ABC's of electric motors?

[Fly Time]

Does anyone know of a good place on the web to get good basic information about electric motors and batteries? I am just getting back into RC flying after 15 years and am a bit overwhelmed by all the new terms. What is inrunner vs. outrunner? 2 cell vs 3 cell? 400 speed vs. 480 speed? What is KV value? Max amps vs. burst amps? What do I look for in model numbers or specs to know what motors are equivalents between brands?
??

[yossarian]

I feel your pain Payne. (sorry, couldn't resist)
I'll try to give you some basics and try to google up a good site.

In-runner means the stator is spinning inside of the 'motor shell' or often referred to as the 'can'. For a brushed motor, it has actual brushes that run against the commutator to complete the electrical current. This is very ineffecient as the brushes create friction against the stator and the brushes also wear out overtime.

Enter Brushless motors. They do not need brushes to make physical connection to the stator, this is why they have three motor leads, instead of two. One negative, one postive, and one 'super secret squirrel mystery lead'(well now you know :p). They rely on signals from an Electronic Speed Control(ESC) specially made for brushless motors. It basically fires the magnets in sequence causing the motor to spin. Much more effecient, the motors lifespan increased greatly, longer flight times, and faster speeds.

Outrunner means they've moved the magnets and placed them on the inside of the can itself, that's why the entire thing spins. Why would you do this?? It allows for higher torque at lower amps, which means you can spin a larger prop.

2 cell vs 3 cell. Consider your TV remote control. It has probably at least 2 aa batteries. If I were to wrap those two aa batteries together, I would then have a 2 cell battery pack. The cells can be any size. They can also be any flavor. You can have a 2 cell Lithium-polymer( Li-po) pack as well as a 2 cell Nickel-metal hydride pack. What is more important is the Mah rating, or milliamps per hour. This is like the size of the tank. A 3 cell 1700 Mah pack will run out of juice faster than a 3 cell 2100mah pack if they or run on the same amp draw over time. The 'C' rating is it's 'continous discharge' rating. This is like the carburator or fuel injector. It's how fast the battery can empty it's tank. A standard 3cell 2100mah lipo pack might have something like 30 amp(continous discharge) with 45 amp burst, meaning for usually about 10-15 seconds it can dish out extra amps. Think of it as after burner. ;) Amps = Watts x Volts.

Kv is a rating given to motors based on how many RPM's per volt. A 2700 kv motor is faster than a 2100kv motor. An example is my 2700kv brushless motor can push my stryker(AUW 26oz) about 100mph. Where as I use a 1500kv brushless outrunner on my ling cat, which could easily handle more motor, but I want plenty of quick thrust under my thumbs as I'm getting aquainted with this style of plane. Later I'll likely go to an inrunner with a higher Kv rating for more flat out speed.

Not sure on what 400 speed vs 480 speed means. I think it's just a way to rate brushed motors. Like the 'stryker b' comes with a 480 speed brushed motor, which is adequate to get you going, but not as fun as a brushless motor.

To be honest, the way I get planes into the air is consult Wattflyer. Whatever plane I'm building, there's almost always people who have done it and can suggest all manner of power train options. LHS's can sometimes be good places to get ideas, in fact, you're close to Todd's Models in North bend. You can just tell that guy what kit you have, tell him what you want it capable of, and he'll spell out exactly what you need. More of a UPS drop than a store, but he knows electrics.

Just realised you are in Renton. I grew up in Federal Way but in Yakima for now. Howdy neighbor!

Welcome to Wattflyer too.

Dave

[yossarian]

Oopps, here's a good site.

http://www.gobrushless.com/kb/index.php?title=Brushless_101_-_Chapter_1

[Fly Time]

Thanks Dave! Very good explanations. I will also read through the web link when I have a little spare time today. From the title it looks like exactly what I was hoping to find. What a great resource WF is!

[jasmine2501]

Note: the three wires on a brushless are not negative, positive, and something else. They are all negative and positive at the same time. The ESC sends an alternating current into each one. Thus they are 3 "phases" rather than the standard thinking of power and ground or positive and negative.

