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Jun 26, 2012, 12:49 PM
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Thread OP
Help!

DIY Brushless ESC Theory


Hello everyone,

I'm new to this whole multicopters world and I need help in some aspects. First of all, I'm an student and I want to make a tri, quad or hexa (it's not decided yet) with the Multiwii software using Arduino. But I would like very much to do the ESCs myself, without buying them. I've been looking around ESCs brushless desings but I'm lost. I know there are one-phase ESCs, two-phase ESCs, and so on (which I deduct have to be depending on the number of poles). But the type depends on the motors, and I don't know what type of motors use, so I can't really start looking deeply into the desings. Which type of motor shall I use?

But there's another thing I don't get: I've seen that there are also two other divisions: sensored and sensorless. I thought sensored were the best option because I figured out that it had to do some kind of feedback or something, but then I see that in this thread (https://www.rcgroups.com/forums/showthread.php?t=140454), where there are a lot of BLDC desings, there is only 1 sensored desing. So which is the best? What are the differences between them? I'm pretty lost, I would appreciate some help.

Thanks.
Last edited by h_e_c; Jul 09, 2012 at 02:20 PM.
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Jun 26, 2012, 07:34 PM
Emress
you want to use sensor less 3 phase brushless motors for a multirotor. check out hobbyking.com for some examples.

sensorless use a kind of feedback circuit on the ESCs to tell where the motor is in its rotation.

sensored use hall sensors to detect the magnetic fields of the magnets in the motor, and therefore the position of the motor in its turn.

for a 3 phase ESC, you'll need 6 MOSFETs. 3 PNP, 3 NPN type here are some basic schemes: http://www.uaelec.com/English%20expr...lease/BLDC.htm
https://www.rcgroups.com/forums/show....php?t=1490740
http://code.google.com/p/qut-brushle...er/wiki/mosfet
Jun 28, 2012, 07:39 AM
Registered User
Thread OP
Thanks for the links! The third one is really a treasure. It is all very well explained and step by step, although there are some things that I don't get:

It is written that in the motors there are only two wires activated at each time (that is 4 coils) to make the magnets spin, and that the cycle is repeated all the time commutating the different wires. We are also told that the activated coils will suffer the back-EMF and that the other two that are free will not (though I still can't understand), so that is our feedback. But that seems only to work into a BL motor with 6 coils , because in this one (an average one) there are surely more than 6 coils. Then why is still a 3-phase motor if it has more than 3 wires and 6 coils?

The other thing I don't get is the MOSFET driving. What are the MOSFETs in this image (http://dl.dropbox.com/u/6783818/Brus...s/complete.png) connected to the output to controle the PWM voltage that goes to the motor? In the first link you gave me (http://www.uaelec.com/English%20expr...lease/BLDC.htm) the MOSFETs function is much more clear: to control the PWM signals from the Atmel or others to make the motor run OK. But in the third link the PWM signals seem to be directly connected to the motor without being adapted, and the PWM signals seem to go directly to the analogic input of the MCU! I have to be interpretating the circuit wrong but I can't figure where.

Please all help is welcomed. Thanks.
Jun 28, 2012, 01:38 PM
Emress
first off, here are more links that i found when i was interested in DIY ESCs
http://blog.spingarage.com/build-a-d...troller-in-a-d
https://www.rcgroups.com/forums/showthread.php?t=140454
http://pcbheaven.com/wikipages/How_B...s_Motors_Work/
http://www.rcuniverse.com/forum/m_1558046/tm.htm
http://www.instructables.com/id/BLDC...otor/?ALLSTEPS
http://elabz.com/bldc-motor-with-ard...-and-software/
http://elabz.com/brushless-dc-motor-with-arduino/
http://blog.spingarage.com/58108473
http://what-when-how.com/electric-mo...lectric-motor/
http://www.bavaria-direct.co.za/models/motor_info.htm

Quote:
It is written that in the motors there are only two wires activated at each time (that is 4 coils) to make the magnets spin, and that the cycle is repeated all the time commutating the different wires. We are also told that the activated coils will suffer the back-EMF and that the other two that are free will not (though I still can't understand), so that is our feedback. But that seems only to work into a BL motor with 6 coils
half way through this info, you will see an animation of motor turning and which phase is high or low at each point in the turn. yeah so each pair of two coils is a phase, using some sort of hardware(look right above the WINDINGS section at the bottom of the post), you can read this EMF form the two activated phases and find out where it is in its spin. It isn't dependent on a 6 "coil" BLDC; BEMF is by the phases(which could be made up of two coils or cogs/teeth).

