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Reformed Nitroaddict
07-19-2005, 11:25 PM
Okay - so the industry standard, or lack therof, for brushless power comparisons baffles me. I am running Himax motors in my planes, but would love to see a comparison to other brands before I buy my next motor to go in my upcoming Stevens Aero plane.

Is there anywhere on the web that gives a comparison of amps/watts/voltage ect... of various BL motors?

Mike Parsons
07-20-2005, 01:38 AM
There is a website that has quite a bit of motor comparisons. I will see if I can find it. Great information. Think it was called the Great motor test or something like that.

-Mike

Reformed Nitroaddict
07-20-2005, 01:21 PM
Please - that would be very helpful in deciding on new motor purchases.

Mike Parsons
07-20-2005, 06:54 PM
Here you go :)
http://www.flyingmodels.org/motortest/index_e.htm

adam_one
07-25-2005, 10:05 PM
You might also wish to check out the following site:
http://adamone.rchomepage.com/calc_motor.htm

Jason T
07-26-2005, 01:09 AM
adam_one,

Welcome to Wattflyers!

adam_one
07-26-2005, 06:02 AM
adam_one,

Welcome to Wattflyers!
Thanks! :)

Matt Kirsch
07-26-2005, 04:53 PM
It's not that the motor manufacturers are evil and withholding information to gain power over the masses... They would absolutely JUMP at a simple metric by which they could claim that their motor is better at all the rest.

The unfortunate truth is, there's no simple way to compare two motors unless they're nearly identical. That is, similar rotor length, similar rotor diameter, same design (inrunner/outrunner), similar mass.

There's only one way to make it easy: All manufacturers would have to agree on a set of specific motor designs. Basically, they'd all be making the exact same motors. The problem with this is that for all intents and purposes, the motors would all perform identically. You'd see minor differences in RPM and efficiency due to the quality of materials and manufacturing, but only minor.

When you compare glow engnies, you're comparing a complete power system. A motor is just one piece of an electric power system, the equivalent of the crankshaft in a glow engine.

To say that the information at flyingmodels.org is a motor comparison is a misnomer. It's a POWER SYSTEM comparison. Just by looking at the charts and comparing them, you can easily see that there is lots of "crossover" where two different motors will basically be doing the exact same thing. So, which one is better in that case from a "performance comparison" perspective? They're both offering the same performance...

Do not get me wrong. Sites like that are TREMENDOUSLY useful. The charts show you what combinations work, and how they perform. This is scads better than blind trial and error, especially when the motor manufacturer doesn't provide its own application charts. If I know what the plane needs as far as Watts and prop diameter, I can jump on a site like that and easily find at least one combination that will do the job.

Reformed Nitroaddict
07-26-2005, 05:05 PM
Matt - Basically what I was looking for was a way to compare motors and have it shown that at peak operating performance each motor would produce how many watts of power and how much thrust on an identical prop.

For example - I know that my Himax 2808-860 outrunner can turn a 9x6 prop at full throttle on 11V and it produces 8.5amps. This is listed in a chart on their website. So, in the most simplest sense, this motor will produce roughly 93.5watts of power. Now, if I were to want a motor that produced slightly more watts, say 120-145watts on 11V because of a slightly heavier model - how would I find out which motors are my best choices other than simply asking around?

Matt Kirsch
07-26-2005, 05:39 PM
You've got all the information you need right there: 120-145 Watts on 11V (a 3S LiPoly). From the Watts=Volts*Amps equation you can figure out that to get 145 Watts on 11V, you need a motor that can handle around 13 Amps.

All motors are rated by maximum cell count and maximum current, so it's relatively easy to find motors that can handle this kind of power. The hard part is coming up with a gearbox/prop combination that gets the power to the prop, and this is where flyingmodels comes in extremely handy.

Reformed Nitroaddict
07-26-2005, 06:17 PM
flying models?

Matt Kirsch
07-26-2005, 07:22 PM
Yes, the website Mike Parsons posted earlier:
http://www.flyingmodels.org/motortest/index_e.htm

stanger89
08-08-2005, 06:14 PM
The hard part is coming up with a gearbox/prop combination that gets the power to the prop, and this is where flyingmodels comes in extremely handy.

This is also where programs like motocalc come in handy. You can try different props and prop/gear combinations and see how they compare. Just be careful because these programs can give you combinations that would be imposible in real life.

JWN
08-10-2005, 05:27 AM
There is one problem with the rule of simply using watts and amps to determine if a motor will provide the desired performance and that is the kV rating. Two motors with different kV's will perform differently with the same prop even if they are running at the same wattage on the same battery. For me personally, this is where I start scratching my head. How can I be sure that XXX motor will do what I want it to in YYY airplane? Glow engines have the same problem because so some degree as very few manufacturers will tell you what rpm their engine will turn a specific prop on a specific fuel, much less the specific port timing, port size and volume or combustion chamber shape. (Not that this would matter much as few people understand how all of these variables interact with each other.) However, there are review we can read and other members in our local clubs we can ask who have most likely seen a particular engine in action. I have a feeling that until e-flight becomes as mainstream as wet power, we're going to have to ask lots of questions of those who have already done what we want to do, or experiment on our own a bit using tools such as motorcalc to help us at least head down the right path to our desired destination.

