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Old Nov 02, 2009, 12:37 PM
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Long Beach, CA
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Motor windings. What's the difference?

In anwering the following question please do not confuse me by becoming involved in one of those long drawn out technocrat's/mumbo/jumbo debates that folks on here seem to love so much.

Question:

Construction wise, these two motors are identical, except for the winds.

First motor: AXI 2826/12 (more winds: KV 730).

Second Motor: AXI 2826/10 (fewer winds: KV 870).

Assuming the same airplane in all respects except for motor and prop choice.
To simplify matters (or at least limit the answers) I should add that the batteries used
in both circumstances are identical: 4s2p, 2000 (total 4000).

When and for what kinds of results would I choose one over the other?
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Old Nov 02, 2009, 12:43 PM
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United States, VA, Chesterfield
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The first motor will turn a bigger prop on less cells and will draw a bit more amps than the second motor on the same prop and battery. Given the same power (2 cells) the first motor has more resistance because of the more winds and turns slower with more torque (that is why you can use a bigger prop).

I would imagine using the first motor with a larger (9 or 10 inch prop) with 2 lipos would be a good start.

If need more power use the second motor with 3 cells (lower amps than No. 1) with a smaller prop (8 inch or so). Because you are sending in more current (volts) you can use less amps and smaller prop to get a watt rating a bit higher than no. 1.

It is confusing sometimes--I have to almost draw a picture!
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Old Nov 02, 2009, 12:56 PM
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Thanks Pat, but let me put a limitation on your answer:
I will be using the identical battery 4s2p (total 4000).
Now what?
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Old Nov 02, 2009, 07:44 PM
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Hi Henry,

I think I see where you're going with this, so let me answer your question with a question.

Why do they make motors in so many different winds? Why don't they all get together and just make one wind of motor.... say.... 2000 kV?
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Old Nov 02, 2009, 09:03 PM
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Come on Chuck. Gemmie a break!
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Old Nov 02, 2009, 09:09 PM
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Quote:
Originally Posted by Henry111 View Post
Come on Chuck. Gemmie a break!
Hi Henry,

Believe me, I wasn't trying to be funny or cute. I was really trying to pin down where you were on the scale. I didn't want to answer your question with something too simple if you already knew it, nor too difficult if you weren't quite there yet.

There's nothing wrong with not knowing why they make so many different kV motors. In fact, I'd venture a guess that a whole LOT of people don't know the benefits of selecting a motor with the right kV.

If you want to start there, we can (and we can make it easy too).

Chuck
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Old Nov 02, 2009, 09:23 PM
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Chuck, I like cars with a lot of low-end so I can get out of a jam in a hurry, come out of a trun in a hurry, and get up to speed in a hurry, but not necessarily go as fast as the other guys down the straightaway. And I have to make more pit stops for gas. And they pull big boats up hill better. That's also why I like Quarter Horses over Therobreds.
12 winds over 10!!!
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Old Nov 02, 2009, 09:33 PM
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Quote:
Originally Posted by Henry111 View Post
Chuck, I like cars with a lot of low-end so I can get out of a jam in a hurry, come out of a trun in a hurry, and get up to speed in a hurry, but not necessarily go as fast as the other guys down the straightaway. And I have to make more pit stops for gas. And they pull big boats up hill better. That's also why I like Quarter Horses over Therobreds.
12 winds over 10!!!
I go with Chuck.

We are wasting our time. There is a technical explanation, but if you don't want to spend the time to understand it.

AND you don't want to state what exactly you want to do, there is NO unique answer. Why bother?
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Old Nov 03, 2009, 03:28 PM
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C'mon Guys

This is an easy one to answer for the man. He has already stated same battery, same
type aeroplane etc.
By looking at the KV alone the situation is thus....the lower KV motor will swing a larger
prop to develop X watts. The higher KV motor on same battery will develop the same
number of x watts on a smaller prop because it is spinning the smaller prop faster for the same level of voltage (battery the same). one of the reasons why we have higher / lower
KV motors is such that we can match the prop to the plane (issue when there are ground clearance tolerances). There are also many other subtle technical issues but this
is a big reason.
Example, i have used a 800KV motor from good 'ol HK that has turned out to be wolf
in sheep skins. I run it on a .46 trainer with 5S lipo and 12x8 apc prop. It outperforms
a .46 two stroke by miles. I get big stares with this one! Point is i couldn't use
a 400KV motor because to develop the 1200W i am generating i would have needed
a 16" or 17" prop. Ground clearance does not allow for it.....
For those that are interested there is very little offered elsewhere that can compete
with this motor in the same cost/performance class. Truly a gem in the rough.....

Be good y'all
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Old Nov 04, 2009, 02:40 AM
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Quote:
Originally Posted by NUTSANDVOLTS View Post
C'mon Guys

This is an easy one to answer for the man. He has already stated same battery, same
type aeroplane etc.
By looking at the KV alone the situation is thus....the lower KV motor will swing a larger
prop to develop X watts. The higher KV motor on same battery will develop the same
number of x watts on a smaller prop because it is spinning the smaller prop faster for the same level of voltage (battery the same). Be good y'all
Good answer, I will add that every motor has a RPM limit and a current limit, and I am sure that 2826/10 will break some of those limits on 4 cells battery (12000rpm and 40A fror 2826/10). Means either too high current (with large prop too keep rpm low) or too high rpm (with small prop too keep current low) or both.

4 cells need minimally 12 windings on 2826
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Old Nov 04, 2009, 04:01 AM
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wow
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Old Nov 04, 2009, 04:45 AM
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its a lot simpler. If you take the why and how out and juts say what happens..

The hotter wind will develop more power at higher RPM and higher current on a smaller prop for the same 'hotness' of motor.

The smaller prop turning at high RPM will be less efficient.

At some point, there is a compromise decisions to be made
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Old Nov 04, 2009, 01:01 PM
Usual suspect.
St. Louis MO
Joined Feb 2007
945 Posts
First... the /10 is a 920Kv motor, not 870kv - A noticable difference in terms of amp draw on the same prop.

For sport or speed, get the /10 and a 12x8E prop to start with.
For 3D flying, get the /10 and a 13x6.5E to start with.
Check amps and swap props as necessary.

Either way... I'd go with a Hacker A30-10XL, or Torque 2812, or Reaper GR-45 instead of the AXI.
All three of them have higher power ratings, better prices, and come with all of the required mounting and prop adapting hardware.
The AXI will require a x-mount and prop adapter - sold seperate at $15
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