Quote:
Then why is still a 3-phase motor if it has more than 3 wires and 6 coils?
here, look at this:

it has 3 cogs (the things sticking out of the center) this would be the simplest 3phase motor you could get. it has one cog with wire wrapped around it per phase. i talk about how to connect the cogs later in this post. now look at the next picture:


it has 12 cogs, but it is still 3 phase because of the way it is wound. each phase(R, G ,B) has 4 cogs each to make up its phase so that each phase has the same number of cogs. phases are made up of different numbers of cogs depending on how many(cogs) there are in a motor.

I dont have a pic, but it would be similar for a 4-phase motor with 16 cogs. each phase would have 4 cogs evenly placed around the motor.


Quote:
The other thing I don't get is the MOSFET driving. What are the MOSFETs in this image (http://dl.dropbox.com/u/6783818/Brus...s/complete.png) connected to the output to controle the PWM voltage that goes to the motor? In the first link you gave me (http://www.uaelec.com/English%20expr...lease/BLDC.htm) the MOSFETs function is much more clear. But in the third link the PWM signals seem to be directly connected to the motor without being adapted, and the PWM signals seem to go directly to the analogic input of the MCU! I have to be interpretating the circuit wrong but I can't figure where.
ah yes, some of those schematics are not complete. this one is most likely what it would be in reality:
I'll explain it: the ATmega8(MCU) receives the pulse from the RX/FC/whatever then it calculates PWM values for how fast the motor is going/needs to go/where the motor is in its spin(according to feedback), it then generates a PWM pulse for the phases (atleast one is LOW) and sends them out. (another note; Arduino code is slow-ish depending on how you write the code )
the next part: the mosfet pairs for each phase receives the signal and and depending on the LOW/HIGH combo of the two MOSFETs of each phase, a +(high) or a -(low) bias is created on that phase
and the last part is the resistor network thing at the bottom. it is used to determine the BEMF so the MCU knows where the motor is in its spin. again, i dont know quite how this works.

WINDINGS
Another thing you should know about are the different winding styles: YWE/star and delta windings. and then there are two further subsets that apply to these: LRK and DLRK.

this is what star/YWE looks like on the left, and Delta is on the right:

1, 2, 3 are the 3 phase wires. they are LRK winds.

Delta LRK:


Star LRK:


Delta DLRK:


star DLRK:


9 cog delta:


9 cog star(WYE):


i cant quite remember, but i think Delta is better overall than star(WYE). You can see in the Delta LRK with 12 cogs that it doesnt fill in all the cogs, i dont know if this is better for some rare case, but the more wire the better the motor will be (aka, fill in all the cogs) .

Read the post then go back and it will make more sense as your questions are intertwined.

also, you'd be better off in this forum: https://www.rcgroups.com/electric-mo...struction-361/ but its too late, so you could just make a new topic there and put the link to this topic in that topic (people dont like double posting )
Last edited by sirbow2; Jun 28, 2012 at 02:19 PM.
Jun 29, 2012, 04:54 AM
Registered User
Thread OP
Wow, thank you very very much for all this info! These are the answers that make you love the help in the forums.

What I quite don't get yet is the MOSFETs signals. In the animation in this link you've put (http://elabz.com/brushless-dc-motor-with-arduino/) it is written that the motor (which is in star WYE) uses a high output coming from the MOSFETs to activate the coils in A and B are high and they make the north pole in the exterior part of the coils to be attracted by the south pole of others. Then in C the signal is low (0). But that is only because the North pole of the coils is always fixed. Or can it be reversed? If the high input does always make the north or south pole in the same place (that is what I think) then the coils have only two states: on (with a fixed an always the same polarity) and off. Am I right? And then the other three free coils are used to make the feedback to the resistors and then to the MCU, right? But then why are the MOSFETs connected to the input of the MCU if they are not involved into feedback? What's more, why are they just there? Couldn't just let the PWM go to the motor directly? Or is the MOSFET a way to adequate the voltatge to the motor?

But another problem is that the MOSFETs are inverters: if it enters a 1 then the output will be 0. So in fact the low input in the motor is a high output from the MCU, unless it is mounted in a structure which is a buffer. If not, does the MCU invert the logic automatically?

Then, about the delta WYE and delta DRLK connections, which is the best? How can I know if the motor I'm buying is one type or another? Is it possible to change the type?

About the slow of the Arduino, I'm not going to program it, I'll just use the Multiwii 2.0 version and try to interpretate the most as I can.

Thank you again.

