http://www.rctimer.com/index.php?gOo...st.dwt&gcat=40

This page is of the brushless outrunners available from someone out there selling what looks like some pretty nice, high quality electric outrunner motorsl at what looks like very reasonable prices. But, the only numbers I see that I understand right of is he KV rating... and there is more to a motor than the KV rating that one needs to know to intelligently choose a motor for their plane.

The reason I bring this up is because, right now, I am that beginner, trying to make sense of selecting a combination of motor, ESC, and the battery.

I keep asking the same question both here in the Beginners forum as well as in the general Electric forum, this time in the form of a statement rather than a question: a reasonable chart that someone can use to directly choose an electric motor that has some information that we are used to in the Glow world.

For instance, we all know what a .46 two stroke can be used on. However, with the numbers presented to us for electric motors, well, it gets more and more confusing each time I look at these numbers. It just isn't easy to make the proper choice.

Yeah, I know, plane weight, wing loading, overall weight, flying style, and so on.. all factor in. But, well, so far, there just isn't an easy way to select the components when building a model.

I have five motors that all look alike, yet they are very different in what they produce and what planes they will work properly with, yet an OS .46 will work on several airframes that I have, and work just fine.

Isn't there an easier way?


CGr.

CGRetired,

That's a great topic, I wanna buy me some electric planes down the road, and these things throw me off, thatswhy I have never tried to dig it out and find out what exactly are they, but with this topic I would be able to learn something new[8D]

Good Job CG

Hi CGr,

I don't know if this helps but I have found it very useful in trying to arrive at motor/prop combos.

http://adamone.rchomepage.com/calc_motor.htm

Cheers,

Colin

Some places they are marked for you. [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXLWV6&P=0] .46 size[/link] They are nice enough to show you this [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&P=8&I=LXRDH3]ESC[/link] in the required accessories. I use this as a reference when shopping elsewhere with Kv rating only. It keeps me in the ballpark.

I hear watts is a good indicator also, 100 watts per pound is a good sport power weight ratio. Ialso read the reviews in Hobbyking to see what other people have been using on them. Took me forever to figure just the right motor for my Herr Rally XP but Ithink it turned out OK.

Colin, that's great, but consider a beginner trying to make some sense of all that. I am an engineer and some of it really taxes my pea-brain There has to be an easier way.

Phoenix... yeah, I've seen that too, which, to me, is very helpful when trying to see what will work with a certain type of plane. Unfortunately, a lot of us fly planes that weigh in at 5 + pounds. Try to figure out what the equivalent electric power for that would be, if that was what one was looking to do.

Most of the electric power is useful for lighter aircraft. Consider a recent topic about the Goldberg Progege. Yeah, it's out of production, but supposed a person had one that he/she wanted to convert to electric. There are several factors that come into play here, and all are very expensive propositions. But, aside from that, what would a person need to do to fly this plane that has a range for glow from an OS .55 to an OS .75.. that is quite a range of power options. What electric conversion would work for that?

It takes quite a bit of calculation to get it right, and if a mistake is made, then what?

Jeffe.. yes, watts per pound for flying style is a great place to start. But, that's not the point here. What is the point is trying to make sense of what is offered to us for options.. there are way to many options with electric power... there is no real consolidation of what is available. If you know a manufacturere, for instance, and stick with them, you are ok. But there is no comparision between manufacturers. With glow, for instance, a .46 two stroke from just about anybody, is pretty much a .46 glow two stroke and you can go wiht that with anything that recommends a .46 two stroke glow engine!!! Not so with electric.. as far as I can see, anyway.

As I said, there should be some easier way to do this.

CGr.

Idont disagree. It was 100 times more difficult to pick my electric motor than any glow engine .

I understand. I wasn't debating the issue... and I agree that watts per pound is a great starting place.. but once there, then where do you go unless you have quite a bit of knowledge on motor selection.

The reason I brought this up was because of engine choices for the plane I've started a build thread on.. selecting the power for that plane has come up with several options. Some will work and some will work much better... and then again, some will clearly not work. But for a beginner, where is that fuzzy line drawn and how does a beginner make the right choice?

Consider some of the RTF's out there that come with minimal power or brushed motors that clearly fly the plane, but that's about all they do. If one wants to convert that from brushed to brushless, well, how does that person do that?

That does not even cover what if someone wants to convert from glow to electric!!!

