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Author Topic: motor size  (Read 210 times)


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motor size
« on: April 28, 2021, 02:59:30 pm »

I am currently building a 1/7th model of a 26-foot Victorian Selway fisher steam launch.
I would like to use an electric motor inside a mock steam plant as this is my first attempt at model boat building could someone please advise on a suitable unit and speed controller as I am using a five-blade slow rev propeller.


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Re: motor size
« Reply #1 on: April 28, 2021, 11:26:35 pm »

The Selway WEB site provides an excellent reference for many of their vessels, however you may need to be clearer in which individual hull you intend to choose, as the displacement varies with beam dimensions etc

The steam engine [installed] HP is listed for the majority of varients, and a few propeller sizes are listed  [steam varients with oversquare diameter to pitch], however I would have thought most used 3 blade steam propellers over a 5 blade

The T12 or T24 [12/24 volt motors from disabled scooter type things] are looking as possibilities, as would an automobile dash ventilation fan motor ....[similar to the T series] low speed, high torque, low current consumption ....OK with a 4" diameter propeller & suitable for R/C speed controllers...... so the motor canister diameter could be disguised in or as a ~~100 diameter horizontal steam boiler]

Derek Warner

Honorary Secretary [Retired]
Illawarra Live Steamers Co-op


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Re: motor size
« Reply #2 on: April 29, 2021, 09:28:08 am »

Depending on the value of "slow" and the size and shape of your prop, this might fit the bill - - available elsewhere at lower cost, but this one claims to have them in stock.
An Mtronics Marine viper 15 will work it OK.  Or a 25 for a bit more safety margin.
General rule of thumb for brushed motors - " Motor diameter should be not more than prop diameter, the motor should have more poles than the prop has blades."  A gear box effectively increases both motor diameter and pole count, so with a 2.5:1 gearbox, a 3 pole motor acts as a 7+ pole one, and its effective diameter is similarly increased.
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Re: motor size
« Reply #3 on: April 29, 2021, 07:59:15 pm »

For me, a great way of describing how brushed motors work, many thanks (us steam peeps not good with new fangled electric stuff) hope it helps you to BOMER
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