PD: I'm sorry but I haven't been able to find the thread that you mention . Your link leads me to a whole page of threads and I don't know which is the one you meant. I also don't like double posting (I promise you I've searched quite a lot before posting, but the info was to advanced for me), but I need the name of the thread so I can do that.
Last edited by h_e_c; Jun 29, 2012 at 05:22 AM.
Jun 29, 2012, 11:37 AM
Emress
Quote:
Or can it be reversed?
you can turn the motor a differnt way by inverting that signal HIGH/LOW table for the 3 phases. but it is easier to just switch any two of the three wires conencted to the ESC from the motor and that will cause it to go the other way.

Quote:
then the coils have only two states: on (with a fixed an always the same polarity) and off. Am I right?
yes, each phase can either be HIGH or LOW

Quote:
And then the other three free coils are used to make the feedback to the resistors and then to the MCU, right?
im a little rough on this subject, but yes, the two phases are powered, and as the last phase goes by the magnets, it generates a little voltage that is measured by MCU. i searched BLDC sensorless BEMF an got some very helpful info. among them:
http://bldc.wikidot.com/bldc-and-8051
http://ww1.microchip.com/downloads/e...tes/01160A.pdf
http://cache.freescale.com/files/product/doc/AN1913.pdf

Quote:
why are the MOSFETs connected to the input of the MCU if they are not involved into feedback? What's more, why are they just there?
the mosfets are not connected to a input pin... those are digital pins used for PWM output. although you can use analog pins for digital reading/writing as the same as digital pins(think arduino for ex)

Quote:
Couldn't just let the PWM go to the motor directly? Or is the MOSFET a way to adequate the voltatge to the motor?
MCUs function at 5v and even 3.3v most of the times and most motors are 3s(12.6v fully charged) for a common quad. not to mention the crazy amount of amps these things draw which is 60+ amps commonly( as a whole, my quad is 18amps a motor). and MCU pins are 5/3.3v and about 40MILIAMPS per pin. this obviously no where close to what a BLDC needs. simplified: so a mosfet which is triggered by the MCU is connected to the power source(a battery etc) and the "other end" is connected to the motor which allows lots of current and a higher voltage.

first off, there are two types of mosfets(for how you trigger them): logic level and "regular". Logic level mosfets have something called a charge pump inside them so that 3.3/5v logic voltage can trigger them fully. regular mosfets, though, dont have these charge pumps and to fully "open"(open meaning least amount of resistance for the power flowing through them), a regular mosfet requires a voltage to open the "gate" that is the same as the voltage that is going through it. so if you have a 12v motor, you need a 12v trigger to open the mosfet. now on to how this applies to MCUs.

The mosfets are connected to either a mosfet driver or some smaller transistors or they are logic level Mosfets. A mosfet driver is a IC that takes the low(3.3/5v) voltage from the MCU and also takes the higher voltage that is needed to trigger the mosfet fully. it then has some sort of transistor inside that is switched by the 3.3/5v and puts out the higher voltage to the mosfet gate, thus the gate is fully opened using a sort of charge pump. logic level mosfets, as i said before, can be directly opened fully with a MCU. this is just the basics, there are current limiting resistors, caps and other stuff that goes with these ICs/mosfets etc. sometimes people use PNP/NPN simple transistor to do this also.
look here: http://www.diydrones.com/profiles/bl...toquad-esc32v2 at this pic:

http://api.ning.com/files/ZEsVn8e-qL...__/ESC_btm.jpg the pic wont display here hmm... click on the link
you can see the big mosfets at the top and then the IR2301S which are the mosfet drivers which trigger the mosfets from the MCU voltage..

let me know if you want to know the difference between NPN/PNP types

Quote:
I'm sorry but I haven't been able to find the thread that you mention . Your link leads me to a whole page of threads and I don't know which is the one you meant. I also don't like double posting (I promise you I've searched quite a lot before posting, but the info was to advanced for me), but I need the name of the thread so I can do that.
i meant make a new topic in that forum and put a like there to here those guys dont come here very often from that forum.

