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Old Jul 18, 2003, 11:47 PM
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M-20 and N-20 Motor/Gearbox/Prop Test Results

Hey all - I've been running bench tests of various M-20 & N-20 motors, gearboxes and prop combos and posted a bunch of results at http://www.eflightdesigns.com/docs/motordata.html

I'll be posting some more results in the next couple of weeks - U80 props, direct drive M-20 LV and HVs, etc.

My thrust measuring rig is not, uh, ISO-9000 certified, so take those numbers with a grain of salt, but the numbers should be good for relative comparisons.

BTW-I especially like the Kenway 4.2:1 gearbox with the M-20 HV motor. Great thrust on a single Li-Poly at about 500ma - I'm thinking a DC-3 or P-38 twin would be really cool...

Hope someone finds the data useful!

Mike C.
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Old Jul 20, 2003, 04:03 PM
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Thanks, Mike.

Moderators, I'm wondering if we can't have another thread in the "Useful Threads" section which contains a compilation of the results of the motor tests that various members (and particularly Gordon) have published. People are often asking about these and it would be great to have them in one place.

-John
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Old Jul 20, 2003, 07:23 PM
DNA
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Interesting tests Mike, thanks for posting the link.

I have a question though. Is it better to have a motor producing 20gm of
thrust from a dd 3" prop at 8300rpm or is it better to have a motor producing
20gm of thrust from a geared 5" prop at 3000rpm?

I realize the size of the prop may depend on the model and the frontal
area of the fuse, but if you can eliminate the gear drive and get the same
thrust, why wouldn't you want to do that if the amps are within 100ma
of each other?

Btw, with all the various N20 motors available from Goldmine, All-Electronics,
Todds, Selman, American Science, GWS, etc, does anyone know for certain
which are LV and which are HV?
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Old Jul 20, 2003, 07:38 PM
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DNA - I think it pretty much depends on your speed requirements. A 3x3 prop turning 8000RPM will give you a higher pitch speed than a 5x3 prop turning 3000RPM - and therefore a higher flight speed on the model. So while the Kenway M-20 HV has almost the same thrust as others, the pitch speed is lower & will not fly a plane that needs speed to stay aloft.

I'm *pretty* certain that most all of the $2 and less N-20s are the low voltage version, and that they all probably came from the same source. The ones that say "8722 CHINA" for example are LVs. And since I've found places where you can buy these by the thousands (www.surplustraders.net for example), I figure that's what AllElectronics, Brigars, Goldmines, etc. of the world have done.

I think the GWS ones are HVs, though not 100% certain. I suppose I should go measure the resistances & see. Gordon might know off-hand.

Does anyone out there know if the "8722" on the motors are a date code, or are they the Mabuchi codes that identify the number of winds & poles?

Mike C.
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Old Jul 20, 2003, 09:02 PM
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I'd have to go look at some and maybe do some more research. But, I think you are right that the surplus ones are the LV. I believe that the differences between the N20-LV and N20-HV are not as great as the differences between the M20-LV and M20-HV. In other words, relative to their size, I think the M20-LV is a hotter wind motor compared to the M20-HV. I think the N20-HV is pretty much available from sources like DJ Aerotech and Kenway. The ones Todd sells are the LV. I've bought them from him and from All Electronics. I haven't bought the N20-LV from other sources than those two. The GWS may not be a genuine N20. There seem to be a number of companies that make N20 clones.

The geared versus DD issue is probably why Matt tested the motors and props for his P38 in a wind tunnel, to get more realistic measures.

Gordon
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Old Jul 21, 2003, 03:34 PM
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I bought ten N20LV motors from bgmicro.com, for $4.95 total. Single price was $0.79. They have the "CHINA 8722" imprinted on the body. The resistance is 2.3 Ohms. At this price, you could change a motor every few flights and not feel it.

I also have two other N20LV's I bought elsewhere for $2 each, with "CHINA 8618" printed. These motors are identical in look, feel and resistance to those above. Both motor types have a very small Mabuchi logo embossed on the backplate.

I guess the numbers may show production year and week - this is common practice in integrated circuit production.. I don't know if this holds for these motors, though.. In this case these two motor types would have been produced in different years..

It would be nice to find the N20HV or M20 types in this price range.. I never understood the reason for the huge price difference, maybe somebody bought the wrong motor and sold the batch real cheap to get rid of it..

Best regards,

Bulent
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Old Jul 21, 2003, 04:46 PM
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Quote:
The geared versus DD issue is probably why Matt tested the motors and props for his P38 in a wind tunnel, to get more realistic measures.
Yeah - certainly the static numbers don't tell the whole story. On paper a N-20 DD w/GWS 3x2 looks the same as a KP-00 w/85x45mm, but on an actual airplane, the KP-00 wins out every time (at least in my experience).

bmutlugil - I had suspected the numbers were a date code, and that pretty much confirms it.

