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Old Oct 08, 2008, 01:35 PM
rc-conk is offline
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which type of engine is better high kv or low kv


hi
i was wondering what the difference between 2 motors are
say i had a low kv electric motor turning a big prop
and a high kv motor turning a small prop
which would be best for a helicopter and plane
if i was using 2
thanks
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Old Oct 08, 2008, 01:37 PM
fly_boy99 is offline
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Heli's are geared so folks use higher Kv motors for smaller heli's up to say 450 class. As you get into larger heli's you will start using lower and lower Kv because of the gearing.

Planes can go either way, low Kv for 3D types and high Kv for faster planes.

Hope that helps,
B
Old Oct 08, 2008, 01:38 PM
Dr Kiwi is offline
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High Kv for helicopter since you are going to gear it very low.

For a plane it depends on the type of aircraft: low Kv/big prop for 3D, kigh Kv/small prop for fast pusher jet.
Old Oct 08, 2008, 02:39 PM
abenn is offline
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Most of my fixed-wing models are e-conversions of glow models, from about 5lbs to about 9lbs flying weight. In these I use motors with kv of around 800 or less, which results in a prop size roughly the same as I was using with the glow engines. Motor power, of course, depends on plane weight and the type of flying you want to do.
Old Oct 08, 2008, 04:14 PM
Alan Hahn is offline
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Quote:
Originally Posted by rc-conk
hi
i was wondering what the difference between 2 motors are
say i had a low kv electric motor turning a big prop
and a high kv motor turning a small prop
which would be best for a helicopter and plane
if i was using 2
thanks
For the plane it doesn't matter. With a low kV motor, choose a high cell count pack, and for the high kV motor use a low cell count pack. In these cases you can use the same size prop.

So for example, 1500kV motor, use 2s pack, for 1000kV motor use 3s pack. Prop size (same for both) needs to be chosen in this example to give a static rpm in the 8-9000 rpm range if you want either to run reasonable efficiently. Efficiency is the same, assuming both motors are wound with the same total weight of copper.

The 2s system will draw more amps and may need a bigger ESC for that reason, but motor efficiencies will be the same (this is about the 5'th time I have typed this, and I am only one of many who try to point this out.)
Old Oct 08, 2008, 04:15 PM
Mark Wood is offline
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Quote:
Originally Posted by fly_boy99
As you get into larger heli's you will start using lower and lower Kv because of the gearing.
Nope. You'll use lower Kv because you will use higher cell count batteries to drive the voltage up keeping the amp draw down.

mw
Old Oct 08, 2008, 04:19 PM
fly_boy99 is offline
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Depending on your gearing.....

Can't run higher cell counts on a higher Kv motor because your gearing is 1.2 to 1.

Show me a Large Heli which is not geared...

Quote:
Originally Posted by Mark Wood
Nope. You'll use lower Kv because you will use higher cell count batteries to drive the voltage up keeping the amp draw down.

mw


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