Quote:
Then, about the delta WYE and delta DRLK connections, which is the best? How can I know if the motor I'm buying is one type or another? Is it possible to change the type?
that was just extra motor info. doesnt really matter. a ESC works for any of : delta/WYE/dlrk/lrk (only really need to know this if if you burn out a motor and dont want to buy another)


Quote:
WYE and delta DRLK connections
i think you go it messed up. WYE(star) and delta are the two types of winds. as you can see they end the wires differently in the motor. i dont know a really good explanatio for this, but i think i could say DLRK is just a way to use standard LRK WYE/Delta on a motor with more cogs. i could use some more input on this from someone else
Last edited by sirbow2; Jun 29, 2012 at 11:53 AM.
Jun 29, 2012, 02:25 PM
Emress
i found some BEMF info for ya:
Quote:
You need 6 IO lines per motor, the fets can be switched at the same time. Back-emf signals look like sine waves 120 degrees out of phase, you must ground one coil, drive one, and back-emf sense on the third. When the back-emf wave crosses zero, you PWM the appropriate coil to achieve commutation. Then you listen on the next coil and repeat. From what I measured, ESCs use a 40khz PWM on each channel.
Jul 02, 2012, 05:55 PM
Registered User
Thread OP
Quote:
im a little rough on this subject, but yes, the two phases are powered, and as the last phase goes by the magnets, it generates a little voltage that is measured by MCU. i searched BLDC sensorless BEMF an got some very helpful info. among them:
http://bldc.wikidot.com/bldc-and-8051
http://ww1.microchip.com/downloads/e...tes/01160A.pdf
http://cache.freescale.com/files/product/doc/AN1913.pdf
Thanks for these links.

Quote:
MCUs function at 5v and even 3.3v most of the times and most motors are 3s(12.6v fully charged) for a common quad. not to mention the crazy amount of amps these things draw which is 60+ amps commonly( as a whole, my quad is 18amps a motor). and MCU pins are 5/3.3v and about 40MILIAMPS per pin. this obviously no where close to what a BLDC needs. simplified: so a mosfet which is triggered by the MCU is connected to the power source(a battery etc) and the "other end" is connected to the motor which allows lots of current and a higher voltage.

first off, there are two types of mosfets(for how you trigger them): logic level and "regular". Logic level mosfets have something called a charge pump inside them so that 3.3/5v logic voltage can trigger them fully. regular mosfets, though, dont have these charge pumps and to fully "open"(open meaning least amount of resistance for the power flowing through them), a regular mosfet requires a voltage to open the "gate" that is the same as the voltage that is going through it. so if you have a 12v motor, you need a 12v trigger to open the mosfet. now on to how this applies to MCUs.

The mosfets are connected to either a mosfet driver or some smaller transistors or they are logic level Mosfets. A mosfet driver is a IC that takes the low(3.3/5v) voltage from the MCU and also takes the higher voltage that is needed to trigger the mosfet fully. it then has some sort of transistor inside that is switched by the 3.3/5v and puts out the higher voltage to the mosfet gate, thus the gate is fully opened using a sort of charge pump. logic level mosfets, as i said before, can be directly opened fully with a MCU. this is just the basics, there are current limiting resistors, caps and other stuff that goes with these ICs/mosfets etc. sometimes people use PNP/NPN simple transistor to do this also.
look here: http://www.diydrones.com/profiles/bl...toquad-esc32v2 at this pic:
Then I guess that in the example circuit (http://dl.dropbox.com/u/6783818/Brus...s/complete.png) the NPN transistor has to be fully charged up, so that's why we build that transistor-network. But then what the heck are the N-MOS and the P-MOS? Logic level MOSFETs? But if it was that there wouldn't be the need of a network. I'm messed up here, what difference are between them? Maybe the N-MOS is a vacuum triode or something similar?

And another question, does the same PWM signal goes into the two transistors, the NPN and the P-MOS, which the signal comes from two different outputs? In the example circuit, I mean. So in the picture, is PWM 1 the same as PWM 2?

And another thing that still don't get: if the PWM goes up, the motor goes up (in rpm). But, if the MOSFET receives a high PWM, it will invert it and send a low output. Because if Vin > Vt, then Vout = (V+ * Ron)/(Ron+Rpul). But then if it recieves Vin > Vt, we know that the MOSFET acts like a short circuit. So in that case the Vout = V+ - Vrpul. That is higher that the Vout when the MOSFET receives a logical one. Does that works like this? And if it does, does the MCU software have to take care of it? I'm probably asking a stupid or novice question , but I can't figure out a different way of how it works, except if the network inverts it again so the overtop logic remains the same. (With Rpul I refer to the common Pullup resistance used in the MOSFETs)

https://www.dropbox.com/s/sofi4v35uz...t_function.jpg

Quote:
let me know if you want to know the difference between NPN/PNP types
Yes please, that would be great. I've looked around but I still don't know its differences.

