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Author Topic: Smit Nederland 528  (Read 3849 times)

Terry

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Smit Nederland 528
« on: January 24, 2011, 09:36:40 AM »

I'm about to start building my first boat, the 1:33 Billings Smit Nederland.  I've built RC 'planes and would like to use brushless motors, which I've found to be very efficient, with plenty of suitable control gear available.  I've looked on the forum and found quite a lot about them.  However, what I would like to know is the maximum propeller speed and torque, so that I can size the motors and gearboxes (if 'boxes are necessary).  Also the torque required for the rudder servo.  Billings are pretty useless at giving information - they couldn't give the motor details (they want you to buy their electrical pack ...), the servo torque was given as just kilograms - no cm or metres in the figure, although I could work out what they meant.  But I don't trust them, so would be grateful if someone who has built this model could fill in some details.

Thanks

Terry
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oldiron

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Re: Smit Nederland 528
« Reply #1 on: January 24, 2011, 10:51:45 AM »

  Welcome aboard.
  You may have already checked out this thread on a Neddy build, however, here's the thread in case: http://www.modelboatmayhem.co.uk/forum/index.php?topic=10387.0
  I used 540 motors direct drive. They have plenty of torque to get the job done. As far as the servo is concerned, I can't tell what the torque is. They're a standard size servo that comes with the radio kits that include servos. Funny, something I never worried about when building tugs. Its the kind of thing you get into when building sailing vessel because of the large sail area.
  I don't know how a brushless motor will go in a tug. Most people have shied away from them in this application because the tend to be more of a high speed motor and usually too fast for tug work.

John
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Terry

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Re: Smit Nederland 528
« Reply #2 on: January 24, 2011, 12:26:43 PM »

Thanks oldiron - the thread is v good - you ought to write a book!  As they say, a picture's worth a thousand words, so yours will save me loads of head-scratching.  On the subject ot motors, I guess I've become used to looking for high power:mass ratios for model 'planes, and the brushless are very good in this respect.  Their other benefits seem to be good torque at low speeds and no "cogging" (at least, those with a large number of poles and neoydminium magnets), and the outrunners run fairly cool.  And there are some with low kv values that might do the job in boats.  However, now that you've menioned the 540 motors I can check out the technicals and see if there's a brushless equivalent.  I'm not decrying the tried and tested, and maybe I shouldn't experiment with my first boat.  But that's me ...  From the various pictures in the forum I can work out the servo required.
I'll be back.

Regards

Terry
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oldiron

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Re: Smit Nederland 528
« Reply #3 on: January 24, 2011, 12:46:50 PM »

 Terry:

 I'm not putting down brushless, its just that I don't think a lot of study has been done on them relative to tugs. You may find the odd piece of information on them relative to tugs. I know the question has been raised before. You'll have to let us know what you come up with.

John
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Terry

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Re: Smit Nederland 528
« Reply #4 on: January 24, 2011, 09:25:14 PM »

Hello John
I've spoken to a few model shops and they do sell brushless motors for boats, and some appear to have the right characteristics.  But they're rather vague about the need for gearboxes etc.  I find it extraordinary that nobody can tell me what power and rpm are optimum for various popular model boats, and it looks as though there's a suck-it-and-see approach.  In the model 'plane world, people buy watt-meters, tachometers etc., and make rigs to measure the static thrust, although again, there is some trial and error with selecting the right prop.  I suppose it's more critical with 'planes where getting low mass is important.  The 540 size motor you use is typically about 190 watts, and has a no-load speed of between 15600 and 22500rpm, which will be much lower when fully loaded of course.  3000rpm?  I shall continue investigating and report when I've come up with some sensible answers.  Eventually I'll start building the boat!

Pedantically yours

Terry
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ZZ56

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Re: Smit Nederland 528
« Reply #5 on: January 25, 2011, 12:25:00 AM »

Raboesch does (used to?) list the max RPM for each of their propellers by diameter and type.  Oldiron can confirm this but i believe that the Nederland uses 45mm props which have a max effective RPM of about 7800. 
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oldiron

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Re: Smit Nederland 528
« Reply #6 on: January 25, 2011, 01:27:14 AM »

Terry:

  ZZ56 is correct on the prop diameter ( I just checked it).
  I worked in a local hobby shop for a while and I concur with you on the plane science. The scale boat people never got into it that much. Don't know why. I suspect its because its a far more critical thing with planes to have the correct blade pitch and speed for optimum flying. The same could be argued for boats too. I suspect the go fast boats will be using the same degree of science you refer too, but the rest of us are in the dark ages.
 Also with the brush less motors, they tend to be ideally suited to aircraft (i.e. high speed, light weight and light weight LipPo batteries with higher output than gel cell batteries). In boats, and certainly tugs, we usually need all the weight we can get, hence the biggest gel cell we can pack into a hull with the highest amp hour rating. LiPo's wouldn't help us in that regard. We'd only have to add more dead weight. Too, in Canada, we don't do much in the way of tug competition where a higher efficiency prop/motor combination would be sought. The Barrie Model Yacht Club ran tug towing competitions for several years. I don't know if they're doing it this year or not. Burnaby , B.C. club does too. I don't know of many others, hence most built tugs merely cruise the lakes and ponds without doing any meaningful work. Not trying to be miserable, just an observation and an attempt to explain why model boating is so different from planes.
  That said, I'm interested in hearing/seeing what you come up with. It may change my whole thinking on tug powering.
  On of my other tugs is built with the motor from a car power seat. It direct drives a 3 3/4" 4 blade prop. The combination, running free in the water, can develop enough speed to exceed the hull's ability to keep the vessel afloat. On the other hand, with a load on there is enough torque in the motor to get down and haul. It will easily pull a 14' boat with a 300lb (not me) person in it. So something must be working in that set up.

John
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Terry

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Re: Smit Nederland 528
« Reply #7 on: January 25, 2011, 09:23:07 PM »

Hello John
ZZ56's info is great - it gives me a starting point, and I'm pretty sure what to go for now.  I have several speed controllers and some brushless outrunners, so I'll carry out some experiments and keep you posted as to the results.  By the way, I've built a few 'planes, but spent more time repairing them than flying!  Never got past vertical landing (aka crashing).  So it was a no-brainer to switch to boats, particularly since I have a moat about 1000feet long by average 40 feet wide, and fairly deep.  I can build models to a reasonable standard, and have a well-equiped workshop, and hopefully, by the end of the year, I'll be afloat.
Greatly appreciate the information you and other forum membrs have given.

Regards

Terry
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oldiron

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Re: Smit Nederland 528
« Reply #8 on: January 25, 2011, 09:38:39 PM »

Terry:

 Good luck in the build. That vertical landing thing is the reason I never got into planes.

John
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