Vintage model motor choice!

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Vintage model motor choice!

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2 February 2015 at 22:42 #55691
Matthew Kerry
Participant
@matthewkerry97541
Hello everyone, I am a newbe to model boats so am in need of pleanty of help!

I recently bought a model of what I would describe as a 1950s style Italian Launch. She is 34" long 8" wide and approx 7" tall weighing just over 3KG. She is fitted with an old motor and prop with the propeller measuring 40mm in diameter. I want to fit it out with full RC controls but am stuck (confused) on what power motor/battery to choose. I want it to have a decent amount of speed and will also be replacing the propellor for a new 45mm 3 blade version I have seen. My main problem is what KV Motor to choose for this size of boat with only a single 45mm propellor. Is getting any decent speed even possible with this or would it need twin props?

Thanks in advance for any help!

Edited By Matthew Kerry on 02/02/2015 22:56:08
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2 February 2015 at 22:42 #2466
Matthew Kerry
Participant
@matthewkerry97541
And Prop choice etc etc!
3 February 2015 at 09:12 #55697
Mike Dunn
Participant
@mikedunn19317
Hi mattew, i would suggest an mfa 850 motor and try fitting and the biggest prop that you can fit it looks like you have plenty of room also fit a 12 volt 7 amp-hour battery to give good amount of ballast start from there should go like a rocket you might need to experyment with battery size. looks a nice boat..

best of luck

mike.
3 February 2015 at 09:26 #55699
Dave Milbourn
Participant
@davemilbourn48782
Please forgive me interrupting but "go like a rocket" doesn't square with "12 volt 7AH battery". I presume you mean a lead-acid battery; this will add a lot of weight (2.6Kg) and take up a lot of the motor's power just pushing it around. Unless the model is a displacement type which needs a lot of ballast (e.g. tug) then I would always advise using NiMH or LiPo packs. These will also provide a lot more of their power to the motor, because SLA batteries will only deliver a relatively low current – and the 850 is anything but a low-current motor!
For a brushless motor have a look at the larger one of the two sold by The Vintage Model Co. **LINK** They can also supply a matched speed controller, but don't even think about running this on a SLA battery!

Dave M
3 February 2015 at 14:24 #55704
Colin Bishop
Moderator
@colinbishop34627
Looking at the design of the boat and its hull shape it doesn't strike me as a high speed craft in the Fairey Huntsman mould. It looks more of a brisk cabin cruiser type so for realism it needs to be reasonably quick but not necessarily to plane.

Colin
3 February 2015 at 14:55 #55705
Dave Milbourn
Participant
@davemilbourn48782
Colin

You're dead right. That's a semi-displacement hull, in that it will tend to ride a little higher with speed – but there's no "plane" for it get up on.

Dave
3 February 2015 at 17:41 #55709
Matthew Kerry
Participant
@matthewkerry97541
Excellent feedback chaps! I’m not to fussed about realistic speed but nothing stupidly fast, I had a look at the 850 motor but you cant get a 12v lipo battery only 11v & 14v would the brushless motor in the link give the same performance with a lower volt lipo battery? I will do more research later but thought I’d ask on here too. Really appreciate the feedback thanks.
3 February 2015 at 18:43 #55710
Dave Milbourn
Participant
@davemilbourn48782
That's 11.1v or 14.4v, both measured off-load. Stick an 850 motor across an SLA and watch the voltage drop! The only effect of having a fractionally lower voltage is a fractionally lower speed, all other things being equal. From a practical point of view the voltage of a 3S LiPo is the same as a 12v SLA.

The Turnigy motor will give a sparkling performance on 3S; that's what I would use.

Dave M
3 February 2015 at 20:10 #55714
Gareth Jones
Participant
@garethjones79649
Matthew,

If you plan to go down the brushless/LiPo route I would recommend the following combination:-

Hobbyking Turnigy D3548-6 motor (790kV)

3 s LiPo (11.1 Volts)

45 mm 3 bladed or 4 bladed brass propeller

The above combination will take about 25 amps at full throttle so buy a speed controller with a suitable margin – if you go for a cheap and cheerful one aim for at least 50 amps and preferably more.