Quote:
i found some BEMF info for ya:
Quote:
You need 6 IO lines per motor, the fets can be switched at the same time. Back-emf signals look like sine waves 120 degrees out of phase, you must ground one coil, drive one, and back-emf sense on the third. When the back-emf wave crosses zero, you PWM the appropriate coil to achieve commutation. Then you listen on the next coil and repeat. From what I measured, ESCs use a 40khz PWM on each channel.
Hmmm, now I get it... Although there is still something doesn't quite fit into this google code project (http://code.google.com/p/qut-brushle...ki/mosfetdrive) because it says that the fets CANNOT be switched at the same time because they will create a short and explode. And also in this link (http://elabz.com/brushless-dc-motor-with-arduino/) they tell you that you use TWO coils activated, and the third is the back-EMF one. I don't get it because there are different opinions, but in the first link it is written that the MOSFETs may explode if they are switched all together making a short. Any explanation?

Thanks and regards.

PD: Now it's very late and I'm so tired, by I'll post in that part of the forum a link to this thread as soon as I can.
Jul 02, 2012, 10:34 PM
Emress
Quote:
Then I guess that in the example circuit (http://dl.dropbox.com/u/6783818/Brus...s/complete.png) the NPN transistor has to be fully charged up, so that's why we build that transistor-network.
A P-MOS is a PNP type mosfet. like a regular pnp transitor but bigger. i think i have a possible explanation. for MCUs like arduino/stm32 for ex can only generate positive PWM(0v, +v,0v etc) where as negative PWM would be 0v, -v, 0v, -v. so, yes, the NPN is there so that a positive PWM can be used on a PNP. also, im guessing that those mosfets are logic level ones as if they weren't, the N-mos(npn) wouldn't be able to fully turn on(would need 12v, if it were not logic level) and its driven directly off of the MCU with a current limiting resirstor so the gate doesn't draw too much current for the pin MCU. maybe i dunno

Quote:
But then what the heck are the N-MOS and the P-MOS? Logic level MOSFETs?
they are like NPN/PNP transistors but mosfets are commonly called NMOS/PMOS or P mosfets/N mosfets.

Quote:
And another question, does the same PWM signal goes into the two transistors, the NPN and the P-MOS, which the signal comes from two different outputs? In the example circuit, I mean. So in the picture, is PWM 1 the same as PWM 2?
For each 2 mosfet pair of the 6 mosfet total, only one is on at one time in each pair of mosfets(phase), but not all are necessarily on. Think about how the phases inside the motor work; all the phases are inter connected so that when one phase has a negative bias, and another phase has a positive bias(and the other is off), it completes the circuit inside the motor and turns it with the magnetic field. These bias' are created by one mosfet being on of the 3 pairs on the ESC. the PMOS is connected to V+ of the battery and the NPN is connected to V-. if both of these were on it would be like connecting the + and - of a battery, and so the mosfets go boom(and not the whole battery). look at the first picture attached, it should help to apply it.
actually ill just draw it out:

so the top pair of mosfets: the MCU is sending a High(pwm) signal to the NPN which is then activated and pulls the Pmos low(pNp) to activate it. the Nmos is sent a Low signal to completely disable it(nPn means it would be on if it received a High signal). so that is sending a current to the 2 phase.
middle Mosfets: oppsosite of the top mosfets. the Pmos is sent a low signal(completley off, pNp), and the Nmos is sent a high signal so now it is on(nPn). so it has a - bias. now the circuit is complete electrons flow through from the + of the battery, through the mosfet, into the motor phase 2 and out phase1 and through the Nmos to the - side of the battery,
Third set of Mosfets: these are all off so no current flows in or out of this phase. this phase is used for BEMF.



Quote:
Although there is still something doesn't quite fit into this google code project (http://code.google.com/p/qut-brushle...ki/mosfetdrive) because it says that the fets CANNOT be switched at the same time because they will create a short and explode. And also in this link (http://elabz.com/brushless-dc-motor-with-arduino/) they tell you that you use TWO coils activated, and the third is the back-EMF one. I don't get it because there are different opinions, but in the first link it is written that the MOSFETs may explode if they are switched all together making a short. Any explanation?
this is explained in the previous quote. my guess on the BEMF would be that two are on(one phase + biased, and one - biased) and read the third as he said: "ground one coil, drive one, and back-emf sense on the third" it would make sense.

