Back in the dark ages of brushed motors, I understood what the esc did, it put out a voltage set by the incoming pulses.  Now with the brushless motors, I find I am not sure just what the output versus input is.  I thought that it sent out pulses at a rate set by the incoming signal, but if that is true, why would rpm change with battery voltage, making the governor mode necessary?

In addition, how does the kv of the motor enter into the equation?  If the pulses are sent out by the esc, how come the speed varies with different windings?

HELP?    

I will give that little larger can ... as soo as they did not went too far ...

simplest answer will be following ... if you understand classic DC motor with permanent magnet and commutator, controlled by PWM ESC (PWM controlled by incomming R/C pulses), then our BLDC motor with BLDC ESC is EXACTLY SAME THING ... there in only one small almost irrelevant difference, and that is, that commutator is closed inside the ESC instead of the motor. ... and may be another, that we rotate magnets and not winding.


So the KV is the same KV as we know from DC motors as well as IR and I0. The name "brushless" means only fact, that we replaced brushes by semiconductors ... nothing else 

Thanks, Igor, but I am still in the dark. 

Does the brushless esc read the motor rpm and drive the pulses around that? Or does it generate the pulses to control the rpm.  Does it control voltage, or the duration of the power pulse.  I am sorry, but your answer is way too vague.  Also, then, what is the difference between regular drive and governor?  What, exactly, does the output look like in varying situations?

I really want to get into the nitty-gritty of understanding this thing.

A second question arises, what makes different motors have different kv's?  I understand that there are motors with different numbers of poles, and different windings, but haven't a clue how those interact.

Thanks, Igor, but I am still in the dark.  

Does the brushless esc read the motor rpm and drive the pulses around that? Or does it generate the pulses to control the rpm.

It senses the motor position and drives pulses based on that.  Modern ESC's are "sensorless", meaning that the motor needs to be turning for them to sense the motor position, so there's a little start-up song and dance they do -- but once the prop is spinning, they're just going by the motor position.

Does it control voltage, or the duration of the power pulse.  I am sorry, but your answer is way too vague.

Well, yes and yes.  They control the average voltage that a coil sees by pulsing the power to the coil on and off.

Also, then, what is the difference between regular drive and governor?

In regular drive the duty cycle of the pulses (i.e. the on time vs. off time) is fixed by the command from the receiver or timer.  In governor mode the ESC uses the fact that it's sensing the motor position to control the speed of the motor by varying the duty cycle as needed.

What, exactly, does the output look like in varying situations?

Hash.  (Sorry -- I couldn't resist)

If you look at the drive to a motor terminal with an oscilloscope you'll see it jumping up to the battery voltage, drifting somewhere in between, and jumping down to 0V.  The amount of time it stays on one rail or another is the duty cycle, the rail that it's staying on is determined by what the ESC thinks the motor position is, and where it is when it's drifting in between depends on the motor speed and position (which is how the ESC tells where the motor is).

I really want to get into the nitty-gritty of understanding this thing.

Hoo hoo hoo ha ha ha ho ho ho -- I've been working with motors in my professional life for over 20 years, and I still don't understand everything about them!  And when I meet someone who designs the motors that I use, I find out that they know very little about making them sit up and beg the way I do!  So you can't know everything.  Have you looked at the Wikipedia entry on DC motors yet?

I started learning this stuff by making motors out of bell wire and nails.  Granted, I was 11 at the time, but I think that's still a good way to start.  You learn a lot about how motors work from dinking around with little hand-made ones.

A second question arises, what makes different motors have different kv's?  I understand that there are motors with different numbers of poles, and different windings, but haven't a clue how those interact.

Kv is really the opposite of the parameter that motor people like to use.  The 'real' parameter is the torque constant, which is a function of the physical construction of the motor and the strength of the magnets times the number of turns.  Kv is proportional to 1/(torque constant).  So if you take a motor that has 10 turns on each winding, take it all apart, find some wire that has exactly twice the area of the wire in the motor, and rewind the motor with 5 turns per winding, then several things will happen: the torque constant will go down by a factor of two (because you took out half the turns), the motor resistance will go down by a factor of four (because you decreased the length of the conductor by two, and increased its area by two), the Kv will go up by a factor of two (because it's proportional to 1/(torque constant)), the power required by the motor to generate a certain amount of torque in stall will remain exactly the same, the power required by the motor to turn the motor at a certain speed will remain exactly the same, and the efficiency will remain exactly the same.  (Well, almost exactly).

So, strengthen the magnets and the Kv will go down (and -- most likely -- efficiency will go up).  Increase the turns and the Kv will go down.  Change the number of turns while keeping the same amount of copper in there, and all the motor's power equations stay the same, only the voltages and currents change to reflect the different wire.  Increase the gap between magnet and armature and you're effectively weakening the magnets, so Kv will go up (you can regulate the speed of a separately excited field motor this way).

I'd have to sit down and think through the math (which I'm disinclined to do right now) about what happens if you add more poles.  Diameter goes up, which increases the leverage of your magnets, which increases the torque constant (and decreases Kv).  The number of poles go up, so if you connect them in series that'll make the torque constant go up (more identical poles all pulling together with the same current), which will make Kv go down -- but if you connect them in parallel the torque constant will go down (because of identical poles stealing current from one another).  Meanwhile you're redesigning the motor anyway, and if you use different magnets or make the armature deeper that's going to affect everything too.  After a while you forget how to design ESCs and you just sit around making motors -- augh!

I think that that was marvelous!  I am sure you answered all my questions, but it will take a while to incorporate all that info! I am going away and doing some serious omphalaskesis for a while to incorparate all this!

If you find any lint in there, don't get it in your motors.

  Thanks, and with luck, I won't have more questions.   

Well, if you can't dazzle them with brilliance...

Sorry, I am a wet motor guy.  What are IO and IR?

OK, litle more light ... and then read what Tim wrote ...

Kv means how many RPM motor does unloaded depending battery voltage. Means if your motor has 1000rpm/V and you use 10V battery, it will make 10 000rpm. If you use 5V battery, you will get 5000rpm. It means that the rpm depends on voltage and that the ESC does not controll RPM by its frequency. Everything is exactly like any other DC motor.

I0 means amount of current necessary for that unloaded run, and does not mean too much for understandinding how it works and I will ignore it for next text.

Ri is internal resistance of the motor. And it means, that if you LOAD the motor, to for example 1A and if that resistance is 1ohm, then the motor wil see only 9V effective, because you will loose thah 1V on that resistace (1A * 1ohm = 5V) ... means rpm of the motor will be only 9000rpm even with 10V battery.

Means if you really want to have 10 000rpm LOADED, you must choose higher voltage ... for example 11V ... but unloaded motor will go to 11000rpm and this is what we do not want, so governor is a device, which will throttle down unloaded to those 10 000 and throttle up when loaded to keep tose 10 000rpm.

clearer?