fiveinarow

It seems to me there's a LOT to learn about electric flight. As a veteran R/C'er I was comfortable in my nitro and castor oil world, but I'm pretty well lost in this new world of electrons!

SURELY somebody has written "the book" that explains all of this in one handy reference. (If NOT- one of you veterans needs to get busy at the computer and write it!)

From LiPo and LiMg to watts and amps I'm confused. I mean, I can see what various websites have assembled for any given plane, but I really would like to know WHY they chose a 3s pack instead of a 2s pack- why a 900Kv (whatever Kv is?) motor instead of a 1250Kv motor, why 1200 watts is enough to take a specific plane vertical but 1000 watts isn't, etc., etc., etc.

I've downloaded MotorCalc and I can see that every detail interacts with every other detail to determine final performance- but again, I don't understand WHY it all interacts the way it does.

So... IS THERE A BOOK... or a web-based series of tutorials that takes a guy who doesn't know an electron from a proton and gets him to the place he can understand what's going to happen if he uses a 12 turn motor instead of a 10 turn motor or adds a 4th cell to a LiPo pack???

Thanks for any suggestions,

Steve - the Electro-Moron

dignlivn

Steve

You are not Alone . I haven't found the book, but there are
chapters (threads) here at rcu.


Bob

mvarzoni

Well dude, we are all at same boat!

I'm totaly lost!
I just wanna set up a zagy, but I simply can't find info's about ...


Mauricio

patnchris

That's why you have this wonderful place where you can ask questions and draw from the knowlege of the guys that have been there and done that...........Pat

jdetray

Not as far as I know. Each of us can probably provide a small piece of the puzzle. My contribution:

One starting point for determining what sort of power system you might need is "Watts per Pound." Here are two versions that I've seen.

Version 1
[ul][*]< 50 watts per pound Unable to rise off ground [*]50 to 60 watts per pound Can rise off ground and perform simple aerobatics [*]60-75 watts per pound Easily loops from level flight. More impressive aerobatic performance. [*]75-100 watts per pound "Fighter"-like performance. Aggressive climbs [*]100-150 watts per pound Extended vertical runs. Unlimited aerobatics [*]> 150 watts per pound Wings are unnecessary
[/ul]

Version 2
[ul][*]50–70 watts per pound: Minimum level of power for decent performance, good for lightly loaded slow flyer and park flyer models[*]70–90 watts per pound: Trainer and slow flying scale models[*]90–110 watts per pound: Sport aerobatic and fast flying scale models[*]110–130 watts per pound: Advanced aerobatic and high speed models[*]130–150 watts per pound; Lightly loaded 3D models and ducted fans[*]150–200+ watts per pound: Unlimited performance aerobatic and 3D models
[/ul]

So if you have a plane intended for a particular type of flying and you know its weight, you can use the above as a rule of thumb for estimating the required power in Watts.

kV is motor constant which tells you a motor's RPM/volt. A motor with a kV of 900 will spin at 900 RPM per volt. At 5V, this motor will spin at 900x5 = 4500 RPM. At 10V it will spin at 900x10 = 9000 RPM. These are no load numbers (without a prop).

In practical terms, the higher the kV, the greater the RPM, but the less the torque. So ...

A low kV motor is best suited for spinning a large prop at relatively low RPM with high troque, suitable for a slow flyer or a 3D plane where thrust is more important than speed.

A high kV motor is best suited for spinning a small prop at high RPM with low torque, suitable for a fast-flying plane where speed is more important than thrust. At the extreme end, ducted fan systems use extremely high kV motors.

To complicate matters, a high kV motor can also be used with a gearbox to give it more torque, allowing it to turn a large prop. In the case of helicopters, a relatively high kV motor is used with gearing to turn the rotor.

For a given motor design, fewer turns increases the kV while more turns decreases the kV. Unfortunately, comparisons of the number of turns are valid only for motors of the same design, so one manufacturer's 10-turn motor may be very different from another manufacturer's 10-turn motor.

Some vendors have posted guidelines for converting glow power to the equivalent electric power . Here's one of them.
http://www.horizonhobby.com/Explore/...ArticleID=1563

Otherwise, ask specific questions to get specific answers!

- Jeff

fiveinarow

jdetray...

That's at least a good downpayment on a book!! Thank you!! And thanks to others who have posted as well.

I just sat down and studied several data sheets on motors and a few lightbulbs turned on with the information you shared.

I'm going to study this some more in the morning, but I think you just answered about 70% of the basic questions with one post!!

Thanks again,

Steve

fiveinarow

jdetray...

More study this morning continues to bring more understanding as I study various batteries, motors specs, etc. It's beginning to make sense thanks to you!

I do have a follow-up question. I'm pondering similaries/differences in motors.

Here's an example:

Hyperion HP-Z3025-08 vs HP-Z3013-16

Both have 30mm stators but one has a 25mm long stator with 8 turns, the other a 13mm long stator with 16 turns.

Both produce exactly the same Kv @ 985

There are slight differences in efficiency and resistance. Both are suited for for 2-4 LiPo cells

Obviously- they are different physical lengths but same external diameter. The smaller 13mm stator model is about 1/3 less weight. (110 vs 185 grams)

But HERE is a significant difference in the two: The 3013-16 has peak current of 37A while the 3025-08 has peak current of 52A

There are obvious implications for how many watts each motor can produce, even though they're the same diameter and produce the same KV?!?