It should give you a prop speed of about 7000 rpm and a static thrust of about 2.2 kg

Whatever you do don't use a big lead acid battery, it will be way too heavy and won't sustain the voltage you need to deliver the amps.

Gareth
3 February 2015 at 22:49 #55716
Matthew Kerry
Participant
@matthewkerry97541
Thats great guys, thanks for takng the time I'm starting to get an Idea of what I need, I'm definately going with 11.1v 3s LiPo and a brushless motor, I was almost set on the 1250Kv 38mm Turnigy Dave recomended but now Gareth suggests a 790Kv version!! Which would give me more speed, surely the 1250kv?? I know its probably more technical than that though!? Weight of boat & prop size etc… So which to choose?

Also I looked more into the prop and I may be able to just squeeze a 50mm under her but it would be scratching the paint! And now Ive found there are different propellor pitches too but would really like to know whats better for my boat 3 or 4 blades or is the difference negligible?

Cheers chaps I definately joined the right forum here, Ive also bought a Steam Bowman Luton Snipe which I would like to make a removable RC stearing servo for but that can wait till later!
4 February 2015 at 12:00 #55726
Matthew Kerry
Participant
@matthewkerry97541
Ok so I’ve done my research on propellors and from what I can tell a 3 blade gives slightly better top speed & a 4 blade gives slightly better acceleration and handling but its all so slight I doubt I would ever tell the difference so will go with whatever looks nicest! Just still a bit confused on which motor 970kv or 1250kv.
4 February 2015 at 19:20 #55745
ashley needham
Participant
@ashleyneedham69188
Matthew. More to the point would be ..in what condition is your propshaft?? does it have bearings either end or is it a plain tube??

You really need to think about replacing the propshaft to cope with all this power, a 4mm diameter shaft will be ok. Personally i would go for one with nylon bearings as they are waTER LUBRICAted…

You can theorise all you want but you will never know what is the best motor unless you fit a whole bunch of them. A 45mm prop i would say needs the lower Kv motor, but you may actually go faster with a smaller higher revving prop, so use the highr Kv motor.

I know this does not ACTUALLY help but thats how the cookie crumbles.

Ashley
4 February 2015 at 20:37 #55749
Gareth Jones
Participant
@garethjones79649
Matthew,

I agree with Ashley,

I think the 790 kV motor I suggested would be the best match for a 45 mm 3 or 4 bladed brass propeller. The faster one Dave suggested on the Vintage Model Boat Co page would be better matched to the 40 mm 2 bladed plastic prop that they illustrate.

If you want to get an idea of what the combination I suggested will do, there is a link here to when I tested it in a Springer tug. **LINK**

Gareth

Edited By Gareth Jones on 04/02/2015 20:38:12
4 February 2015 at 20:42 #55750
Matthew Kerry
Participant
@matthewkerry97541
The props ok but it is just a plain tube so I want to replace it for one with bearings, because of the layout of the boat it will need to be 13" long and I havnt been able to find one that length yet? So if someone knows where to get one please could you let me know where? Also If you have look at the picture of the prop on my boat it has a support underneath, I would like to maintain this or get a new one to fit the new shaft, so again where from please?!

Thanks again chaps, I'll stop asking questions soon!
4 February 2015 at 21:44 #55752
Matthew Kerry
Participant
@matthewkerry97541
Thanks Gareth, SOLD! I'll go with that combination. Im obviously new to boats and just the other day I would of thought the higher the KV rating the better it would be for my boat so a big learning curve for me! Ive measured up and think im going to go with either a 45 or 50mm Raboesch 3 Blade Skewed power propellor. Could you let me know if I need a LH or a RH?? Also I cannot find a 13-14" sealed bearing propshaft to suit my needs as I want to keep the exposed shaft with P hanger. Do these exsist with sealed bearings?

Thanks, Ill post some pics of my progress somewhere.