The numbers on motors such as 400XT, or whatever, seem to be a lot like the sizes on clothes - they don't mean much, and they vary from one manufacturer to another. The KV rating is what you need to look at. More KV is going to be more powerful... here's a quote from a web site not worth linking

"RPM stands for the number of rotations per minute, and signifies how fast a motor spins. Brushless motors are given a Kv rating, which is RPM per volt, that lets you determine how fast that motor will rotate with a given voltage supplied to it. A 980Kv motor powered by an 11.1V battery would spin at 980 x 11.1 = 10878 RPM with no load. The current rating specifies the maximum continuous and/or burst current that the motor is able to handle. When selecting a battery and speed control, choose ones with continuous current ratings equal to or greater than that of the motor."

And here's some good articles from the ultimate source of Everything Worth Knowing:
http://en.wikipedia.org/wiki/Brushless_motor
http://en.wikipedia.org/wiki/Lithium_ion_polymer_battery

Oh I almost forgot... this little software can tell you everything you need to know about the numbers:
http://www.motocalc.com/

And here's an online version of the same thing:
http://brantuas.com/ezcalc/dma1.asp

[Sir Raleigh]

Here are a couple more:

http://electronics.howstuffworks.com/brushless-motor.htm
http://www.howstuffworks.com/framed.htm?parent=brushless-motor.htm&url=http://www.modelflight.com.au/brushless_motor_faq.htm

[jasmine2501]

I've been playing around with that calculator and it's pretty accurate with my observations. I put in my Stryker setup and it correctly calculated the amps, minimum flight time (6:30 min) and final maximum pitch speed (55mph) so I think you can trust that online one. There's another one here, but it has fewer selections:
http://brantuas.com/ezcalc/multiplexcalc.asp

[Fly Time]

Good stuff everybody. Thanks!

[yossarian]

Note: the three wires on a brushless are not negative, positive, and something else. They are all negative and positive at the same time. The ESC sends an alternating current into each one. Thus they are 3 "phases" rather than the standard thinking of power and ground or positive and negative.


Pfft, just when I thought I knew something about BL motors, a pretty lady comes by and dashes my ego. :(

I believe you completely, and to be honest I always thought two of the leads became designated positive and negative, otherwise how is it possible to reverse the direction of the motor by simply switching two leads??

It's INCONCEIVABLE! (For Princess Bride fans)

[ptgarcia]

Pfft, just when I thought I knew something about BL motors, a pretty lady comes by and dashes my ego. :(

I believe you completely, and to be honest I always thought two of the leads became designated positive and negative, otherwise how is it possible to reverse the direction of the motor by simply switching two leads??

It's INCONCEIVABLE! (For Princess Bride fans)


I believe it's because you change the phase by 180*, thus reversing the motor direction.

[FlyingMonkey]

It's INCONCEIVABLE! (For Princess Bride fans)

even as a man, I feel comfortable saying...
great movie!

it's an even better book.

[yossarian]

even as a man, I feel comfortable saying...
great movie!

it's an even better book.

Dave, "I'll read it, but I'm learning to cook."


Vizzini, "No more rhymes, I mean it!"


Fezzik, "Would anyone like a peanut?!"

[jasmine2501]

I believe it's because you change the phase by 180*, thus reversing the motor direction.

Sort of, but yeah... that's why you can switch them around without breaking it. And it's a little more complicated than a sine wave... it's apparently a square wave going to each lead, but it causes the magnetic field to rotate around in a circle, and that's what's important.

[FlyingMonkey]

Dave, "I'll read it, but I'm learning to cook."


Vizzini, "No more rhymes, I mean it!"


Fezzik, "Would anyone like a peanut?!"

My younger brother (who has downs syndrome) loves that quote!

He uses it to torture my girlfriend. Well, that among many other little tricks he's learned :D

[Lip84]

I was just wondering, as I am setting up a new power system for a pylon racer, what the "turns" of an inrunner mean?

I am using a Mega 16/15/5, which is a 5 turn motor, and have noticed it is not as powerful as a 4 turn motor (the 16/15/4).

Explanations?