter of personal preference.

"I find belt drives especially costly, although they are silent, but a 9:1 belt drive is not an off-the-shelf item is it?"

No. it's not. But then, I enjoy making all kinds of weird, off the wall kind of stuff. On top of which....I had a bunch of pulleys and belts at the time and no gears. You gotta "run what ya brung" sometimes.

Skip Asay

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Windsorsub

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Re: Motor/gearbox for big subs RESOLVED
« Reply #30 on: August 14, 2010, 05:50:05 PM »

Good morning,

       I would like to thank everyone who helped out in getting my overheating issue resolved. I would like to especially thank Dave and John for their excellent support in not only getting my subs back in the water, but following up through the various tests I was asked to perform and recommending the solution.

In summary, I changed out the 550 Motor for a 555 model (supplied by Dave) which turned out to be plug and play (thanks John!), disabled the BEC on the ESC and installed a set of NICADS, and finally added a 12V fan from the local surplus store to further reduce the heat inside the WTC.

I ran HMCS Windsor at the lake yesterday for just over 2 hours. The new motor has made an incredible difference not only on how the sub manoeuvres, but at just how slow I can run the sub and control it submerged.

I have now asked Dave to send me replacement motors so I can refit the rest of the fleet.

Many Many Thanks for Canada!

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