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Choosing a Motor/Questions

Old 09-21-2008, 05:15 PM
  #1  
FlatSpin
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Default Choosing a Motor/Questions

OK long story short short. i had a 180 brushless out-runner from my old hydrofoam. well i made a scratch build foamie. well that disappeared the other day over the express way. 8 hours of searching and no where to be seen. so 250 dollars of electronic disappeared on a 5 dollar plane. lol. but sad.


any how. so i really have no clue on the real specs of that specific motor.

so to replace it with some else is stumping me kinda.

what im looking for is a motor that is relatively cheap and can handle up to 2 pounds. and is an out-runner.

im looking at the rimfire out-runners from tower hobbies.

my main question is that
http://www3.towerhobbies.com/cgi-bin/wt ... XJTU6&P=ML
ok so that one is 40$ and only has 100rpms
http://www3.towerhobbies.com/cgi-bin/wt ... XLWT1&P=ML
but then this one is 25$ and its 1380 rpms
and a lot smaller.

im guessing the first one has more torque?
which is good, but then is weighs a lot more.

http://www3.towerhobbies.com/cgi-bin/wt ... XLWT4&P=ML
im acually looking at this one to get


and another question is:
the first one i have on here is a whole different design.
and the other ones all have the drive shaft sticking way out there. kinda a pain in the butt to use on a foamie.

i am a noobie but not as much as you think.


any help would be grateful.

thank you in advanced.

P.S. i will get a picture of my old plane up here so you can get a idea of what i am doing. as far as being a "foamie"
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Old 09-22-2008, 05:37 PM
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eflight-ray
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I don't have any of those motors, so can only give a generalization.

The 3 motors current rating are 11A, 9A, and 17A in the order you have.

Obviously the last one has the capability of being the most powerful.

But it depends on what battery and what prop are used.

The kv number, the 1000, 1380 and 1600, refer to the rpm/volt. Usually the lower the kv number the bigger prop diameter the motor could turn, (but the amp rating is also a limiting factor).

It's difficult to generalize on which is the better motor, but if weight is not a very important factor, then a bigger more powerful motor will usually be better. You don't have to use the extra power, but if you do build a model that needs more power sometime, it save having to buy another motor.

One tip when flying, always fly up wind of yourself. If you do make a mistake and the model drifts back, it should still be easy to see, and the priority is to get back up wind or land.
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Old 09-22-2008, 11:30 PM
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FlatSpin
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ok so say i get the 1600 KV motor and the recommended props are
Propeller: 7x4S - 9x4.7S so can i use a 7X6 or 8X6.

i would presume i can but when both of the given props shown are low pitched props im not sure.


thank for the help/ information
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Old 09-23-2008, 03:16 AM
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Dr Kiwi
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Be aware that the 7x4 might be for 3s, but the 9x4.7 for only 2s... so depending on your pack, your props might work, but you'll need to check amp draw.
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Old 09-24-2008, 03:13 AM
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FlatSpin
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i use a 3-cell for sure.

thanks for the help
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Old 09-24-2008, 04:19 AM
  #6  
Rolling Thunder
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I can say from experience (the bad kind)to buy a wattmeter to check current draw.I burned up 3 motors before getting one
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Old 09-24-2008, 04:25 AM
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FlatSpin
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yea i have a watts up meter.
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