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Author Topic: Brushless motors help  (Read 16208 times)

David_S

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Re: Brushless motors help
« Reply #25 on: October 10, 2008, 05:44:04 AM »

To the best of my (also limited) knowledge, there is no reason for brushless motors to be more current-hungry than brushed motors, in fact the opposite, it is simply that the motors currently available are sold on the basis of their high power output, for the boat/car racer types and model fliers. I have two small brushless motors in a couple of planes, each appears externally identical, but on the same battery pack, one is a low-revving, torquey motor and the other is higher revving. Each is suited for its particular purpose. Perhaps there is simply not a strong enough demand for low-revving, efficient brushless motors for scale boats to make them a financially viable option for the manufacturers?

Having played a little with larger brushless motors a few years ago (in model planes that would take a glow engine of .40-.60), I can assure you that low kv brushless motors do exist, but that good ones are not cheap.
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Garabaldy

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Re: Brushless motors help
« Reply #26 on: October 10, 2008, 08:27:59 AM »

There are hundreds of low kv motoros out there but like david_s says they are not cheap.  going by memory the lowest kv i have seen is 380kv i think.  Steamboatbob did you read what nick_au said regarding his current draw in his springer?  I am hoping to get at least 40 minutes out of my set up using a 12v 7amp battery but time will tell.  Perhaps its a little early to be making bold statesments about brushless motors being useless in scale boats.  Or maybe i am just saying that as i have sunk a chunk of money into doing it!  My understanding of the high current draw which is stated in the brushless motor specs is not what the motor will draw all the time but more the max it will draw when loaded with the maximum size of prop(aero).  I am speculating more than i should so i'l stop.

If i get 40mins run time out of my set up i'l be happy :-)
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steamboatbob

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Re: Brushless motors help
« Reply #27 on: October 10, 2008, 09:31:19 AM »

the setup he is running sounds good 12v with a 1000kv motor will give you a 12000 rpm at the prop and running on a gell cell would give you a very good run time when measuring the current draw on my boats i use my biggest esc i have an old 50 amp from proboat that never goes wrong, i wack the multimeter on it and purchase a esc on the values i get but with brushless is the easy part go to the manufacturers home page and 90 percent of them will tell you what the current draw will be with no load then just try and factor in enough room for the power lower kv moters are good dont get me wrong on this but i just prefer to not to run them in a scale boat as our scale beasties do not need to be seen going quicker than the guys doing their lapsround the circuit lol

this is an article i found to be a very good read By Jay Turner

http://findarticles.com/p/articles/mi_qa3918/is_/ai_n14825517?tag=artBody;col1

these are some data sheets from feigao about their motors and you can see the various amp draw for each type of motor which should help you decide
just remember that the Kv rating is the revs per miniute per voltand you should be fine






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nick_75au

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Re: Brushless motors help
« Reply #28 on: October 10, 2008, 10:06:41 AM »

I run the Springer on 6 volts, still enough power to pull our 11 foot rescue dingy with man on board and 3.5 amps draw, motor specs say it draws 17 amps. Like I said the motor will only pull as much as asked of it.
Nick
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