Quote:
difference between NPN/PNP types

the top pics are what they look like inside. the three pins are called Base, Emitter, Collector. i find these make most sense on the NPN type, but PNP confuses me(emitter at V+???, collector makes more sense)
Inside as you can see in the middle of the picture is what the transistors look like inside. it like a sandwich: a NPN has a Negative substance layer, then a P(the switch), and another N layer for output. when the P layer is driven high(on, because it is 'P'), that links the two outer layers and lets electricity flow. the last images show examples of how to connect it. this is where it is easiest to see the difference; PNP go on the "high" side- they switch + on and off. NPNs are on the low side and they switch the - side on and off. if one both arent connected(+ and -) then it doesn't work obviously because the electron cant move from + to -. it also says protection diode if needed; this means if you have an inductive load(motor, solenoid etc) you need a diode there to protect from feedback high voltage spikes.

opposite for PNP: p layer, n layer(lets electricity flow when low), p layer.
Pmos/PNP - on low(N), off high
Nmos/NPN - on high(P), off low


Pmos(PNP) needs NPN so it can turn on completely(pulls the Pmos(PNP) low). Nmos needs a PNP to pull it high to shut it off.
Last edited by sirbow2; Jul 02, 2012 at 10:55 PM.
Jul 05, 2012, 12:59 PM
Registered User
Thread OP
Quote:
For each 2 mosfet pair of the 6 mosfet total, only one is on at one time in each pair of mosfets(phase), but not all are necessarily on. Think about how the phases inside the motor work; all the phases are inter connected so that when one phase has a negative bias, and another phase has a positive bias(and the other is off), it completes the circuit inside the motor and turns it with the magnetic field. These bias' are created by one mosfet being on of the 3 pairs on the ESC. the PMOS is connected to V+ of the battery and the NPN is connected to V-. if both of these were on it would be like connecting the + and - of a battery, and so the mosfets go boom(and not the whole battery). look at the first picture attached, it should help to apply it.
actually ill just draw it out:



so the top pair of mosfets: the MCU is sending a High(pwm) signal to the NPN which is then activated and pulls the Pmos low(pNp) to activate it. the Nmos is sent a Low signal to completely disable it(nPn means it would be on if it received a High signal). so that is sending a current to the 2 phase.
middle Mosfets: oppsosite of the top mosfets. the Pmos is sent a low signal(completley off, pNp), and the Nmos is sent a high signal so now it is on(nPn). so it has a - bias. now the circuit is complete electrons flow through from the + of the battery, through the mosfet, into the motor phase 2 and out phase1 and through the Nmos to the - side of the battery,
Third set of Mosfets: these are all off so no current flows in or out of this phase. this phase is used for BEMF.
Thank you very very much again. As a student I appreaciate all this help. Your explanations are fantastic, now I do understand all the MOSFET bussiness. I was confused first because the strange behavior of the P-MOS type, but now I know how it works your scheme is a great help and very visual, so I finally understand.

I wonder how good it's this structure. Do you recommend me to structure my ESC like this? And what do you think it's the best ESC model you've used? Because I've seen lots of ways to drive the MOSFETs (with chips, only a logic level MOSFET, this way, P-channel...), but I don't know which is the best.

Another thing I don't understant it's the V+ connection. I know we connect that to the positive terminal of the voltage. But how much voltage? It is not specificated. It is a bit messy in some situations. Like in this picture:



And in the whole example circuit:



Here, in the first picture we can see that the chip has to be connected to 10-20 V. But has the MOSFET to as well? If not, am I supposed to have two batteries, one for the MOSFET and another for the chip? And in the second picture, the chip has to be connected to 5 V. What about the MOSFET? Do I need 3 different batteries then? At least 2 different, one for the small MOSFET driver chip and another for the big one, no? How do I adapt the voltages and how much voltage do the MOSFETs need? I know it has to be a silly question, but I can't figure out how does this works.


Quote:
the top pics are what they look like inside. the three pins are called Base, Emitter, Collector. i find these make most sense on the NPN type, but PNP confuses me(emitter at V+???, collector makes more sense)
Inside as you can see in the middle of the picture is what the transistors look like inside. it like a sandwich: a NPN has a Negative substance layer, then a P(the switch), and another N layer for output. when the P layer is driven high(on, because it is 'P'), that links the two outer layers and lets electricity flow. the last images show examples of how to connect it. this is where it is easiest to see the difference; PNP go on the "high" side- they switch + on and off. NPNs are on the low side and they switch the - side on and off. if one both arent connected(+ and -) then it doesn't work obviously because the electron cant move from + to -. it also says protection diode if needed; this means if you have an inductive load(motor, solenoid etc) you need a diode there to protect from feedback high voltage spikes.
Referring to the NPN and PNP differences and structure, unfortunately I can't see the photo you uploaded. I'm a little confused too about the emitter at V+, but I guess that they just name it like this by convention, so there is not a lot of differences in theory between the MOSFETs.