CGr.

Very good topic! I wish manufacturers would sell packages that include the motor, esc, wiring, charger, and a few battery options. I'm a retired electrical engineer and can't imagine the confusion that would exist for people not in the trade. Some of the Local Hobby Shops do a great job of taking care of the customer, but if you are doing it on your own, it can indeed be confusing. Any websites out there that sell packages?

You are so right. Consider the link that Colin provided. I understand just about everything in that calculator, but, like you, I am an engineer. Not everyone in this hobby has that knowledge and would probably not choose to use a tool like that. And, that probably fits the description of 90% of the RC'ers out there that are trying to make sense of all of this.

CGr.

They should always state the amps the motor pulls and the voltages it needs. Then you know the watt rating of that motor. Which is how powerful it is supposed to be by design.

The KV only really suggests the application or whether it's going to be a small prop, high velocity power plant (that might need a gearbox) or the other kind.

I'd say that more often than not, they do provide the amp ratings. And almost all give the voltages to provide. So very often you have a quick way to work out the power, which is what watts is.

My guess is the reason so many model motor advertisements and spec sheets are so worthless is the source. They really haven't a clue what we need to know, and simply don't care to look into our hobby to figure out what would provide better service, because they've not had to. Until one of them pulls it all together and starts cornering the market, they'll just keep on keepin' on.

Hi CGr et al,

Wow this certainly opened a can of worms, or should that be nasty dangerous electrons? Here is a Power Table developed by someone far more clever than I. I've also included an advertisement for a brand of motor that does attempt to provide a comparison to IC.

Cheers,

Colin

Colin... I like the glow to electric comparison table. Good info there.

Getting an electric plane in the air requires some system design and that is why it gets complicated. With any system, the components (in our case motor, speed controller, ESC, wiring, battery, etc.) have to interface properly with the rest of the system components over a wide range of operation and requirements. No manufacturer out there has yet solved the system design problem and leaves it up to the buyer. LHS sellers and flyers get the knowledge with practical experience so then they can help others. I see a few companies and even Tower Hobbies offering limited packages but no complete solutions yet.

I'm with CG, there really needs to be an easier way, and being serious, why can't thay just include in the motor's specs, what size/weight of a plane the motor is intended for? it's just too confusing for me

To further muddy the waters, the amp/watt load is dependent on the size of the prop, battery pack voltage and the ESC. You can have a 600 watt motor, and only get 250 watts out of it with a smaller prop and battery combination.

One of the ways I determine the size/power of a motor, in comparison to a glow engine, is to use the scorpion comparison chart. I look at the E-Flite motors which have a glow conversion number in the name. Power 15 power 25 power 32 and so on. There is also a really cool calculator that scorpion has for their motors, the link is below. It lets you pick your voltage and a prop, and it'll give you all the specifications like static thrust, pitch speed, amperage, temperature along with many other useful facts.

This is a motor comparison chart-
http://www.innov8tivedesigns.com/Sco...ison%20Web.htm

Same motor comparison chart in a pdf file-
http://www.scorpionsystem.com/files/...rison%2001.pdf

Below is a link for a zip file that had the motor calculator I was speaking of. (very cool)
http://www.scorpionsystem.com/files/..._Calc_v341.zip

Below is a sample picture of the calculator program using a 3020-890 motor with a 4 cell lipo and a APC 12x6 prop.

If you look at the picture, you can see that this combo makes 108 oz of thrust at 57 mph. The amp load is 50.3. I love this calculator!

Right.... if you're *converting* a design you have to consider the balance because usually the electric motor is lighter weight than a comparable glow engine so you've got to shift stuff around to get it to balance. I'm like Jeffie, I kinda read the reviews of what type of planes someone else is using a particular motor on to kinda get a starting point. <br type="_moz" />

Isee Super Tigre has some good motor options. 370,400,.10. The first two relate to brushed motor size replacement and the third is glow size.

However.......

Just as modelers who fly 4cycle engines would be well advised to purchase and learn to use tachometers,
modelers who fly electric would benefit tremendously from using an amp meter or watt meter for checking the performance of their power system (prop, motor, esc, and battery).

