digital_trucker

Okay, here's the deal; I'm sure this subject has been covered ad nauseum, but the more research I do the more confused I get. I've been a 1/2A pilot for a long time, but frankly I'm getting disgusted with dealing with the continual lousy design of them (nobody makes a truly modern 1/2A engine, and nobody seems to be willing to pay what such an engine would be worth). I know how to design an airframe sized to take a .049 glow engine, and now I'm wanting to go into electric. The subject is extremely confusing, so I need some hand-holding. From reading, I've determined I need to have around 100-125 watts, and I want to use a propeller no larger than 7 inches (this should keep things with the 1/2A range, right?). I've also determined that brushless is the way to go, and probably LiPo batteries for weight considerations.

Now, here is my question, and the bit that has me confused (and considering giving up on the whole mess). Surely there is a general, ballpark motor/battery combination that will work as a drop in replacement for a 1/2A engine...and suitable for everyday sport flying? I can't find my wizarding hat to make heads or tails of all this mystical, esoteric discussion.

Walt Thyng

My Feedback: (9)

couple of thoughts. Go to common Sense R/C, Radical R/c or New Creations R/C and take their advice. If you contact NCRC be sure to ask for Kirk. Once you have a working system then you can worry about learning the complicated stuff - and it can be done! I'm a self-taught e-flyer. Learned e-power (not r/c flying) by reading everything I could find. One of the best sources was [email protected]. The Ampeer archives are filled with all kinds of easy to understand info aswell as some pretty esoteric stuff. come to think of it Ken Myers is very helpful.
Walt

digital_trucker

Common Sense R/C is EXACTLY what I was lloking for (and it is common sense, too). You know what your plane will weigh, you know what kind of flight performance you want, figure them together and here is the combo you need. Nice and simple, and no eye of newt required.

digital_trucker

So, if I plug in the motor, battery, and prop I want to use into motocalc and it doesn't yell at me or spit out an error message I should be good to go, right?

Here's what I have; a scratch-built Jr. Falcon. Guesstimate of weight sans motor, ESC, and battery is probably going to be around 15-16 oz. It's going to be 4-channel, with one servo for each aileron (Hitec HS-65 servos, and a Spektrum DX-6 Rx).

The power combo I've come up with is as follows (via Tower):

Great Planes Rimfire 28-26-1600 Out-Runner Brushless
Great Planes Silver Series 25A Brushless ESC 5V/2A BEC
Great Planes ElectriFly LiPo 11.1V 1250mAh 15C BP Srs

The above swinging a 7x4 prop, and I assume the battery will also be powering the Rx. Does this setup look all right? Motocalc doesn't yell at me when I plug this stuff into it (although it says the prop should be a 7x3.5..maybe I could trim a little off the blades?) I also used what seemed to be the GP equivalent of waht Common Sense R/C recommended.

Time Pilot

Here is Tower's page:

http://www3.towerhobbies.com/cgi-bin...?&I=LXLWT4&P=7

Does it makes sense to everyone here that a 41g motor can put out 190 watts constant?

Even an Axi of the same weight isn't rated max that high:

http://www3.towerhobbies.com/cgi-bin...?&I=LXPPV4&P=7
(this Axi higher KV, but for comparison...)

Matt Kirsch

My Feedback: (21)

190 Watts surge. Only for a few seconds at a time. The AXi will do the same, but they don't advertise it because it's not really practical.

That looks like it should make a nice 1/2A conversion setup, IMHO.

fireman7875

My Feedback: (7)

I will have to admit that I am in about the same boat as DT. I am new to electrics too and still trying to learn how all the specs and ratings fit into overall performance. In his case, with the Jr Falcon, would he be better off with a direct drive inrunner instead of an outrunner since he wants to turn such a small prop at higher rpm? For what reasons would you use one instead of the other?

I certainly don't want to thwart your progress, DT; I am really asking more for my own knowledge but that may give you something else to consider. I, too, have been a long time 1/2a flyer recently converting to electric. I also have a Jr Falcon that I absolutely love! [8D]

Brian

digital_trucker

I know what all the electronic Merlins in their star-spangled wizard hats will say; but it seems to me that if you're used to an engine (of any size) then you know what size prop and what RPM that engine generally swings....and you also know what airframe that engine can fly. It therefore makes good old-fashioned common sense that a lekky setup that can swing the same size prop at the same RPM will fly the same airframe (if the weight of the motor/ESC/battery is roughly equal to the engine/full fuel tank/radio battery). Granted, this very well may NOT be the most efficient setup, but it would provide a frame of reference...and would help to eliminate a lot of confusion. It don't matter what size the engine is, it's the propeller that moves the plane...(can't see how an electric setup can work any differently).

Therefore, it would seem that any setup that can turn a 6x3 prop at 19K is the equivalent of a 1/2A engine...all that's left is to worry about weight. It's easy to figure out what kind of thrust. Now, working with static thrust figures (yes, I know actually flying it makes static thrust calculations basically wrong - but it suffices for our purposes)...a 6x3 prop turning at 19K will give you roughly 19 ounces of static thrust (depending on the make). Given this knowledge, it should be a very simple matter for the folks who really KNOW the hardware to be able to pick out a motor that can swing that size prop at that speed, then pick the ESC and battery that can deliver the juice necessary to satisfy the motor.

