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Motor sizes and ratios of reductions

R/C Submarine modelers

Re: Motor sizes and ratios of reductions

Postby Bigdave » Mon Mar 12, 2012 7:33 pm

You bet-cha!! Toot Toot!! :mrgreen: BD.
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Re: Motor sizes and ratios of reductions

Postby Sub culture » Tue Mar 13, 2012 4:31 am

What RPM per volt do they turn?
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Re: Motor sizes and ratios of reductions

Postby Bigdave » Tue Mar 13, 2012 9:33 am

Not sure that info is stated in the specs but I can check one of mine.
Normally the brushed motors do not give that info in the specs I have noticed.
Just the brushless ones. BD.
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Re: Motor sizes and ratios of reductions

Postby Bigdave » Tue Mar 13, 2012 10:41 am

Looks like 1000 RPM per volt.
Just in case some do not know the more winds a motor has the slower it will spin.
But the more torque it will have.
The lower the turns it has the faster it will spin.
But it will have less torque. BD.
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Re: Motor sizes and ratios of reductions

Postby Sub culture » Tue Mar 13, 2012 10:55 am

The Graupner range of brushed motors are well documented, probably one of the reasons for their popularity. I use the rev counter on my Eagletree logger to measure RPM on motors of unknown origin, a very useful gadget to have.
6K is much too high for these propulsors, and the motor will pull a lot of amps. 2:1 gearing/belts and it will be spot-on assuming you're happy running a 6volt electrical system.

Robbe now do some modestly sized outrunners with very low KV outrunners, specifically designed for direct drive on large marine props. They do one wound for 300kv, and another for 500kv, designed for 60mm and 50mm diameter props respectively.

http://www.engel-modellbau.eu/catalog/p ... d62d9daaa6

http://www.engel-modellbau.eu/catalog/p ... d62d9daaa6

Engel are supplying the 500kv motor with their Type VII kit. The 300KV motor would work great in the Borei, but don't go too mad on the props pitch.
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Re: Motor sizes and ratios of reductions

Postby Bigdave » Tue Mar 13, 2012 4:50 pm

True enough.
I just don't like fiddeling with gear or belt reductions if I don't have to.
The 60 turn Venom will spin the PJ with no problem and a little extra for a rainy day.
The stick on the left called a throttle does not have to be pushed to the limit and you should be able to cruse very well with less than 1/2 stick.
But that extra power is there if you feel the need!! The need for speed!! :mrgreen:
We are just giving you different options Wayne.
You can't say any of them are right or wrong but all will work. :wink: BD.
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Re: Motor sizes and ratios of reductions

Postby Greg W » Tue Mar 13, 2012 8:12 pm

Since when have you used a throttle BD? I thought that was just for show.Greg
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Re: Motor sizes and ratios of reductions

Postby Wayne Frey » Tue Mar 13, 2012 8:38 pm

I have made my move. I told Mike to make up a 3.5-1 belt drive to go to my special little 500 12 volt motor. Like some things, get as close as you can, and go for it. My guess is it will easily do scale speeds for extended period of time, and overtake an Ohio in the baffles, if needed...
Yall want a build thread? It will take a while. But you are not in a hurry,are you?
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Last edited by Wayne Frey on Tue Mar 13, 2012 9:08 pm, edited 1 time in total.
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Re: Motor sizes and ratios of reductions

Postby JWLaRue » Tue Mar 13, 2012 8:48 pm

Greg W wrote:Since when have you used a throttle BD? I thought that was just for show.Greg

No, no...you don't understand. BD uses a throttle... it's an on/off switch. :mrgreen:

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Re: Motor sizes and ratios of reductions

Postby Sub culture » Wed Mar 14, 2012 4:01 am

Are you making your own propulsor or buying one in?
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Re: Motor sizes and ratios of reductions

Postby Wayne Frey » Wed Mar 14, 2012 6:25 am

I have it already.
Go to build threads and find the x-tail akula, or 4th gen akula, I forget which. You will see the pumpjet I had for that project. I kept a spare. Putting it against the plans I had made up, it is perfect, size wise. I took a 1/96 Seawolf pumpjet, and modified it to look more like the Alorosa pumpjet. From all I have seen so far, I may be correct on the Borei pumpjet as well. It was a good guess on what I call "tendencys" by the Russsians.
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Re: Motor sizes and ratios of reductions

Postby Sub culture » Wed Mar 14, 2012 7:31 am

So you're using one of Dave Merriman's Seawolf propulsors, okay cool. Looks like a pre-swirl pumpjet on the plan, but that could be guesswork. That combination should work well then, Dave tends to go for a more modest pitch on the blades than Prop Shop. If it had been the latter, I would have said 4 or 5:1 gearing as these props are very high in pitch and need a lot of power to push them past 2000 RPM.
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Re: Motor sizes and ratios of reductions

Postby Wayne Frey » Wed Mar 14, 2012 9:15 am

It is not David's. It is Pete P's. Who was kind enough to indulge me with this. I could not have done it without him, for sure.
Look at the Alorsa pump jet pics, then look at the wrap around the Borei. The "tail" of both of them has the hole in the middle of a rounded tip to collapse bubbles.Just another approach to the same ends.. Stealth.
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Re: Motor sizes and ratios of reductions

Postby Sub culture » Wed Mar 14, 2012 11:36 am

Oh right. I'm not familiar with Pete's Seawolf propulsor, so you'll have to figure out the pitch yourself (see below).

Here's some good information on how to work out the pitch of an unknown prop, and get an idea on the speed your boat will do with a prop at a given RPM-

Image

Image

Using the nomogram, you can quickly see that if we have a prop with a pitch of say 2.5", a speed of 3500RPM and 25% slip will give you a speed of about 7mph. Now you know why you don't want high RPM.

Even if our prop turned out to be very inefficient with say 50% slip, you will be looking at about 4.5-5mph.
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Re: Motor sizes and ratios of reductions

Postby Wayne Frey » Sat Apr 28, 2012 6:07 am

Thought I would throw this in for those looking for guidance.400 motors are plentiful. But if you decided to go to 500 size, Look here:

http://www.cornwallmodelboats.co.uk/aca ... tml#aG1788

There are several 500 size motors, but here is the deal. Look close at the specs of the 500E 12 volt.
Low amp, slower turning. That looks like the 500 motor (if that is the size you need). Compare it to the other 500s. It looks like the 500 one would need.

Now, here is a catch. I can not find anyone else who carrys that motor. There might be another source out there, but it is not easy to find.
They are cheap. I already have one for the X tail Akula, and one for the Borei. Before I posted this, I ordered enough motors I will not have to worry about locating any more for any future projects (like a typhoon, Mike class, etc), or replacement. Now you can wipe out their inventory if you want to :)

A slow 500 brush motor with a low amp draw. Perfect.

Just an "old school" kinda guy :wink:
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