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[bosun]

Hy guys,
could any of you tell me if this motor that I have would be ok for a tug, the motor is rated 12,volt, it is from a stair lift system so although it is not big it is quite beefy, size being 2,1/2 inches long by 2,inches wide with a shaft of 1/4 inch, dont ask me about metric.
If I run it through a 6 volt battery it runs at what seems to be the right speed for what I want !! and it would have a terriffic amount of torque ( I would think) what size speed controller would I need. The tug is 44 inches long by 13 inches on the beam, and would be using conventional prop (size ? ) and rudderr system ie old steam tug type.
Many thanks in advance.
Bosun

[Doc]

Bosun,
The ESC needs to be able to handle whatever the maximum current draw of the motor is (and just a little bit more as a "fudge factor").
Having said that, there are usually two ways of finding out what the max current draw of the motor will be.  Read the specs of the motor from the manufacturor, or test the motor (stall test).  The specs need some knowledge of motors to be interpreted correctly.  Not always understanding exactly what I read there, my solution is to assume the absolute worst case and use the biggest current draw number as what I'm looking for.  Sometimes means a huge 'over kill' for an ESC but certainly safe ($$$!).  Doing a stall test using the voltage you plan to use will give you a 'base' number to play with.  Add a little to that 'number' for insurance and an ESC that can handle that 'number' should work just fine.
Sound like more work than you thought it would be?  Well, it will be, but not all that bad.  The 'other' way is to ask someone who'z used the same motor and voltage source (let them do the work!).  Being naturally lazy, I like the 'other' idea a lot.  From the ESC point of view, more is better, isn't a bad idea, except for the bank account...
 - 'Doc

If you do the stall test, and if the motor is as powerful as you think, have a few bandades handy if you plan to hold the motor by hand when you do the test.    @#$ things love to chew on fingers!

[Shipmate60]

The motor dimentions do seem a bit small to turn a large prop, but will depend on number of poles and windings. What rpm does it run at, and what size prop will it swing?

Bob

[andywright]

Thats a fair size model, you must be using a 3 inch 75mm prop or larger, you may have to gear that motor. Its hard to say whet its like from a description like that, any chance of a photo with something, ie ciggy packet in photo for comparison, but it does depend on windings.