Brushless Motor Selection

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Brushless Motor Selection

Postby Blocka2 » Fri Mar 02, 2012 8:45 am

During the course of my hobby I have always used brushed motors to power my scale tug boats etc.
With the advent of brushless motors I have looked long and hard at these motors and for the life of me I can't work out how these things are rated.
I need high torgue and low revs. From the information given by most suppliers, I understand the kv rating ie speed per volt. However I get the feeling that the brushless motors are primarily designed for speed. Am I right in my assumption?
Also it appears that I would not be able to power the brushless motor via a conventional gel battery, due to the high current drawn by these motors.
So, am I stuck with brushed motors?
Any ideas.
regards
Paul
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Re: Brushless Motor Selection

Postby Blocka2 » Fri Mar 02, 2012 8:47 am

I might also add that the prop size is rather serious at 90mm 4 blade.
regards
Paul
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Re: Brushless Motor Selection

Postby quarry44 » Fri Mar 02, 2012 7:59 pm

90mm?Must be a huge boat.Given that boats tend to be on the water for much longer periods,I agree that brushless doesn't really work that well in boats.You can get low(300kv+-) motors,but even a 5000mah lipoly wouldn't last more than 10 minutes max.I don't think a 7A gel cell would be much use,as you would be drawing upwards of 60 amps with that kind of motor.Gel cells aren't really able to cope with that sort of draw.
I have seen a brushless motor used,but this was a high speed destroyer type of ship,and relatively small 4-500mm lenght at that.
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Re: Brushless Motor Selection

Postby Blocka2 » Fri Mar 02, 2012 8:40 pm

Thanks quarry44. Kinda expected that was the case. Two 90mm prop's in kort nozzles make for huge bollard pull. Tug is the "Yarra" at 25th scale, so its about a metre long.
So you can see the need to spin these at low revs. I am reducing the 950 brushed motors by 5 to 1 via belt drives.
I also have a shovel nose hydro in which the brushless motor might be more suited. I used a brushed motor in this a few years back and even though it was heavy, it was an exciting experience.
When I finish the Yarra I might look at this again.
Thanks
Paul
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Re: Brushless Motor Selection

Postby cynr100 » Sat Jun 09, 2012 1:24 am

withdrawn
Not enough time in the day for all my crazy ideas, I'm not slow, I'm just pacing myself
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