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Old Jan 12, 2013, 10:20 AM
Lee Liddle
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Carrollton, Tx
Joined Dec 2006
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4kw+ Motor for 70mm-80mm Fans....Powered by a 39mm inrunner see Post #383

A 9 tooth 6 pole Custom High RPM 42mm Outrunner

The line above is the short story, but there`s a lot more to it for those who are interested.

Many in the EDF forums know that I have added a 36mm dia outrunner to a cut down 75mm Haoye 7 blade rotor and a 70mm shroud to build a very high powered 70mm fan. It`s a beast, but it`s limitation has been the 8 pole bell. With most, if not all ESC this means an upper RPM limit of about 50k. Since most real HiPo 70mm fans operate above that level, the 8 pole design was a problem.

Many 28mm and smaller outrunners use a 9 tooth 6 pole design that increases the RPM limit up to about 70k. That would be great for most 70mm fans, but my year long search for a 36mm outrunner with 6 poles has come up empty.


. New development... there are several 9/6 36mm to 42mm motors available. Right now (2/25/13) I'm working with the Turnigy T-500 Helidrive which is 42mm in dia. That's about the largest dia that might work in a 70mm fan. Also it should be great in an 80mm. So if you are just reading the thread for the first time, skip all of the 4pole experiments and move to the work done with the Helidrive motor. The first post regarding this motor is #223

So, what do you do? First, I adapted the 75mm Haoye rotor because it is strong and has 7 high pitched blades. This has given some awesome power at under 50k rpm, but how much more performance is out there? I want to find out.

There are other high load rotor options, but they have their own issues. So far, the plastic high blade count rotors can`t hold together above 50k for very long, so they are out. The other option is the metal rotors. They will probably work, but I have a problem paying hundreds of bucks for a 70mm speed fan when my 7kw big fans only cost me about $80 for the parts.

What I really wanted/needed was a 36mm outrunner with less than 8 poles. Since I couldn`t find one, that only left one solution, try to build one.

This morning, after about 20 failures, I have just completed my first successful preliminary run tests on a 12 tooth, 4 pole motor. Needless to say, I`m very excited about it.

Why is it a game changer......

1) The basic parts needed only cost about $30 or so.
2) It can be used to power fans as small as 64mm
3) It can handle sustained power levels over 4kw
4) It`s rebuild-able and the kv can be tailored to desired levels
5)Lower cost ESC that have only 16k pwm can be used
6)With lower kv, HV and even SHV can be used, again only 16kpwm is needed
7)The added cooling of the motor in stand-off makes high amp/lower volt combos with 6s ESC a practical solution also
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Old Jan 12, 2013, 11:15 AM
Lee Liddle
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Carrollton, Tx
Joined Dec 2006
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Well, I`ve just run the prototype motor, unloaded, at 65k rpm on 7s on a $20 Suppo esc with just a 16k pwm processor. The motor ran very smoothly.

There is still lots of work and experimenting left to do, months or years worth.

This opens up the entire line of small fans to 36mm outrunner power at rpms up to 100k and with the use of many inexpensive esc types from 3s on up to 14s.

In the next few weeks, after I have done some actual loaded testing in a high rpm fan, I will complete the thread by showing exactly how to build the motor. It`s really not that hard. The magnets have to be removed, rearranged, and some additional magnets added. Then, the stator has to be rewound, but it is a very simple winding pattern, that anyone should be able to duplicate.

All of the needed parts can be ordered from normal suppliers. Just building one motor might cost $60 or $70, but then you`d have the parts to build 2 more for an extra $20 each. That would bring the cost for a single unit down to about $35.

So stay tuned for further developments, pictures, and eventually some video.
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Old Jan 12, 2013, 11:36 AM
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MVP Award

I nominate Lee for RC Groups MVP!
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Old Jan 12, 2013, 11:42 AM
Lee Liddle
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Carrollton, Tx
Joined Dec 2006
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Some motor formulas

Some motor formulas and the resulting kv........

10.5 turns of 22 gauge = 1750kv ( 21 gauge would fit for sure, 20 gauge maybe)

14.5 turns of 22 gauge = 1150kv (might squeeze 15.5 turns of #22 on it)

A few pics of the magnet configuration
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Old Jan 12, 2013, 12:36 PM
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Yeah, Lee!

On the mark! Can't wait for your tutorial on this - got a real need for this.

Thank you for your persistence, amigo!
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Old Jan 12, 2013, 12:56 PM
DELTAS RULE
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dude thats a awesome idea!!!! i winder why nobody has tried that yet!
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Old Jan 12, 2013, 01:08 PM
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Interesting, you would think that the wider magnet would make a three times larger pulse width in the windings because of the wider magnetic field. Does it affect the ESC timing very much? Did you try it with 4 single magnets equally spaced? Two magnets?
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Old Jan 12, 2013, 01:24 PM
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I didn't want to be the person to say its a silly idea. But I feel I should warn you that what you're trying to do is dangerous. Those small magnets will weigh 100's of kg at 100k and that's alot of centrifugal force on that thin aluminium bell. Motors do have physical limits.

A 70mm fan at 100,000 puts the tip speed just over the speed of sound which isn't good at all for efficiency.