BTW-I measre 1.8 ohms on the N-20 LV and 3.6 ohms on the motor from the GWS LPS-B2C gearbox. The GWS motor definitely looks different in a number of ways, so I think Gordon is right that it's not from Mabuchi.

Interestingly, at the Mabuchi Web Site if you search for "FF-N20" there is a "N20PA" rated at 3V and "N20PN" rated at 5V - so perhaps we should start calling the FF-N20PN (the common surplus motor) the "N20 MV" for "medium voltage"

As far as the cost difference goes - I'd guess that for some reason the factory produced a billion of these things, only to not find buyers (perhaps a buyer reneged), so they dumped them on the surplus market. And clearly enough were dumped to last a long, long time...

Mike C.
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Old Jul 21, 2003, 05:23 PM
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All the n20's out on the market are not of mabuchi origin. There are many, many, motor manufacturers in china that simply make copies of mabuchi's motors, often at a fraction of the cost. So there are plenty of copies out there. Motors of these type cost about 30-40 cents each in large enough quantities. I could probably import a whole bunch at about a dollar or so if I got enough promises from micro-flight distributors.

$7 for a M20LV bothers me

-Sean
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Old Jul 21, 2003, 10:40 PM
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I know someone who checked on the cost of M20's directly from Mabuchi. The cost was quite reasonable, but the minimum order was 10,000 units.

Interestingly the Chinese manufacturers who copy the N20 don't do the same for the M20. I have never found a clone M20. They might exist, but I haven't found one yet.

The GWS Pico servo motor is a clone of the Mabuchi K10 (smaller brother to the M20). The GWS version has a slightly hotter wind than a genuine Mabuchi (I have both). So, yes it makes sense that not all clones are the same as the equivalent Mabuchi.

Quite a while back the GWS CEO stated that the numbers on the motors were for date of manufacture. I think this was about the time they introduced their N20 sized propulsion system.

The small motors can be very confusing. How about this one? The newer KP00 motors seem to have winds equivalent to the M20-LV in the E-Charger planes. Genuine KP00 motors from two years ago had a hotter wind, pull more amps, and generate more thrust. Ken Basset of Kenway told me that there have been at least 5 different M20's listed in the Mabuchi catalogs over the past five or six years, but currently there are only two. So, various motor winds come and go depending on the needs of their customers. I would guess that K&P exhausted their supply of the older KP00 M20 and are now using the same one as the E-Charger.

Gordon
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Old Jul 21, 2003, 11:34 PM
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Gordon,

Very true. Often manufacturers require a slightly differerent winds. However the motor makers will supply all the info you want, and can tailor the motor to best suit your needs. But that requires a larger order for it to be worthwhile. Tooling to make motors is very expensive so this is why mabuchi will list many types of the same motors that they have the tooling for, in hopes that some other customers will want the same motor.

I can arrange to get particular mabuchi copies like the M20lv ,hv and n20 LV and HV. They probably wont have the exact characteristics as the mabuchi motors but testing samples can show how useful they are.

The question is though, how many motors does the micro flight community need?

-Sean
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Old Jul 22, 2003, 02:38 AM
DNA
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While a company like E-Chargers might buy 10,000 motors at a
time, I doubt if Kenway buys that many. There must be a distributor
around somewhere that Kenway buys them from.
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Old Jul 22, 2003, 04:45 AM
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Yes, but also at a higher price, hence the $7 for a M20-LV.

Gordon
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Old Jul 22, 2003, 05:57 AM
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I think Ken gets his LV motors from K&P like the rest of us. Not sure about the HVs.

Incidentally, the Megatech X-EC Diversion seems to have M-20 clone motors (different markings than a Mabuchi, and a shinier case).

Mike C.
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Old Jul 22, 2003, 07:45 AM
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The recent 2 cell LiPoly mods to the RFFS have me itching to try the HV M20, properly geared or proped to let it unwind. Jochen says, and he should know, that a higher volt (higher resistance) motor is more efficient. The only HV M20 I have comes from ToyTronix and measures 2.5 ohms vs the LV which is about 1.5. Does anyone have any measurements on a HV M20 from a different source? I think Kenway has one. I wish Ken would do a simple web site, It would be much easier to keep track of his products. He is one of the real pioneers of micros.

Dave
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Old Jul 22, 2003, 07:59 AM
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The Kenway one is 3.6 ohms. BTW-I carry much of Ken's stuff, so if you need a spec that you don't see on the site, let me know & I can probably find out.

Mike C.
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