Thanks again.

PD: I'm sorry for the delay in the response, but I've been very very busy. And now I'll put a link to here in that forum.
Jul 05, 2012, 01:30 PM
Emress
Quote:
I wonder how good it's this structure. Do you recommend me to structure my ESC like this? And what do you think it's the best ESC model you've used? Because I've seen lots of ways to drive the MOSFETs (with chips, only a logic level MOSFET, this way, P-channel...), but I don't know which is the best.
id say use some driver chips(like the IR2101 in the pic below) and some regular(non-logic level) mosfets. like the image we've been using but with driver ICs instead of the NPN transistor. sorta like the image in the next quote.


Quote:
Another thing I don't understant it's the V+ connection. I know we connect that to the positive terminal of the voltage. But how much voltage? It is not specificated. It is a bit messy in some situations. Like in this picture:
the V+ voltage is the voltage your motors run at. so, 12.6v (a fully charged LiPo) would be V+ for a 3s motor.

Quote:
Here, in the first picture we can see that the chip has to be connected to 10-20 V. But has the MOSFET to as well? If not, am I supposed to have two batteries, one for the MOSFET and another for the chip?
That 10-20v in the pic would also be connected to the battery if you had a 3s ESC. if you had a 2s ESC the driver ICs most likely that wont need 10+ volts for the IC, as that 10-20v is what triggers the mosfets from the logic voltage (MCU/Logic pins). so the 10-20v would be 8-15v(a 2s is 8.4v fully charged) for a 2s battery.

Quote:
And in the second picture, the chip has to be connected to 5 V. What about the MOSFET? Do I need 3 different batteries then? At least 2 different, one for the small MOSFET driver chip and another for the big one, no? How do I adapt the voltages and how much voltage do the MOSFETs need? I know it has to be a silly question, but I can't figure out how does this works.
3 batteries would be silly All ESCs have atleast two voltage regulators; one is for the the internal MCU that triggers the Mosfets, and the other vreg is for powering external things like a RX or a multirotor control board etc. the MCU vreg downsteps the 12.6v from the battery (same voltage that the mosfets switch on/ff for the motor phases) to a 5v or 3.3v that is MCU friendly. so one battery supplies 12v to all the ESCs which all have vregs for the internal MCU and external power uses.


Quote:
unfortunately I can't see the photo you uploaded.
hmm works for be, but does this work?


Oh, and, thanks a ton! you have helped me improve my knowledge of this and may attempt to build a simple low amp ESC!
Last edited by sirbow2; Jul 05, 2012 at 01:46 PM.
Jul 05, 2012, 05:16 PM
Registered User
Thread OP
Thanks for your answer.

Although I've understood a lot of things, there's one that I can't comprehend. In this scheme, we drive one coil, ground another and use the third for back-EMF. But that leads me to doubts I cannot solve. It is sure that the firs coil is used to move the motor. But what about the grounded one? Does it make the motor spin, as well? (because the electricity also passes by it). If it does, then there are only three steps in the motor function, because there will be always two coils on, right?



And this motor desing is not the same as the one seen here http://elabz.com/brushless-dc-motor-with-arduino/ . In that desing, there are steps with only three coils driven, and others with six coils driven. So that makes 6 steps instead of 3. I guess that's because it is a sensored brushless motor, no? Because if there are two coils with an input and the current goes out throught the last one that is undriven, there is no space for the back-EMF feedback, so they have to use hall sensors. Am I right?

Quote:
That 10-20v in the pic would also be connected to the battery if you had a 3s ESC. if you had a 2s ESC the driver ICs most likely that wont need 10+ volts for the IC, as that 10-20v is what triggers the mosfets from the logic voltage (MCU/Logic pins). so the 10-20v would be 8-15v(a 2s is 8.4v fully charged) for a 2s battery.
What do you mean with 3s and 2s? I don't understand it. And I've seen that the normal ESCs go from 25A to 35A. What does it mean? Which should I use?

Quote:
Oh, and, thanks a ton! you have helped me improve my knowledge of this and may attempt to build a simple low amp ESC!
You're welcome! I should thank you, not vice versa! xD

Thanks and regards.
Jul 05, 2012, 06:25 PM
Emress
Quote:
In that desing, there are steps with only three coils driven, and others with six coils driven. So that makes 6 steps instead of 3. I guess that's because it is a sensored brushless motor, no?
this is how a 9 cog brushless motors current flow would go. with one driven(meaning one side of the phase is connected to V+ through a mosfet), and one grounded(the other phase connected to gnd through a mosfet).


