Motor size mystery

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Motor size mystery

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2 July 2013 at 12:38 #2278
lnvisibleman
Participant
@lnvisibleman
explanation required of motor sizing
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2 July 2013 at 12:38 #41943
lnvisibleman
Participant
@lnvisibleman
I have been totally unable to find any information regarding the meaning of electric motor sizing !

|Can anyone explain what the numbers mean and how they relate to power output? Just what is the difference between a 400 motor and a 540 ? And how do I calculate what size is needed for a model?

Edited By lnvisibleman on 02/07/2013 12:39:57
2 July 2013 at 12:52 #41944
Dave Milbourn
Participant
@davemilbourn48782
This should help **LINK**

Dave M
2 July 2013 at 13:24 #41945
lnvisibleman
Participant
@lnvisibleman
Thanks Dave !!

Loads of info that seems to tell me nothing except that the numbers don't mean a thing. What happened to standardization?? Take a handfull of 400 motors from different makers and they will all be different. So how is a chap supposed to know which motor is the right one for his model ? GUESS ?? Wouln't it be more useful to designate by power output and torque ? Just like a car, it is the easiest way to gauge performance and suitability.

Edited By lnvisibleman on 02/07/2013 13:25:38

Edited By lnvisibleman on 02/07/2013 13:28:46
2 July 2013 at 13:56 #41946
ashley needham
Participant
@ashleyneedham69188
IM. The 400 500 600 sizes tell you what the size of the can is that is the motor casing. Other than that, as you have discovered there is nothing much else that is standard.

HOWEVER, we are all experts here and tell us what model it is, and how big and how fast you want to go, and we will all guess differently as to what you require. Honest truth.

UNLESS you have a common sort of boat in which case someone may well have built one and has used such and such a combination that works and you can go with that.

Ashley
2 July 2013 at 17:48 #41949
Gareth Jones
Participant
@garethjones79649
Hi IM,

The motor sizing problem is probably even bigger than you think. Even if you know the power and torque of the motor, and that is relatively easy to find or work out, its pretty well impossible to find any information on how much power and torque it takes to drive a given propeller and how much thrust you will get as a result.

As Ashley says, give the forum an idea of the size and type of your model and someone will probably be able to advise you. I have built up a spreadsheet of all my model's performance, some with several different batteries, motors and propellers. If you would like a copy, send me a PM with your email address and I will email a copy to you. It might not help, but it covers a fair cross section of models and should give you a pointer to what will work.

Gareth
2 July 2013 at 18:24 #41950
Gareth Jones
Participant
@garethjones79649
Hi IM,

I just had another thought. There was an article in the special edition of Model Boats, published in 2011 I think, in which Colin Bishop wrote an article on motor selection. The data in it was based on a survey of forum members models. I dont know if the magazine is still available but the original thread is still on the forum here http://www.modelboats.co.uk/forums/postings.asp?th=45505

There is probably a better way of pasting in the link but I haven't worked it out yet.

Gareth
4 July 2013 at 00:32 #41967
Peter Fitness
Participant
@peterfitness34857
Gareth, to post a link, firstly look at the 2 rows of icons on the top of the "Post a reply" box. Hover the cursor over these and you will notice that the 4th icon from the right in the lower row will show as "Link". Click this and a box will open with an area marked URL. Enter the web site address in this area and click OK. Job done. The link will show in your post as **LINK** (as in Dave Milbourn's post above)

I hope this helps,

Peter.
6 July 2013 at 13:48 #42013
Gareth Jones
Participant
@garethjones79649
Hi Peter,

Thanks very much for that explanation, I will try and remember for next time.

Gareth
7 July 2013 at 04:55 #42039
Peter Fitness
Participant
@peterfitness34857
My pleasure, Gareth.

Peter.
9 July 2013 at 13:06 #42090
John Thornton 1
Participant
@johnthornton1
Althought their range is fairly limited, Electronize are the only people I know of who give model boaters any really meaningful information about their motor products. They produce graphs showing approx. current draw for various propeller sizes and battery voltages, as well as giving other useful information such as stall current. Have a look at the motor section on their site **LINK**

It would make life easier if others would follow their example.
17 July 2013 at 09:40 #42208
lnvisibleman
Participant
@lnvisibleman
Gareth, thanks a bunch for the info you sent me. It has been of much help in my motor selection.

For everyone else, the data contained in Gareth's charts are very interesting and I think it would be fantastic to have a much larger data base of similar info.

Thanks all for your help.
18 July 2013 at 08:02 #42234
ashley needham
Participant
@ashleyneedham69188
IM. Is this vexed question of motors for a particular boat? and if so what combination of motor, battery (voltage) and prop were you contemplating? Are you factoring in cost and weight for your choice?

Unfortunately the bare facts do not always bear out "in the boat" as it were, as many people can testify to.

Ashley
25 July 2013 at 08:35 #42348
lnvisibleman
Participant
@lnvisibleman
AN, There is no firm plan as yet other than the model will be a scratch built ( or hack built in my case ! ) and based on MV Tintagel. As yet I haved not settled on overall size for the model but it is looking like it will be around 34" long with a beam of 11.25". As far as displacement, is concerned, I won't have a clue until it's built unless there is a way I can work it out.

Edited By lnvisibleman on 25/07/2013 08:48:37
25 July 2013 at 11:31 #42352
Dave Milbourn
Participant
@davemilbourn48782
I might start with one of these, as fitted to the Sea Commander (which is about the same size as your enlarged Tintagel) **LINK**
Run it on either 2S LiPo or 6-cell NiMH pack and use maybe a 40mm 2 or 3 blade prop.
My rule is always to start from a known combination and then fettle it until it's absolutely right for you.
Dave M
18 September 2013 at 10:54 #43832
lnvisibleman
Participant
@lnvisibleman
Tintagel is up and running now thanks to all the great advice I have received,

Thanks all

Photo coming very soon, assuming test run is sucessful and it doesn't sink.
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