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Author Topic: What motors would you suggest?  (Read 2127 times)

Walnut

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What motors would you suggest?
« on: February 19, 2018, 01:26:16 PM »

I'm about to embark on my first proper build. It's a semi scale 1m predreadnought with a plywood and light ply hull. I want to use a 12v 7ah SLA battery as power and ballast.
What single motor would you suggest or what pair of motors you suggest.
Thanks in advance for the advice.
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Martin [Admin]

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Re: What motors would you suggest?
« Reply #1 on: February 19, 2018, 01:44:56 PM »


How many motors does it need (prop shafts) ?
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chas

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Re: What motors would you suggest?
« Reply #2 on: February 19, 2018, 03:01:21 PM »

MFA 385 motors should be ideal. OK whether you need 1 or 2. They have 5 poles, good torque, inexpensive and reliable. Rated 4.5 to 15 volts. I use them in a similar model, and they've been reliable for years. With a 7 amp battery one motor will run approx 6 hours, depending on the prop.
Chas



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Walnut

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Re: What motors would you suggest?
« Reply #3 on: February 19, 2018, 03:15:49 PM »

I can make it with one or two motors. The line drawings show two motors and one rudder. As I am planning to build the hull 'Glynn Guest style' I could also build it with one motor.
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Walnut

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Re: What motors would you suggest?
« Reply #4 on: February 19, 2018, 03:27:28 PM »

Thanks for the advice Chas.
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unbuiltnautilus

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Re: What motors would you suggest?
« Reply #5 on: February 19, 2018, 06:54:42 PM »

One motor on 12v I would suggest the MFA 540LN variant of their 540 can motor. Very silly short motor shaft ( will still fit a standard three part U/J ), but quiet and high torque up at 12v.
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Walnut

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Re: What motors would you suggest?
« Reply #6 on: February 20, 2018, 11:17:53 AM »

Thank you all for your advice. its time to cut the wood.
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Tug Fanatic

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Re: What motors would you suggest?
« Reply #7 on: February 20, 2018, 12:39:56 PM »



You need to match the hull with the motor & with the props. As you know the size of the hull you need to decide what size props will you be using & how many of them.


I don't know what size prop either a 385 or 540 will cope with on 12v but I am suspicious that it will nor be very large without overloading the motor.


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Walnut

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Re: What motors would you suggest?
« Reply #8 on: February 20, 2018, 12:56:42 PM »

I'm leaning towards 1 motor, 1 esc, 1 prop and 1 rudder for ease of build, because it will all be out of view. At the moment I have not considered the prop size. I was going to determine that by looking at the line drawings of russian pre dreadnoughts and working out the scale size for a prop.
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Tug Fanatic

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Re: What motors would you suggest?
« Reply #9 on: February 20, 2018, 01:22:48 PM »


I'm leaning towards 1 motor, 1 esc, 1 prop and 1 rudder for ease of build, because it will all be out of view. At the moment I have not considered the prop size. I was going to determine that by looking at the line drawings of russian pre dreadnoughts and working out the scale size for a prop.


You will obviously need to build the model to give clearance for the prop that you want to use. If it was me I would want to know what prop size/ number of blades I intended to use before deciding upon the motor & certainly before getting too far into the construction. Can you work out the scale prop size now? I expect that the original had rather more than one prop.
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Walnut

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Re: What motors would you suggest?
« Reply #10 on: February 20, 2018, 01:36:25 PM »

When I get back home this evening I'll post more details  :-))
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chas

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Re: What motors would you suggest?
« Reply #11 on: February 20, 2018, 02:29:06 PM »

It's not difficult to work out. The model is around 1 metre, it's based on an 1900ish prototype so the scale must be between 1/80 and 1/100.  Ideal prop size for this model and type will be 30 mm, 3 or 4 blade brass. 25 mm will do if there isn't enough clearance for 30 mm.
 For comparison, Deans Marines HMS  Amazon, (1900) nearly a metre long uses this size, as I do with 2 of my models. ( 3 blade props)  general advice for this style of ship model is to keep the centre of gravity as low as possible, they can be a bit twitchy otherwise. This is partly why I suggest a 385 motor, it is a smaller diameter than 500 series motors and can be mounted lower. The power will be more than enough in a long narrow model and on 12 volts it will be running well throttled back most of the time.
Chas


 
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Walnut

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Re: What motors would you suggest?
« Reply #12 on: February 20, 2018, 02:55:45 PM »

Thanks Chas. I've just posted some proper details of the proposed build in the Warships R & D section. 'Pietropavlowsk'
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malcolmfrary

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Re: What motors would you suggest?
« Reply #13 on: February 21, 2018, 10:15:52 AM »

For the performance required to look right on a pre-dreadnought battleship, a 545 or a 385 running on 12 volts will be very adequate, just make sure that the prop used is not of bigger diameter than the motor casing if using direct drive.  The 385 will benefit from gearing rather than direct drive with a larger prop. 
Being a battleship, rather than a destroyer, and having a 7AH 12 volt battery sat in it, it won't be in the least twitchy unless the battery is fitted upright. 
I would go for a plastic prop and paint it with bronze metallic paint with a drop of green mixed in.  Or a home made brass one according to the ideas put out on http://towboatjoe.tripod.com/shafts.htm
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Walnut

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Re: What motors would you suggest?
« Reply #14 on: February 21, 2018, 11:54:30 AM »

This is exactly why I joined the the forum. Lots of advice and opinions. Far better than solo research on the web. Ta.
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RST

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Re: What motors would you suggest?
« Reply #15 on: February 21, 2018, 11:16:15 PM »

