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Mar 01, 2006, 03:01 PM
Retired CAD guy
birdofplay's Avatar

need rules of thumb

I am wondering if there is a "Rules Of Thumb" chart
or speadsheet somewhere ?
I have not discovered it yet and I've been looking
and searching for some time.
I know all of the info is here already but it has to be
gleaned from zilllions of posts. ( just lazy I guess )

I have 2 ea Komodo 278 v2 and 2 ea 283 v2 motors.
I have built one of each and without spec-ing them
they seem to be quite powerfull and fun to build.
I was pleased with the kit quality and docs.

Now I want to "Play" with the second of each motor to
investigate performance potentials BUT I dont want to
waste too much Time and or Wire or especially $$$,
hence the Rules Of Thumb quest.

While I do appreciate all the "background",
this chart would be an attempt to cut thru the myriad
of engineering stuff.
Hey, Spring is fast approaching in the Northern hemisphere
and I want to be ready to fly something as opposed to
Stuck indoors reading all of the wonderfull posts in this forum.

The chart would be sort of a summation of
Theory vs benifits of changes to
Stator size ( yeah yeah - bigger is better )
Stator numbers

For instance if a typical stator size was selected,
say a 23.8 mm, then what would be the effect of
various changes around that same stator.
i.e. - assuming everything else constant
More or less turns -> ?
More or less magnets -> ?
More or less magnet strength/size -> ?
hook up differences Y vs delta vs ?

I'm loooking for A Cook Book as opposed to a Chemistry lesson.
Or in this case, an electronics lesson.
I believe for some folks, building motors is a means to an end
as opposed to the passion of engineering itself.

Another question is re In runner vs Outrunner.
With out wishing to incite a war of words
I had read yrs ago when Outruners were just coming out
that THEY were more efficient due to the magnet
placment geometry.

In the forum I have seen comments stating that
outruners are not as efficient as innruners.

Is my confusion over "Types" of efficiency ?
as opposed to overall/system efficiency.
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Mar 01, 2006, 03:45 PM
Registered User
radfordc's Avatar
There are a few "simple" rules:

Magnets. Most motors use 12 magnets. If you use 6 magnets, the Kv of the motor will double. Stronger magnets give more torque but lower Kv.

Wye vs Delta. For the same number of turns of wire, Delta will give 1.7 times more Kv than Wye. Delta also draws 1.7 times more current under equal conditions.

Number of winds vs size of wire. More turns of wire will give lower Kv all things being equal. You want to maximize the amount of copper on the stator. This means that you should use the size wire that provides the most "filling" of the stator for the given number of turns.

Stator size. Larger diameter stator will give lower Kv. Thicker stator will also give lower Kv.

In general, lower Kv motors turn slower at lower amp draws and are good for large props direct drive. Higher Kv motors turn faster at higher amp draws and are good for small props direct drive or for large props with a gearbox.
Mar 01, 2006, 04:15 PM
Registered User
radfordc's Avatar
Strong R/C provided this info:

This chart is for the stators sold by GoBrushless and used in "stock" cans. The 22.7 stators can usually be wound full. The 20 mm stator windings are often limited by the small space between the can face and the stator, which prevents adding enough turns to fill the slots.
Mar 01, 2006, 05:49 PM
Registered User
Go to the Komodo site, click on "tutorial download", there's performance data for different winds there.

Good Luck!
Mar 01, 2006, 07:03 PM
Retired CAD guy
birdofplay's Avatar
Thanks guys :-)

re magnets ...

Um , lets say I wanted Higher KV so I go to 1/2 the magnets.
I assume that I have to pull all 12 then re do NSNSNS equally spaced.
Should I double up or does that fall under the Stronger magnets = less Kv rule ?
Or would I actually just need to buy larger single magnets ?
Mar 01, 2006, 07:19 PM
Flying chia pet
chia_pet_farmer's Avatar
Doubling up works great: NNSSNNSSNNSS. It does not fall under the "Stronger magnets = less Kv" rule because it's the number of poles that count, which you are decreasing to 6 when you double up.

If you can find larger single magnets go for it. But my guess is that they would have to be curved because a single larger magnet would not conform to the shape of the bell as well as 2 smaller magnets.

- Mark
Mar 01, 2006, 07:30 PM
Retired CAD guy
birdofplay's Avatar
Thanx Mark

I guess I'mm gonna fool with Delta va Y and then
have a go at the 1/2 magnets thang
and then
sometime later
try some different winds and gauges

Oh !! just as it hit the post button on the previous post
I wondered - these are pretty strong magnets
arent they gonna be TOUGH to get close to each other
when doubling up ?

Ok Enuf for now :-) L8r
Mar 01, 2006, 08:14 PM
Registered User
Don't go to 6 poles unless your controller won't handle enough speed. You're better off with fewer, heavier winds to get speed.

Good Luck!
Mar 01, 2006, 09:53 PM
Registered User
radfordc's Avatar
You can usually use six magnets NSNSNS. No need to use 12 magnets in NNSSNNSS... config. Sometimes using the additional magnets actually makes the motor run worse.
Mar 01, 2006, 10:31 PM
Retired CAD guy
birdofplay's Avatar
OK - Kewel - Thanx

I have a coupla new T-bird 9 and an 18 ESC's
we'll hafta see how they handle it.

news as it develops ;-)

Mar 02, 2006, 12:01 AM
Flying motor mount master
fly_boy99's Avatar
You mean don't go 6 poles unless your controller can handle the higher rpms as well the higher rpms draw alot higher current as well.

Look at the Mega Beater thread for some good tips on these setups.

Originally Posted by BeavrdamElectric
Don't go to 6 poles unless your controller won't handle enough speed. You're better off with fewer, heavier winds to get speed.

Good Luck!
Mar 02, 2006, 01:58 AM
Registered User
With 6 poles, the controller can handle twice the RPM. But unless you run out of RPM with 12 poles, you'll be better off. The motor will be more efficient with lower resistance.

Either way, you need amps to make power.

Good Luck
Mar 02, 2006, 09:20 AM
Registered User
radfordc's Avatar
I recently needed a small high Kv motor for a helicopter. I built a 20mm motor with 12 magnets and Delta configuration. The motor drew more amps than it should. I changed to Wye config and changed to 6 magnets and now the motor runs well, low current and high Kv.

Here is a pic of the JGF 400DH motor. Notice how the six magnets are arrayed. The manufactuer tried adding six more magnets in NNSSNNSS configuration and found that the amp draw and heat increased dramatically with no increase in power. Sometimes simpler is better.

Mar 02, 2006, 12:37 PM
Retired CAD guy
birdofplay's Avatar
Yeah - This is the kind of discussion I like ...

Cause and effect without the math :-)
Mar 02, 2006, 04:30 PM
Flying chia pet
chia_pet_farmer's Avatar
I recently needed a small high Kv motor for a helicopter. I built a 20mm motor with 12 magnets and Delta configuration. The motor drew more amps than it should.
How many turns? Delta configuration is equivalent to 1.73 turns less than wye. If your number of turns was low enough, a delta termination would've caused the excessive amp draw. Otherwise, a 6 pole 12 magnet configuration does not necessarily correlate to higher amp draw.

- Mark

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