I foresee having a fairly large collection of power components by the time I'm as familiar with them as I am a good old fashioned glow plug engine.
John

stanger89
08-10-2005, 03:12 PM
There is one problem with the rule of simply using watts and amps to determine if a motor will provide the desired performance and that is the kV rating.

But you use watts, and from that amps and volts to pick a motor, or more accurately, to filter your choices. Watts is what flies the plane, so that's what you start. Watts to electrics are like displacement to "gas" airplanes. Say you have a gas plane that's designed for a .46 (eg my Somethin' Extra). They say .46 because it requires a power system of that "class" to fly. There are of course options, you could put a hot .46, or a cheap .40 the performance will be different.

Converting that to electric, you need something like 500W to fly it. Though I'd build it hot (eg a hot .46) so I'm aiming for more like 700W. You could look at it this way, a .46 will put out something like .7 HP. 1hp = 746W, so that comes out to be about 500W to fly the plane.

Two motors with different kV's will perform differently with the same prop even if they are running at the same wattage on the same battery. For me personally, this is where I start scratching my head. How can I be sure that XXX motor will do what I want it to in YYY airplane? Glow engines have the same problem because so some degree as very few manufacturers will tell you what rpm their engine will turn a specific prop on a specific fuel, much less the specific port timing, port size and volume or combustion chamber shape. (Not that this would matter much as few people understand how all of these variables interact with each other.)

This is where reviews, application charts, and simulators come in. Once you've figured out your power requirements, and filtered your motor selection, you look at charts, run them through Motocalc (or similar) to figure out what combo may work best.

JWN
08-10-2005, 08:18 PM
But you use watts, and from that amps and volts to pick a motor, or more accurately, to filter your choices. Watts is what flies the plane, so that's what you start. Watts to electrics are like displacement to "gas" airplanes. Say you have a gas plane that's designed for a .46 (eg my Somethin' Extra). They say .46 because it requires a power system of that "class" to fly. There are of course options, you could put a hot .46, or a cheap .40 the performance will be different.

That is exactly correct and is where the problem lies. Watts is generally looked at the same as HP is in an engine. But, just because a .91 ducted fan engine puts out 5+ HP, does not mean it is suitable to fly a 30 lb. P-51. In fact, I'd be surprised if that .91 could even taxi the model around where a gas engine would have no problem yanking it all over the sky. Because of this, you cannot rely on watts alone to determine what motor you should use for a given project. Using the ducted fan example, there are several 1000 watt ducted fan motors running around that couldn't get a small prop driven model off the ground.




This is where reviews, application charts, and simulators come in. Once you've figured out your power requirements, and filtered your motor selection, you look at charts, run them through Motocalc (or similar) to figure out what combo may work best.


That is exactly my point. It's not as easy to pick a power system as it is to pick a glow engine, for the majority of us. This is compounded by the huge selection of motors currently on the market. This selection is not bad, it's quite the opposite. I've looked at the specs for literally hundreds of different motors and am 100% convinced there is a solution available for any type of model and any level of performance desired. Determining what that solution is however, is not always as easy, or inexpensive, as it can be with a glow engine.

Don't take me the wrong way. I'm very interested in learning this new aspect of the hobby (to me), but it is definatly a learning curve and I have far more questions with e-power than I ever did with glow.

John

rahtware
08-18-2005, 09:51 AM
Please don’t get me wrong; I’m posting this out of ignorance, not to irritate.

I have read all of this before and it still leaves me with a simple “Why”. Why can’t different motors be compared side by side?

My suggestion is simple. List all of the information needed by a program like MotorCalc so a consumer can make a rational choice. Have you ever tried to wade through the entire pile of BS listed for motors to try to find “Motor Constant, No-load Current and Resistance”?

I still can’t find this information for the Multiplex brushless motors. I sent an E-mail requesting it, but never received a reply… Why? :D

stanger89
08-18-2005, 12:28 PM
I have read all of this before and it still leaves me with a simple “Why”. Why can’t different motors be compared side by side?

For the simple reason that any motor can "theoretically" put out an infinite amount of power. You could run a Speed 400, on a 4s lipo setup spinning a 12-inch prop and putting out 500-600W of power. It would probably do that, but only for a second before the real world kicked in and it melted. Basically, they can be compared side-by-side, but that comparison can't be simplified to a single number like glow engines.

My suggestion is simple. List all of the information needed by a program like MotorCalc so a consumer can make a rational choice. Have you ever tried to wade through the entire pile of BS listed for motors to try to find “Motor Constant, No-load Current and Resistance”?

Most companies do list all the info needed for MotoCalc, that's exactly what the "pile of BS" is. Motor constant, No-load current, and restistance are what MotoCalc uses to figure performance of the motor.

rahtware
08-20-2005, 08:24 PM
Most companies do list all the info needed for MotoCalc, that's exactly what the "pile of BS" is. Motor constant, No-load current, and restistance are what MotoCalc uses to figure performance of the motor.

You must have "speed read" the last of my post as I stated the three factors that are needed by MC. And going beyond this, I admit my ignorance when it comes to this subject, but I don't think I have found one company that lists those "exact" factors... As in my statement about Multiplex.

If you can help me wade through "the pile of BS" I would be most grateful.