I'm honestly shocked you guys have been getting away with pushing 28mm motors beyond 60k. Let alone trying to push 36mm OUTRUNNERS to 100.
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Old Jan 12, 2013, 02:05 PM
Lee Liddle
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Quote:
Originally Posted by SlowBarless View Post
I didn't want to be the person to say its a silly idea. But I feel I should warn you that what you're trying to do is dangerous. Those small magnets will weigh 100's of kg at 100k and that's alot of centrifugal force on that thin aluminium bell. Motors do have physical limits.

A 70mm fan at 100,000 puts the tip speed just over the speed of sound which isn't good at all for efficiency.

I'm honestly shocked you guys have been getting away with pushing 28mm motors beyond 60k. Let alone trying to push 36mm OUTRUNNERS to 100.
Well, there is no need to run a 70mm fan at 100k, my point is that 100k will be the new electric limit based on a 16k pwm esc.

As far as physical limits go, everything has them. The Nina, Pinta, and the Santa
Maria also had physical limits. They were only designed to sail on a flat Earth.

But, let me add, thanks for the warning and safety concern. I will be careful, and use appropriate safety measures.
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Old Jan 12, 2013, 02:38 PM
I am actually really slow
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Quote:
Originally Posted by Knife Liddle View Post
Well, there is no need to run a 70mm fan at 100k, my point is that 100k will be the new electric limit based on a 16k pwm esc.

As far as physical limits go, everything has them. The Nina, Pinta, and the Santa
Maria also had physical limits. They were only designed to sail on a flat Earth.

But, let me add, thanks for the warning and safety concern. I will be careful, and use appropriate safety measures.
Glad you agree there's no need to push a 70mm that far. I think if anyone wants to they should be buying a turbine.

Maybe you could look at wrapping the bells in carbon rovings and then rebalancing them. If you have access to a lathe you could do a really nice job of it and atleast that way you wouldn't have to worry about the bell going pop at high rpm.

I'm also a newbie when it comes to ducted fans. But I'm wondering why not use a 15xx or 14xx neu motor which is 4 poles instead of modifying an outrunner? Are the Neus slightly to large?
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Old Jan 12, 2013, 02:47 PM
Lee Liddle
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An inrunner could work if the shaft was long enough. It takes a long shaft or a custom adapter to mount the motor behind the fan, and 36mm motors have to be mounted that way. So you could order a custom motor from a manufacturer, but Id hate to think what the wait would be, let alone the cost. And if the kv turned out to be wrong, you'd have a very expensive paper weight.
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Old Jan 12, 2013, 04:14 PM
Lee Liddle
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Carrollton, Tx
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My relativly uneducated Theory

Quote:
Originally Posted by rfodor View Post
Interesting, you would think that the wider magnet would make a three times larger pulse width in the windings because of the wider magnetic field. Does it affect the ESC timing very much? Did you try it with 4 single magnets equally spaced? Two magnets?
Well sometimes my ignorance, not knowing why something might not work, frees me to discover something that works even when when it shouldn`t work.

Right now the esc is set for 15 degrees timing which works well at 65k. I still have a lot of testing and esc settings to try.

Here`s why I think it works. For a six tooth/ 4 pole motor there is an accepted winding pattern, but to use it on the 12 tooth stator would require leaving 6 teeth empty. That wasn`t acceptable because the reduces copper would limit the power that the motor could handle.

Basically, what I`ve done is wind the stator like it is two 6 tooth stators in the same place. I wind tooth #1 and then wind tooth #2 the same way, then continue to tooth #6 and #7, that`s phase A.....and so on. This fills up the stator. My theory/hope was that this would act just like a 6 tooth stator with big fat teeth.

So I figured I`d need big fat mags to match. Also, I have read that you need as much mag coverage inside the bell as you can get, and that side by side mags that are oriented the same act as a single mag. I tried just using 8 mags and leaving all of the gaps the same, but that didn`t work. Filling in the gaps with a smaller mag was the magic that made it work.

There is a winding pattern for a 3 tooth 2 pole motor. The same method might work, by winding 4 side by side teeth as a single tooth, and "building" just two massive mags, one N and one S. But, since the 4 pole motor will meet my needs of using 16k pwm esc at up to 100k rpm, I don`t see any need for a 2 pole motor, and my gut feeling is that the 4 pole motor will run more smoothly and do everything that I need it to do.
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Old Jan 12, 2013, 04:15 PM
Lee Liddle
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Carrollton, Tx
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Quote:
Originally Posted by corsair nut View Post
dude thats a awesome idea!!!! i winder why nobody has tried that yet!
Probably because they wouldn`t sell thousands of them.
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Old Jan 12, 2013, 04:20 PM
Lee Liddle
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Carrollton, Tx
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Originally Posted by PikeStaff View Post
On the mark! Can't wait for your tutorial on this - got a real need for this.

Thank you for your persistence, amigo!
You are welcome. It may take me a little while, life stuff you know, but I will get it done and show how to duplicate my efforts. I want to take a little time to make sure that it works as well as it seems to, before I get others directly involved.
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Old Jan 12, 2013, 08:16 PM
Life begins at transition
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Lee,

Hopefully this helps:


I know Ralph Okon with a Scorpion in 12n4p, but since he's blown his website away, I can't find any info on it any more Shame, the man does excellent work.

I've done a couple of 12n4p for smaller (30mm) fans, and found them to be ineffiecient, but capable of 80+krpm. It was a massive trade-off between 50krpm at reasonable efficiency, or 80k at horribly low. But hey - you go fast, you burn lithium
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