Edited By Matthew Kerry on 04/02/2015 21:59:12

Edited By Matthew Kerry on 04/02/2015 22:04:28
4 February 2015 at 22:47 #55753
Matthew Kerry
Participant
@matthewkerry97541
Just one more question! (for now) What Battery? I know you said a 3S LiPo but what mAh & what discharch? Ive seen one which is 11.1v 2200mAh constant discharch 30c peak 40c, will that do?
4 February 2015 at 23:17 #55755
Dave Milbourn
Participant
@davemilbourn48782
Matthew

You don't have to use LiPo batteries for brushless motors. NiMH packs are far more cost-effective where weight is a secondary consideration i.e. you will obtain about 100 charges from a LiPo pack at the very best, whereas if you look after a NiMH pack you'll get over a thousand. Whichever you choose go for the biggest capacity you can afford. This supplier is one of the very best for price, quality and service. **LINK**

BYW I wouldn't disagree with Gareth's choice of motor; mine was based on someone else's experience whereas Gareth has first-hand knowledge of these alien devices. I'm catching up!

Dave M
5 February 2015 at 08:12 #55756
ashley needham
Participant
@ashleyneedham69188
matt. The shaft length you need is the distance from the prop to the end of the coupling on your motor.

As illustrated, your boat has a geared unit with motor underhung. If you are going to use a new motor and coupling you will need to reduce the new prop tube length.

You could also usefully reduce the angle of the propshaft keeping the motor low and the shaft more shallow,

I would suggest buying a bunch of two blade plastic props 35mm-50mm diameter in S and X pitch . These plastic props are very cheap, and you will have a yardstick to judge performance by when you spend 20 times more on a snazzy brass one that does not perform as well……..S and X.. x pitch much courser.

The props hand is such that the motor tightens up on the thread into the prop when driving. i think different manufacturers describe left and right hand pitches differently… the way round a plastic p[rop goes is the correct way.

Nimh`s definitley

Ashley

Edited By ashley needham on 05/02/2015 08:15:37
5 February 2015 at 10:45 #55757
Malcolm Frary
Participant
@malcolmfrary95515
Whatever props you use, use locknuts, and maybe some Loctite. While it can be true that in normal running a RH prop will tighten on the shaft, it is very true than an unlocked one will unscrew itself on applying reverse. The opposite is true of LH props, and, as Ashley mentioned, the continentals take the opposite view of prop handing. There is a modest fortune in brass on the bottom of most sailing waters, so locknuts are good..
5 February 2015 at 12:55 #55758
Matthew Kerry
Participant
@matthewkerry97541
Thanks Ashley, the current shaft is 16″ so I measured back from the propeller to where the new motor would have to sit to clear boats top cover when fitted as the centre wheel house area dips right down into the hull so it would need to be 13″ long.
Cheers

Edited By Matthew Kerry on 05/02/2015 12:56:05
5 February 2015 at 12:59 #55759
Matthew Kerry
Participant
@matthewkerry97541
Just been looking at speed controllers and the marine ones are all water cooled, is this necessary and do I just attach a tube to an intake through the hull (drill a hole) or does it requre some sort of pump?
5 February 2015 at 13:41 #55762
Dave Milbourn
Participant
@davemilbourn48782
Have a shufti at this thread **LINK**

DM
6 February 2015 at 07:44 #55765
Matthew Kerry
Participant
@matthewkerry97541
Ok had a look at those and it all looks pretty simple. What happens if the motor or speed controller does over heat? Does it just shut down for a short while whilst it cools down and then works again or does it cause irreversible damage?
Thanks, Matt
6 February 2015 at 08:51 #55767
Dave Milbourn
Participant
@davemilbourn48782
You would need to look carefully at the specification of the speed controller to find that sort of detail.

DM
8 February 2015 at 23:30 #55820
Matthew Kerry
Participant
@matthewkerry97541
Ordered the HK Turnigy 970kv motor today along with a water cooled 50Amp ESC and 4000mAh 30c battery. Just need a suitable propshaft now which must be a mimimum of 13" long.

Matt.
Author

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