Just recently, a couple of us helped out with the maiden of a new plane. One check was to plug a wattmeter into the sucker and do some runs with a handful of props. All of them were the same diameter and pitch as it turned out. Also as it turned out, one of the props was rejected for overloading the system and one was rejected for not even loading the system worth spit. Could any one of us "hear" those rejects rpms and thrust? Nope

We wound up selecting the first prop to use for the flight tests from it's matchup to the factory specs that came with the motor. The testing of that handful of props took very little time. Removing a prop and placing the next one on takes how long? Running them up takes seconds. Writing down the numbers takes longer than the couple of seconds each runup takes.

Of course there were 3 of us doing the testing, so it took longer. (Ever hear the old saw, "If one programmer takes one day to code the program, it will take 3 programmers 3 days to code the program." That how lots of things work in real life.)

What we got out of that was one guy being amazed that a handful "of the same props" performed so differently and another guy who now does that test on every new plane in his vast collection, and who is also going back to test his "old" ones.

Beginners would probably learn a bunch from doing the same testing just once. Get more than one prop to use and borrow a watt meter if needbe. It's amazing what one can learn from doing and how little you get from just asking "what's the best prop for that motor." Which seems to be what everyone does. I guess they don't want to spend the money to buy more than one prop.

I'm a 1/2A flyer, mostly, Norvel .06 engines. They do 19,000 RPM on a 6 x 3 prop. My ThrustHP calculator says that this delivers .127 HP and converting that to Watts gives us, 94 Watts,,, just as the power table says. Neat.

My problem now is that I have a foamy Spitfire that spins an 11 x 6 , SCALE, three blade prop. I wanted to convert that to a diesel engine to get the roar of an engine into the illusion. No go, no way that a small diesel will spin that size of prop. So electrics are a WHOLE new ball game to me.

And that Spit, on an electric motor, with that prop, flys very realistically. Will they ever come out with a device that could blast out the roar of a Merlin, 12 cylinder ?

scooterinvegas brings up a good point. With glow, if you change props, you change RPM and how the aircraft may perform in the air. If you do it with electrics, you get both, but you also get one more factor that can definitely break things. If you overcurrent a motor and ESC, you may not have time to prevent damage.

Da Rock also makes an excellent point about the tach and the watt meter and their use. Both are necessary... however, with glow engines it may be ok to "tune by ear". Try that with an electric motor!! In that case, you may be using your eyes to watch the smoke rise from the ESC or the windings of the motor.

CGr.

Well, let's see Dick... You can get an OS 46AX, or an OS 46LA, or a Thunder Tiger TT46 Pro.

All 46-size engines, all different.

I DO see your point though, I just don't think it's as simple as a single number rating.

It's like we tell beginners all the time - Get the biggest engine allowable so you can use it on bigger things later and for now, throttle back

Yep, Mike, I understand the differences in the engines, but it just ain't that easy with electric. But, I am a big subscriber to the bigger the better with glow. Unfortunately, with electric, usually bigger means more weight and more current draw... and the problem grows exponentially...

But, yeah, I do wish there was a simple number system that one can say for this plane, get this number motor/esc/battery combination and off you go. The trash that comes with the RTF's is almost useless so if a guy wants to get more out of his model, well, the pit opens up and woops.. we fall right into it.

Dick.

Keep in mind that current draw is directly proportional to power used.

ust like in a glow engine, if you have a 46 that you fly at half throttle, your fuel will last longer that if you flew it at full throttle.

Likewise, if you fly an electric at half throttle, the batteries will last a lot longer.

This is very true. But, the problem that comes up is that if a plane is underpowered, and you go to full throttle, well, there is a good chance that the smoke maker starts to work and all that canned up smoke comes out of something. With glow, well, all you get is... well, at times, nothing but a model that rolls around on the ground but never makes it up in the air.

I like to "over power" even my electrics for that very reason. Bigger battery packs with more capacity to get more flight time. But, again, weight is a bigger factor with electrics than it is with glow... to a point.

Boy, I say "even my electrics" as though I was a pro with them... ha.. not so, for sure. I fly them, but am a totally a glow person.

Dick.

When I got back into r/c flying, after several years hiatus, I got back into it with electric power. All there was available at that time (late 90's ) was brushed motors and NiCds... (and not much at that )
NiMh cells were yet to come on the scene...

Now...there is SO MUCH available, it literally staggars the imagination! [8D]

It's hard, even for someone who's experienced, to keep up with all the new stuff that seems to be introduced every month...