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Electric motor numbers?

Old 01-06-2015, 12:35 PM
  #1  
davidchoate
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Default Electric motor numbers?

I a building a klemm 40" WS. Plan calls for a 2204- 19 Gold outrunner, and 8amp ESC. What does this translate to in Eflite? A 250 series, or 370? Is the 2204 the Kv rating? I have very good electrictrical knowledge, but need help deciphering all the number systems meanings of different manufacturers. Thanx.
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Old 01-06-2015, 12:37 PM
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davidchoate
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Default Gold 2204-19 outrunner

What is a a Gold 2204-19 outrunner's equivalent in an Eflite motor?
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Old 01-06-2015, 01:25 PM
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JetPlaneFlyer
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22 is stator the diameter, 04 is stator the length, 19 is the number of turns


None of this helps much with comparing to other motors that use different naming conventions, but if you look for an outrunner motor in the 20-25g weight range and in the ballpark of 1400Kv you will be in the right place. The eFlite Park 300 would do the job but there are plenty of choices.
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Old 01-06-2015, 01:37 PM
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fhhuber
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Some makers the numbers are overall motor dia X length and winds... such as Turnigy's 2826/6 at appx 55 grams motor weight
Some the numbers are stator dia X length and winds... such as Cheetah's 2826/6 at about 175 grams motor weight
And some seem to just pull numbers out of the air....

You can only depend on comparing the numbers with another motor of the same brand and then only if they use one of the numbering schemes that makes at least a little bit of sense
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Old 01-06-2015, 02:50 PM
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solentlife
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I find annoying the differing conventions ... as "fhhuber" indicates - some use one set of dimensions .. some another ... some use the Parkfly rating - which means absolutely even less to someone like me !! Some use the weight ... some even use the 'glow-engine size' equivalence ... such as G46 .. G60 etc.

I've given up on the conventions most motors and now go through the data specs on them looking for amp / volts, prop size and rpm figures .. That at least should be a good indication of which to use where !

Nigel
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Old 01-06-2015, 03:08 PM
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fhhuber
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If you are used to glow engines... the glow equiv numbers will just make you confused. They have no relationship at all to the ability to swing the same prop the same rpm as the indicated glow engine size.
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Old 01-06-2015, 03:17 PM
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solentlife
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Originally Posted by fhhuber View Post
If you are used to glow engines... the glow equiv numbers will just make you confused. They have no relationship at all to the ability to swing the same prop the same rpm as the indicated glow engine size.
The problem as I see it ... I have pals who fly the G series motors and I have to say they run very nice !... is they are more related to 4 stroke performance than the average 2 stroker.
So seeing those - I would suggest keeping to that and it will not be too far out.

Nigel
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Old 01-06-2015, 10:15 PM
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davidchoate
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Thanx guys. Another question. I have a Eflite 4100kv inrunner in a 6.6:1 gearbox. I understand that kv is rpm x 1000 per volt. Is this right? Its a park 370 inrunner. I want to use it on a 40" Ws Swallow (Klemm) Auw 325g's with a 8x3.5 slowflyer prop. Is this O.K., or should I just use the 370 outrunner. ? Also if I use the geared motor; what battery is good. I have a 1300mah Eflite 2 cell, or a 3 cell 11.1v 850mah. I plan to use a 18 A ESC, but I think its a bit much,and The full scale plane had a very small engine, and so does not require alot of nose weight to balance. The plans recommend a 300 series motor I assume. I do have a 10 Amp Eflite ESC. My Tx is a Spektrum DX6i, and so I can program the Esc easier. IThis is My first larger Plane, although still a Park Flyer. Until now I have been converting Guillows Planes to RC. I usually use 1 150 series, and super micro servos on them. I got that formula down after 3 years, and learned alot, but it's not My lack of understanding electrical theory ( I am a Auto Mechanic 30 + yrs., and am very good at electrical stuff. It's just that I got back into the hobby after 35 years, and used glow engines, and need education on these motor sizes, and terminology etc...
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Old 01-06-2015, 10:26 PM
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Default Swal motor choice. loow

According to plan; The AUW should be 12 oz. I came in about 50g's under that. It has 125 sq. in. of wing area. I read that the RAF used to remove the engine, and use them to train Glider pilots, and it's My first aileron Plane as well. I want to learn on this before I take My Stearman I spent a year building for its Maiden. Do You think an Eflite park 250 with a 8" Slowflyer would handle this without having to bury the throttle to keep it aloft? Thanx for any advice. I have not flown My test plane yet. AUW 200g. I put a HURC (Heads UP RC 250, and 10 a ESC on it. It was fine with a 6040 GWS prop, but when I tried a 6" 3 bladed prop it went inti 'soft' mode. Any Explainaition?
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Old 01-07-2015, 05:30 AM
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hayofstacks
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I use heads up a ton. I look for the proper prop size and thrust mainly. At 200 grams, that's about 7 ounces. Id see how tail/ nose heavy the plane is with intended battery, add lead until you come up with good balance, then pick a motor close in weight to what you need.

Its really a matter of preference, but i like well over a 2:1 thrust to weight ratio, but most of my planes have been in the 1:1.5 range, which is really easy to accomplish if you need any nose weight.
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Old 01-08-2015, 03:02 PM
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davidchoate
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Default Thrust to weight.

There'a a thread in here by a Guy called "Nofly", and he explained motor,prop, and how to figure out stall speed Etc.. wonderfully. You should check it out.
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Old 01-08-2015, 06:48 PM
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Rockin Robbins
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Originally Posted by davidchoate View Post
I understand that kv is rpm x 1000 per volt. Is this right?
Missed by it THAT much! Kv is the number of rpm the unloaded motor (nothing on the shaft) will turn per volt applied. This is supposed to be a mathematically calculated number worked out from the electrical properties of the motor. As the motor spins from voltage applied, the magnets generate an opposing current (called back EMF) which opposes rotation. There is a rotational speed where the back EMF balances the voltage applied and that rpm is the Kv number when calculated for one volt. Because there is inherent friction in bearings the actual measured RPM per volt applied will be a tiny bit different from the calculated number.

Motors wound with few winds around the stator don't generate as much current as motors with more winds. So you might see a Turnigy 2217-20 860 Kv motor and you would see a 2217-6 1800 Kv motor. In the Turnigy world the number after the hyphen is the number of winds around the stator. And you can see that the fewer winds the higher the Kv number.

So if you take the 2217-20 860 Kv motor and apply 11.3 volts from a 3S LiPo pack you'll get about 860 x 11.3 = 9718 RPM. Once you hang a prop on there your RPM will be less because the back EMF is reinforced by the rotating resistance of the propeller.

A low Kv motor is like a truck engine, producing gobs of low RPM torque but little top end speed. A high Kv motor is like a sports car motor, not so much torque but lots of top end. They might both produce the same amount of power (measured in Watts with electric motors), but their characteristics will be very different.
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Old 01-09-2015, 03:31 PM
  #13  
davidchoate
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Default kv

now I understand why My eflite 4100kv inrunner needs a gearbox.
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Old 01-06-2023, 12:40 PM
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ddlawrence
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I have a general rule for sizing motor power of 100W per pound of airplane. That will give great aerobatic performance, but not enough for hovering.
They say you can go as low as 50 W per pound for trainers.
To size the prop, the motor manufacturer will usually recommend a range of prop sizes to choose from.
Then get an ESC that is rated for more current than the motor rating.
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