This difference APPEARS to be some sort of "universal rule" that of two otherwise identical motors, the one with LESS WINDS can always handle MORE CURRENT? So it appears that on otherwise identical motors...

Less winds produces MORE KPV and can handle MORE AMPS
more winds produces LESS KPV and can handle LESS AMPS

Is that always true?

And further... if less winds can handle more amps then it would SEEM that lower wind motors (of the same design) will produce more watts given the same amount of voltage applied since watts = volts X amps. Or have I missed something obvious here?!?

And in another related area, are there any universal differences between otherwise identical motors with different stator lengths other than one is simply "longer" than the other?

If this is a stupid question- I apologize. The answer may be: It is what it is! LOL!

Thanks for any additional insights,

Steve

jdetray

Hi Steve -

For a motor of the same design, if you double the length of the stator and halve the number of turns, you should end up with a motor of the same kV. And that's what you see with the two Hyperion motors.

Regarding the current, it's not that the motor with fewer turns can handle more current, but that it will draw more current. Ohm's law tells us that I = E/R. That is, current equals voltage divided by resistance. Fewer turns of wire has less resistance than more turns. In addition, with fewer turns to fit on the stator, you can use larger gauge wire, which has less resistance than smaller wire. So with fewer turns and larger wire, resistance goes down, and current goes up.

The end result is that the larger motor draws more current, which equals more power (Watts). Depending on your intentions and the prop you choose, more power can make a fast plane go faster, or give you more thrust for better 3D performance, or let you fly a larger plane. It all depends on what you want to do with the additional power. Of course, in order to get all that power from the larger motor you will need a larger battery in order to provide all the current the larger motor needs. (This is why lipo batteries have revolutionized e-flight. For the same current capacity, lipos weigh about a third as much as NiCd or NIMH batteries. This big increase in power density has allowed e-flight to flourish.)

Now if we leave the stator size the same and just put fewer turns on a motor, the kV and the current will go up. Since motors are never 100% efficient, some of the additional power will be converted to heat. If we put few enough turns on a motor, the waste heat can be enough to start overheating things. The insulation on the windings can melt, or the magnets can overheat to the point where they are permanently damaged. For this reason, a motor with few turns is often called a "hot wind."

Many a motor has been fried because the pilot put too large a prop on a motor with too few turns. The motor draws too much current and overheats. So don't think of low turn motors as "better" than those with more turns. It all depends on how the motor will be used -- everything in e-flight is a trade-off. Excessive current can also damage a battery. In a poorly designed power system, it's often a toss up as to which component will fail -- the motor or the battery.

- Jeff

fiveinarow

Jeff,

Thank you again! MORE good information to chew on and plug into MotoCalc and study.

I hereby nominate YOU to write the E-Book. And frankly, I suspect there's a huge audience for it. Make it a downloadable e-book for a few $ and never even touch it. Just help people out and put a few $ in your PayPal account to support your hobbies!

Again... thanks. If I have another question I'll be back.

Steve

jdetray

Hi Steve -

There are plenty of people who I would nominate to write "The Book" who know a lot more about the topic than I do. My knowledge comes mostly from the fact that I have built a few of my own brushless motors, so I have a good practical grasp of a few things.

Theory is one thing, but where it gets difficult is when you are trying to figure out which motor, prop, ESC, and battery you need for a specific plane. If you only ever fly planes with the manufacturer's recommended power system, it's pretty easy. As soon as you depart from the recommendations, the best course is to find someone who has already done it and ask them what works and what doesn't.

That's where these online forums can really help. Chances are good that someone has already done it. And if not, there are people who can make good recommendations if you post the type of plane, its size, weight, type of flying, etc.

- Jeff

fiveinarow

Jeff,

Made your own brushless motors?!?! YIKES!

But then again... I went to your astro site, read your bio (I've read several of the magazines you've been involved with over the years) and followed the links to your (son's? brother's?) airplane site, etc.

Bottom line: I know a braniac when I meet one! LOL!

I'm impressed with the BREADTH of your accomplishment, and you've got more than enough knowledge to help my feeble gray brain get up to speed on this brushless e-flite thing.

Thanks again,

Steve

jdetray

That's my brother's web site, [link=http://www.modelaero.com]ModelAero.com[/link]. One of his early prototypes was tested with one of my home-built brushless motors, similar to the one below.

- Jeff

smh20502

My Feedback: (1)

try this site

http://geocities.com/aero_ebook/airplaneebookinpdf.htm

I've got the heli version and it a welth of information.

piroflip2

Join the club.
I have just ordered an Angel S Evo 50 for short F3A practice sessions and although I have been flying for over 30 years it is all new to me. Electric is the future and after the recent drop in lipo prices in taxed to the hilt Britain I thought I would give it a go.

No mess, no YS shaking the airframe to bits and no starting/idle problems here I come .

aeajr

My Feedback: (2)

Here is an e-book on Electric flight. This should address a lot of your questions, and it is FREE.

EVERYTHING YOU WANTED TO KNOW ABOUT ELECTRIC FLIGHT
http://www.rcuniverse.com/forum/m_7100376/tm.htm

You can post questions there or here.


If you prefer paper books, there are lots of books on e-flight. They are great for general information but any product specific information will likely be out of date. Your local hobby store should have some books on e-flight.

Here are a few available on Amazon:
http://www.amazon.com/How-Build-Elec...3446746&sr=1-1


http://www.amazon.com/Control-Airpla...3446746&sr=1-4