I would say for someone unexperienced to ask advice and be recommended some guidelines is fine -then to be suggested to make their own prop as an alternative is somewhat contradictory unless it's an ultra cheap build or someone tool-equipped.  Better things to worry about than making your own propellers most of the time.  Some good pointers so far, if it gets you going buy a plastic prop (3 maybe)  first then if it's ok buy a brass one (10+) -no need to make your own unless youre into fine-scale, which it sounds like in no way this isn't.  For what its worth I'd try a 385 first but I would suggest to allow for a bigger motor and a few mm prop clearance (500 can size etc) to be fitted in the same space anyway.  Gives a bit of flexibility.
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roycv

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Re: What motors would you suggest?
« Reply #16 on: February 22, 2018, 12:42:32 AM »

Hi all, I refurbished a Model Boat plans Dreadnought a while back and that had 2 off 5 pole 385's running on 6 volts.  This boat, at about 30 inches loa, would be about half the displacement of your one.  Performance of my one was fine and it went forever on a 6 volt SLA battery and one 10 amp esc.
When buying an esc to run on 12 volts make sure it is suitable.  Most of the cheap esc's top out at 8 cells.
I recently bought a new to me type esc recommended on another thread that was for 12 volts.  It is only meant for lightish work (10 amps) but it does not have a heat sink and weighs just a few grams and works well for me. (I think I found it on Bang good .com)

The only diiference to the usual esc is the power connector, it is not a Tamiya white connector but uses the same connectors as the red 4.8 volt leads that are i/p power to receivers.  I bought some red leads very cheaply and made up a conversion plug / socket.  You could easily cut the leads and connect the smaller red leads.

One point to think about is the prop tubes, the usual brass ones are rather large in diameter, I have been using smaller diameter prop tubes but still with an M4 thread shaft (or 4BA).
The advice on prop versus motor diameter usually works, but I would go for 25 -30 mm pros with a big pitch.  Some of the plastic ones are very fine pitch and will get you nowhere.

Do not use the very small U/J connectors as they easily fracture at the spline part of the unit.

The larger ones are much stronger and you can buy the 2 brass parts to customise to your requirements.  I think the 385 shaft is 2.3 mm diameter and M4 is readily available or if the drive end of the prop shaft is plain then that will be 4mm dia.
Hope this helps, sorry can't remember the exact  ESC type but it was mentioned in a thread about 6 weeks ago and I went on the web site and bought the 12 volt version.  6 or so I think.
regards Roy
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malcolmfrary

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Re: What motors would you suggest?
« Reply #17 on: February 22, 2018, 09:23:45 AM »

I would say for someone unexperienced to ask advice and be recommended some guidelines is fine -then to be suggested to make their own prop as an alternative is somewhat contradictory unless it's an ultra cheap build or someone tool-equipped.  Better things to worry about than making your own propellers most of the time.  Some good pointers so far, if it gets you going buy a plastic prop (3 maybe)  first then if it's ok buy a brass one (10+) -no need to make your own unless youre into fine-scale, which it sounds like in no way this isn't.  For what its worth I'd try a 385 first but I would suggest to allow for a bigger motor and a few mm prop clearance (500 can size etc) to be fitted in the same space anyway.  Gives a bit of flexibility.
Before decrying the notion of a home made prop, I suggest a look at the link.  It follows the ideas that I used some 30 years back, tools consisted of a pair of tin snips, a drill, a file and a soldering iron.  A junior hacksaw, a sharp nail and a piece of wood were in there as well.  Neither rocket science nor jewelry making, all of the tools are what anybody doing model making can reasonably be expected to have.  Making your own does not have to involve either a lathe or silver soldering unless you want something that will stand scrutiny in a museum.  Using the method in the link ( http://towboatjoe.tripod.com/shafts.htm ), as a bonus, you get to have adjustable pitch as well.
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roycv

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Re: What motors would you suggest?
« Reply #18 on: February 22, 2018, 09:35:33 AM »

Hi Malcolm, nice to see tow boat Joes web site still in use I used to have an occasional email exchange with him until he died a few years ago.  I got ceased up on a Mississippi towboat kit from Dumas, what with 6 rudders etc.
I remember making a propeler in that way back in the 70's, works OK, depends on how much time you have.
regards Roy
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malcolmfrary

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Re: What motors would you suggest?
« Reply #19 on: February 22, 2018, 09:07:33 PM »

Hi Malcolm, nice to see tow boat Joes web site still in use I used to have an occasional email exchange with him until he died a few years ago.  I got ceased up on a Mississippi towboat kit from Dumas, what with 6 rudders etc.
I remember making a propeler in that way back in the 70's, works OK, depends on how much time you have.
regards Roy
A further thought on his prop method was to use a M4 brass nut and solder it to the prop rather than to a brass shaft.  That way, a regular model shaft could be used which would also use the outer sleeve and bearings, rather than the concentric tubes.
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roycv

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Re: What motors would you suggest?
« Reply #20 on: February 22, 2018, 09:15:02 PM »

Hi Malcolm I seem to remember doing that but my 70's date is wrong it was previous decade as mine was 4BA before 'the metric' and I was doing an evening class in metalwork in NW London at the time and an early job for me was making a locking nut tapered off and polished up.  Still got it in my prop box, I did have it on a boat but found that a plastic prop was much more efficient.
Happy days!
Roy
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Walnut

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Re: What motors would you suggest?
« Reply #21 on: February 23, 2018, 10:18:59 AM »

Thanks everyone. I'm not ignoring the thread, I was diverted by domestic tasks set by SWMBO.
I'll update the build as soon as I can. Once again thanks for the advice.
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