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Which motor?

New to r/c electronics, need advice

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Joe Beckett02/05/2020 12:57:32
16 forum posts
4 photos

Hi All,

Like a number of posters here, I took up model boating again because of the lockdown. I have previously built a Robbe Atlantis that I recently fully restored. I have now just ordered a Lesro Fairey Huntsman 47" model and I am intending to fit it out as close to the original boat and therefore have entered the minefield world of which motor/s to use? I really would like to go brushless and LiPo and also have twin engines. I've researched kv's,T's, can sizes and Watts, so have an idea of what I want but am I heading in the right direction? I would like the finished boat to be able to get up on the plane quickly and have a decent turn of speed but I don't want to break any records! Any advice welcome. Thanks

Chris Fellows02/05/2020 15:15:46
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695 forum posts
411 photos

Hi and welcome Joe

Brushless and LiPos definitely. Thoughts tend to be that twin motor setups aren't much quicker if anything than single so the motor sizes will be pretty much the same.

Initial thoughts would be something like a pair of Overlander 5045/10 720kV which on 4S LiPo would rev at 10600.

Is this around what you're thinking of?

Chris

Joe Beckett02/05/2020 16:11:05
16 forum posts
4 photos

Hi Chris, Thanks for the reply. That's kind of what I am thinking of, although your suggestion may be a little under-powered? That said, I don't know the weight of the finished model yet, so this all might be a bit premature. The model is quite large and I believe largely made of ply so by the time it is all fitted out, I am guessing it might weigh quite a bit. If anyone who owns one knows the all-up weight, that would be really useful. I am looking at a pair of Turnigy AquaStar 4084-1050KV Water Cooled Brushless Motor, although I have no particular experience of this motor, it does have built in cooling and an inrunner is (IMO) easier to fit? Am I right in thinking generally speaking, an outrunner offers a bit more torque and is 'slower' spinning than an inrunner? As I said, it's a minefield!

ashley needham02/05/2020 17:27:17
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6599 forum posts
150 photos

Joe. GENERALLY speaking, in-runners seem to be in the higher revving bracket, but outrunners vary from 40Kv to 10,000Kv (for ducted fan use).

Accepted wisdom here is that a motor matched to the hull/prop may well get warm, but should not necessarily require water cooling. That said, interior ventilation is recommended to stop heat build up.

Sorry, would not like to hazard a guess as to what you might fit. However, fitting a more common size pays dividends if/when you want to swap them out.

DM is the Fairey god and he will lay down chapter and verse as to what you should fit....

Ashley

Dave Milbourn02/05/2020 18:04:00
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4002 forum posts
282 photos

DM is the Fairey god and he will lay down chapter and verse as to what you should fit....

A LESRO Huntsman 31? Never heard of it.

If it's anything like the one from SLEC then I would fit just one motor anyway - one of these G60 outrunner and run it on a 5S or 6S LiPo pack. Other manufacturers' similar products may well be available.

Twin motors = 2 x the expense and 2 x the potential trouble. You won't know the difference once it's in the water, anyway.

The Fairey God has spoken smile d

DM

ashley needham02/05/2020 18:07:26
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6599 forum posts
150 photos

I bow before the master.

Ashley

Edited By ashley needham on 02/05/2020 18:09:06

Ray Wood 202/05/2020 18:15:51
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1992 forum posts
709 photos

The Master has spoken 😀

Joe Beckett02/05/2020 18:39:42
16 forum posts
4 photos

Thanks All, I am honoured to be amongst such distinguished company!😉. Thanks for all the responses, as they say knowledge is power! I may be putting my head above the parapet here but......DM, is a 500kv motor going to get this on the plane and give a decent turn of speed? I believe it is the SLEC model as you suggest,I bought it from Lesro Models in Poole! Do you happen to know how much the model weighs? Call me.........but I really would like to fit twin engines so would really appreciate advice on that set up? Maybe I should wait until the model arrives and go from there?! Ohh the excitement!!! Sounds like I found the right forum anyway! Thanks again.

Dave Milbourn02/05/2020 19:29:09
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4002 forum posts
282 photos

Joe

I designed the original Huntsman 31 @ 1/8 scale in 1972 for Model Avionics, which became Balsacraft International Ltd t/a Precedent Kits. They subsequently became SLEC who now manufacture a range of model boats, some of which were designed a long time ago by Les Rowell and marketed at that time as Lesro Models. After Les's death these were made by a company called Vintage Model Boat Co, which was then sold to SLEC. Are you with me so far?

The original H31 1/8 had a glowplug motor which churned out around 1.2BHP. With a 5S LiPo the G60 should produce 9250 RPM and approx the same power. If you increase that to a 6S pack then the power will comfortably exceed that of the original HP 61F R/C motor. Use a 7S LiPo and it will be ballistic.

The model might possibly weigh a little more with LiPo batteries as opposed to a tank full of glow-fuel, but the performance should be the same if not better. I don't recall weighing the original model but it had enough poke to tow a rowing boat around Danson Park Lake in Sidcup with the late and much-missed John Rudd standing in the bow with the Tx! On that particular occasion I declined an offer of marriage from a woman passer-by with a pram.....

There's no escaping from nutters at a boating lake.

My advice on fitting twin motors is simple - you're on your own.

Dave M

 

Edited By Dave Milbourn on 02/05/2020 19:31:33

Chris Fellows02/05/2020 19:50:36
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695 forum posts
411 photos

Hi again

As Ashley says, inrunners are generally high revving motors and for boat use more suited to very high performance and race craft. With something of the size, weight and design of many of the Fairey Marine model boats what you need is a fairly torquey motor to get it moving and then with sufficient revs to give it a good top speed.

Outrunners are more torquey so one decision made and you need one with quite a large diameter to give the power required. I generally recommend a motor around 900 to 1100 kV as a good compromise but as motor diameters get bigger the kV tend to get smaller hence why I suggested the 720kV motors. The motor DM suggested is even lower which is why he's suggested running on a 5S or 6S LiPo pack to increase the revs and give the performance required. You pays yer money and makes your choice.

I doubt that my suggestion will be underpowered as brushless motors are very powerful for their size, probably the opposite! And you can always increase the volts!

I have one of the big Huntsman, when the kit was produced by Precedent and I'll see how much it weighs. I know it's bloomin' heavy!

Chris

Edit: Dave posted whilst I was rambling so has given you more info.

 

Edited By Chris Fellows on 02/05/2020 19:52:43

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