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[Bryan Young]

Although not quite a "Newbie" to this Forum, I must confess to a singular lack of nous about electric motors.
When I was building rather large models (sometimes exceeding 100lb), I just bunged in any 1 (or 2) motors that seemed up to the job.
But now that I'm engaged in building a single screw boat that has an AUW of around 20lb I'm more than a bit flummoxed.
Everyone seems to talk in terms of "520" or somesuch. I haven't a clue what all that means.
I've been waiting for ages for someone to ask this question (if only to save my embarrasment).
Please (!)....Just what do all these motor numbers signify?
Must be another "Age Thing"......BY.

[Shipmate60]

Bryan,
If you have a bit of time try looking at this thread.

http://www.modelboatmayhem.co.uk/forum/index.php?topic=11713.0

Bob

[Kim]

Hi Bryan,
in the modelling world we all seem to question motor first... You being a sallty old sea dog might like to go a different direction ... given that it is an actual vessel scalled down....

Personally i'd be asking what dia of Prop. what Pitch then what revs i need to make the prop perform given the models length / weight. What speed do i want ..Pure Scale or something more in reserve...?


Given the super availability of motors these days i'm not sure that the old 5 something or other motor mentalitly is going to do her justice ... Now we have more than five poles available at fairly low cost .......... maybe the answer needs looking at again!
Regards,
Kim

[HRVI]

You guys seem to know allot so i will ask my questions here :)

What motor is best for torque around the 400 size & what pole is best?
If i got a 600 motor is the width any more than a 400?

[Bryan Young]

OK folks. I've read the links and tried to understand what you are all on about!
Basically, if I was doing a true scale size prop then it would be 3" diameter (and 3 bladed). I have 2 of this size fitted to "Recorder" powered by 2 car blower motors. Drives beautifully at scale speeds but is also capable of going like a bat out of hell when a collision or something seems imminent. But all this is too heavy for the "Barge". The real boats were capable of around 15 knots...that's knocking along quite well really for a 50ft long boat. But at model size, the size and weight of the motor/prop combination precludes this. I'm perfectly willing to use a smaller prop, but the priority is to keep the AUW down to around 20lb or so. Therefore "heavy" motors are out of the question. Also, I don't know whether to go for 6v or 12v.
My "Bluebird of Chelsea" is of similar size and weight but is twin screw (on 6v). That model appears to be happy running on one screw. Perhaps that's the way to go.....but I'd hate to waste more cash than I need to. BY.

[HRVI]

OK folks. I've read the links and tried to understand what you are all on about!
Basically, if I was doing a true scale size prop then it would be 3" diameter (and 3 bladed). I have 2 of this size fitted to "Recorder" powered by 2 car blower motors. Drives beautifully at scale speeds but is also capable of going like a bat out of hell when a collision or something seems imminent. But all this is too heavy for the "Barge". The real boats were capable of around 15 knots...that's knocking along quite well really for a 50ft long boat. But at model size, the size and weight of the motor/prop combination precludes this. I'm perfectly willing to use a smaller prop, but the priority is to keep the AUW down to around 20lb or so. Therefore "heavy" motors are out of the question. Also, I don't know whether to go for 6v or 12v.
My "Bluebird of Chelsea" is of similar size and weight but is twin screw (on 6v). That model appears to be happy running on one screw. Perhaps that's the way to go.....but I'd hate to waste more cash than I need to. BY.

Thought of gearing them down for a lower speed & higher strength? or the opposite way around

[nick_75au]

For best power to weight in brushed motors gearing is the only solution. The RPM needs to match the prop, bigger props need lower RPM than smaller props, I posted an article for brush-less motors that has a chart for RPM based on prop size built up from the Raboesgh prop speeds

http://www.rcgroups.com/forums/showatt.php?attachmentid=4261513&d=1315289844

A 700 geared 6:1 will drive the 3 inch prop on 12 volts very well as a baseline, the same motor can drive with an 11:1 gearbox a 4" prop pushing a very large hull (over 100 Lb).

Nick

[malcolmfrary]

The rough rule of thumb is that the can diameter of the motor should be more than the prop diameter for direct drive.  A 545 motor (same can as a 540, but more poles) with a 2 or 3:1 reduction should do the job very adequately if run on its rated voltage.
Motors recovered from auto breakers used to be a good option (using TLAR) but with the industry becoming more self regulatory and safety conscious (and profit minded) the chance of having a rummage for a bargain is diminishing daily.  They do have the benefit of rugged construction, they are designed for 12 volts and usually have lots of poles for torque, all of which make them great for large props.

[Kim]

For best power to weight in brushed motors gearing is the only solution. The RPM needs to match the prop, bigger props need lower RPM than smaller props, I posted an article for brush-less motors that has a chart for RPM based on prop size built up from the Raboesgh prop speeds


Nick

Did you not forget pitch ?

I have stayed quiet on this one to see what woud come out and seems not much has changed...

The reason i question is i have sourced some well engineered  direct drive motors.. for more info come see me at the Blackpool model boat show...

Bryan i know i'm not really helping you in this post ..
If nothing better comes out then i will send you a sample you can see for yourself what i'd recomend.
Regards,
Kim

[Kim]

You guys seem to know allot so i will ask my questions here :)

What motor is best for torque around the 400 size & what pole is best?
If i got a 600 motor is the width any more than a 400?

Maybe like a car engine ?
4 may do, but a v12 is nicer :)
Except you don't waste 'fuel' with more poles in the motor
Regards,
Kim

[nick_75au]

Did you not forget pitch ?

No I didn't, Thanks for asking, Are you the vendor that sells the T12 and T24 motors?

Nick

[RAAArtyGunner]

No I didn't, Thanks for asking, Are you the vendor that sells the T12 and T24 motors?

Nick

Anyone please care to elaborate on T12 & T24 motors, thank you.

[tt1]

Mobile Marines sell the T12 and T24 motors.

[nick_75au]

http://www.mobilemarinemodels.com/acatalog/Motors.html

BF24 not T

Nick

[RAAArtyGunner]

http://www.mobilemarinemodels.com/acatalog/Motors.html

BF24 not T

Nick

Thank you.

Site visited and motors (all) now seen. 

[Subculture]

Did you not forget pitch ?

Kim

Nick did state based on Raboesch props, which tend to be about square (1:1 pitch to diameter ratio). If you want to get really technical you need to discuss blade area too. Bottom line is that any motor prop combo generally involves a bit of experimentation if it's a one off.