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Neptune mod, or late to the party.

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Re: Neptune mod, or late to the party.

Postby Sub culture » Sun Mar 23, 2014 4:55 pm

10 A draw on the motor?!!

What sort of set-up is that?
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Re: Neptune mod, or late to the party.

Postby Bigdave » Sun Mar 23, 2014 5:29 pm

Just theorizing. I don't think 10A is far off with a larger prop.
I don't think it's high either.
This is full power not cruising.
I will have to put the motor and my Rabosche prop in my prop Dyno and get some readings. BD.
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Re: Neptune mod, or late to the party.

Postby Sub culture » Sun Mar 23, 2014 11:38 pm

I would expect a boat like this to pull no more than two or three amps under full load e.g 24-36 watts.

10A is the sort of draw I'd expect from either a very large boat, or an underwater rocket.
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Re: Neptune mod, or late to the party.

Postby Bigdave » Mon Mar 24, 2014 1:20 pm

I just ran the stock TT 550 motor in my Dyno.
I used 5 props for comparison and the voltage was 11.5 from my 3 cell Lipo.
I will list the props from least to most output. That is higher thrust given a higher current load.
The lowest was actually the scimitar after market TT prop.
It was 2.4 amps.
The next was the stock TT prop.
It was 3.0 amps.
I tried a three blade 45mm next.
It was 3.6 amps.
I tried a three blade 55mm next.
It was 4.3 amps.
The highest was the fan prop I am using on mine.(un shrouded)
It was 4.5 amps.
I did not have one of the 45mm four blade Rabosche props the guys in my group are using to test.
It is a fairly low powered motor but has good torque.
Here are the different props.


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Re: Neptune mod, or late to the party.

Postby Sub culture » Mon Mar 24, 2014 2:44 pm

That sounds more reasonable. By your figures it sounds like the larger props are loading the motor too much, and you're probably putting more power into heat than thrust, so a bit of gear reduction would help or you would need a lower revving/torquier motor.
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Re: Neptune mod, or late to the party.

Postby Bigdave » Tue Mar 25, 2014 12:50 pm

My guess the prop Tom is running is most likely in the 4A max range.
Gearing it any will loose any speed he is gaining in using the prop in the first place.
4 amps is well within the motor capability as the motor mount is water cooled.
And the ESC is well above that power.
That does not say it did not fail just that is should not have.
It will be interesting to see what the culprate is. BD.
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Re: Neptune mod, or late to the party.

Postby Sub culture » Tue Mar 25, 2014 1:23 pm

I think that depends on how loaded down the motor is. If you go too far, and bog down the motor then it produces little extra thrust, and just ends up burning the power off in the armature.

I find that sealed lead acid batteries give their best when loaded up to no more than about 1C. The standard pack in the Neptune is 2A I believe, so if the boat is pulling more than that, then that will hammer the battery.
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Re: Neptune mod, or late to the party.

Postby salmon » Wed Mar 26, 2014 11:24 am

I think this weekend I will be able to devote some time to seeing what is going on. Thank you all for your help.
The seven blade offered the least resistance to the motor or drew the least amperage, is it more efficient and still offers the thrust of the ones that draw more AMPS?
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Re: Neptune mod, or late to the party.

Postby Sub culture » Wed Mar 26, 2014 11:54 am

You can go so far with calculation (which can save a lot of pointless empirical testing), but eventually you have to test it in order to find out how well it works in practice. This applies for most things, but especially propellers where there is always a significant fudge factor.

If you have read the book I put up on the Dive-in facebook page, you'll know that the fewer blades a prop has the more efficient it is, in theory. A single prop blade isn't very practical, or well balanced, so for best efficiency a two blade prop is best.

In practice fewer blades tend to compromise the thrust available at low RPM, but usually the best compromise between efficiency and available thrust is a good three bladed propeller.

I recently fabricated some props for the yellow submarine, and used the highly technical process of TLAR (That Looks About Right) when deciding on their angle of attack.

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Re: Neptune mod, or late to the party.

Postby Bigdave » Wed Mar 26, 2014 1:30 pm

The props look good Andy.

Tom, usually less current equates to less thrust output.
I know there are a lot of variables in that statement so don't consider it gospel.
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Re: Neptune mod, or late to the party.

Postby salmon » Sun May 04, 2014 1:09 am

O.K. I did not get to it as quickly as I thought.
So today I got to it and here is what happened.
I took the motor and it ran great when connected directly to battery.
Re-attached the motor and tested ESC would you believe it, it ran fine.
So what was the issue?
Grub screw on the propellor was stripped. So the prop may or may not rotate depending if the grub screw moved in or out.
Once I had the grub screw pushed tight against the shaft, it was super glued on. Hopefully it will remain until the replacement comes.
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Yeah!
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Re: Neptune mod, or late to the party.

Postby salmon » Sun May 04, 2014 11:24 pm

Sam won out on which prop. He really wanted the 6 blade one. So, until he has a need for speed, we will go with it.
Now it is itching to get modified. When I was a kid it seemed all the cool underwater stuff was orange, if I ask Sam, he would probably want it Army camouflage or some military orientation like that ( it is what he is into). Star Trek theme taken by Jeff.....hmmm Star Wars (oh, and May the Fourth be with you) not sure about that. More thinking on that.
If you can cut, drill, saw, hit things and swear a lot, you're well on the way to building a working model sub.
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Re: Neptune mod, or late to the party.

Postby Bigdave » Mon May 05, 2014 12:16 am

Glad you found the problem.
A slipping drivetrain will do it every time. :mrgreen:

BTW last Subrun Larry replaced his Rabosche prop with the fan prop from a pumpjet I was running to see how it worked with a stock motor.
He said the difference in thrust was amazing.
And he never popped the stock fuse.
O!
I love the planes, they look like frogman flippers. :D
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Re: Neptune mod, or late to the party.

Postby salmon » Mon May 05, 2014 3:43 am

Maybe I need several props to change out if the circumstance warrants it.......:-)
Thank you for the complement, but all credit goes to Bob. He did the design work on those planes.
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Re: Neptune mod, or late to the party.

Postby Bigdave » Mon May 05, 2014 12:22 pm

Actually though if you have enough speed so water is actually flowing over the planes the stock versions work fine.
They are useless with the stock prop.
I have a Disney Nautilus and have the planes functioning but only for show.
The boat is quite fast but the size and placement make them about as useless as ti---s on a bull as the old saying goes. :roll:
Like the Neptune I was using the ballast system in the Nautilus to control the depth totally.
David Welch
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