Instead, we have to brush up on our calculus and discuss all sorts of ethereal weirdness and get totally confused...it's just plain silly to insist that a non-informed person HAVE to go through hoops to figure out what they need. You know the weight of the airframe, you know how it's supposed to fly (or if you're used to engines, you know what siez engine equivalent you want). There's really no need to have to be able to discuss the hobby equivalent of particle physics just to answer the question of "what combo will fly a 1/2A plane?". The answer should literally be THIS direct-drive package or THAT gear-drive package.

If you go to buy the right engine for a plane you don't have to get into a discussion on metallurgy and chemistry, you just need to know the what size engine will generally fly a plane, and what size prop that engine likes, and what kind of fuel it runs best on. There's absolutely NO reason why picking out an electrical combo that will do the job should be any more difficult. Leave the minutia to the folks who want to wring the ultimate out of the hobby...shouldn't be necessary for the average sport-flyer or the newcomer.


Now, having said that, let me go and prepare to man the battlements and heat up the boiling oil to resist all the lekky geeks who will want to tar and feather me....and thank goodness for Common Sense R/C!

Time Pilot

No, Matt. On Tower's website, they say 190 watts constant:

"Max. Constant Current: 17A
Max. Surge Current: 25A
Max. Constant Watts: 190W"

I don't believe it, but there it is. Just make sure you get the extended warantee if you're going to drive it to those specs.

dashunde

It wouldn't surprise me at all if that Rimfire can handle 190watts constant.

I think it will be just fine on a 20-30oz park sport-type park flyer.
Trucker, it looks like a good combo there.
I do think you would be better off with a 20-25c 1350mha 3cell pack though.. try these...
http://2dogrc.com/ecommerce/os/catal...nt-p-2178.html
I have a few for my 200watt Airfoilz Yak and like them a lot.
They will stand up nicely to your 190watt system without getting hot and you'll get good punch and run times.

Trucker... Here's the thing... Electric props are very different from glow props, and you need to use a electric prop so that it remains efficient.
Doing just the voltage and Kv math will not yield accurate rpms either - the Kv rating is a no-load number.
Either way, your on the right track with that Rimfire... small prop, high Kv motor will emulate a little nitro pretty well.

I know getting into electrics is daunting... just keep reading and fooling around with it. It will all come to you.
You'll also find that there is a big expense hump to get past, but once you have lipo's and a couple of chargers it gets much cheaper and easier. Start off with good packs and a quality charger.
I really like the Cellpro 4s lipo charger/balancer from fmadirect.com... absolutely excellent little charger.
http://www.fmadirect.com/Detail.htm?...218&section=45
Dont forget to grab this adapter...
http://www.fmadirect.com/Detail.htm?...271&section=45

digital_trucker

I did order the Cellpro 4S charger and adapter doodad. I'm not terribly happy with the rimfire though (it's not really set up to do anything but use the prop-saver). I picked up the equivalent Common Sense R/C motor and I like that much better - it has absolutely everything needed whether I want to use a prop saver or a NORMAL spinner/prop combo.

fireman7875

My Feedback: (7)

DT, just turn that Rimfire around and put a prop adapter on the bare shaft and voila you have a regular shaft like you are used to. I don't care for the prop savers either. Generally, there are two choices available in prop adapters: the set screw type and the collet type. Personally, I hate the collet type because the aluminum they are made of is fairly easy to wear. So if you crank down on the prop nut a little too hard and then try to take the prop off sometimes it will spin on the motor shaft and you'll ruin the adapter. I much prefer the set screw type. It seems more secure to me.

Brian

Dr Kiwi

It wouldn't surprise me at all if that Rimfire can handle 190watts constant.

It would surely surprise me... I tested a bunch of Rimfires for GreatPlanes and every one of them got hot long before the rated amp/watt limit.. IMHO they are all very optimistically (over-)rated!

ss40

I have converted a Norvel Ucan2 that was supposed to be .049-.074 (1/2A, 40 inch wingspan, 24 oz.)and used a GWS 2208/18T ($20) and CSRC 1250 3 cell packs($25). Also a Thunderpower 3 cell 1320 pack. I use a 25amp ESC(overkill.) This thing really flies well and has a lot of flights on it and the motor just keeps going and going. 9x5 prop. Isn't .049 about speed 400?? size.
I also use this combo on a Tiger 400 ARF (not TigerMoth....Tiger). I love the size and performance of these models.

I also had a Phoenix ARF from Hobby Lobby which was a little heavier and a little less nimble with the combo but Hitec HS-81's let me down for the first time and it is kindling.[]

http://www.allerc.com/product_info.php?products_id=2341

dashunde

Bummer...
I have a little 22m-1000 that I cant seem to kill.
Its been a great little motor (got it used) and it has hundreds of flights on it.