Quote:
Although I've understood a lot of things, there's one that I can't comprehend. In this scheme, we drive one coil, ground another and use the third for back-EMF. But that leads me to doubts I cannot solve. It is sure that the firs coil is used to move the motor. But what about the grounded one? Does it make the motor spin, as well? (because the electricity also passes by it). If it does, then there are only three steps in the motor function, because there will be always two coils on, right?
explained above. it may help if you stop thinking of them as coils as there are 3 phases but can be 3 coils or 9... the third one is not driven or grounded(doesnt move motor, if it was driven it would stop the motor) and is used for BEMF. its "empty" because there is no where for the current to go(well besides the BEMF).

Quote:
What do you mean with 3s and 2s? I don't understand it. And I've seen that the normal ESCs go from 25A to 35A. What does it mean? Which should I use?
LiPos are categorized by "s". 1s is a battery that has 1 cell and is 4.2v fully charged. 2s would be two cells and 8.4v fully charged, 3s is three cells and so on. but its kinda funky. 3.7 is a standard voltage for each cell and that is how the voltage is displayed on the specs(3.7 for 1s, 7.4 for 2s...) so if you find a 2s battery, it will say 7.4v 2s
Jul 06, 2012, 08:11 AM
Registered User
Thread OP
Quote:
LiPos are categorized by "s". 1s is a battery that has 1 cell and is 4.2v fully charged. 2s would be two cells and 8.4v fully charged, 3s is three cells and so on. but its kinda funky. 3.7 is a standard voltage for each cell and that is how the voltage is displayed on the specs(3.7 for 1s, 7.4 for 2s...) so if you find a 2s battery, it will say 7.4v 2s
Hmmm, OK. But what about the bussiness of 25A and 30A in the ESCs? What does that mean? And what does "C" mean in a battery? I've been looking for batteries and I found this https://www.hobbyking.com/hobbyking/s...arehouse_.html.
2.2 Amperes, 3s, 11.1 v. That's pretty clear. But then what does "35C - 70C" mean?

Quote:
this is how a 9 cog brushless motors current flow would go. with one driven(meaning one side of the phase is connected to V+ through a mosfet), and one grounded(the other phase connected to gnd through a mosfet).



Quote:
Although I've understood a lot of things, there's one that I can't comprehend. In this scheme, we drive one coil, ground another and use the third for back-EMF. But that leads me to doubts I cannot solve. It is sure that the firs coil is used to move the motor. But what about the grounded one? Does it make the motor spin, as well? (because the electricity also passes by it). If it does, then there are only three steps in the motor function, because there will be always two coils on, right?

explained above. it may help if you stop thinking of them as coils as there are 3 phases but can be 3 coils or 9... the third one is not driven or grounded(doesnt move motor, if it was driven it would stop the motor) and is used for BEMF. its "empty" because there is no where for the current to go(well besides the BEMF).
I think you misunderstood my question because I did not expressed well. I wasn't referring to the coils, I was referring to the phases. In fact is a quite silly question but I still have the doubt. I was saying that the driven phase (connected to V+) was surely with its coils magnetized. But what about the grounded phase? The current passes by as well, does it have its coils activated? And they could be activated, but with the poles inversed, as the current passes in the opposite direction, no?

And my other doubt referred to this link and its animation http://elabz.com/brushless-dc-motor-with-arduino/. There, we see a signal table for every motor step:



Here, in the table, we see that there are steps with TWO high signals entering the motor in A and B. These signals have to go to ground so the current can pass through its coils. But the only way to do that is the remaining C, so that is the grounded phase. If there is not other phase to do that, then there is no space for back-EMF so this must be a sensored brushless ESC. Am I right? My question was that, because in our desing there are always 1 high, 1 low, 1 off. So the desing in the link has to be sensored because if not there would be no feedback.

That was my main question. The secondary question is the one made above: Are the coils of the grounded phase working? I guess so, because current passes by. But the direction of the current is inverted then, so wouldn't they counteract to the driven phase coils?

Thanks for your patience, I know the question is a bit messy.

Edit: The image is not visible, I'll attach it.
Jul 06, 2012, 01:25 PM
Emress
Quote:
Hmmm, OK. But what about the bussiness of 25A and 30A in the ESCs? What does that mean?
Ah forgot to answer that didnt i it is the max amp rating the ESC is good for. this is similar to the battery rating thing below. if your motors draw 18A you dont want a 18A ESC(stress etc), you would want a 25A ESC.

Quote:
And what does "C" mean in a battery? I've been looking for batteries and I found this https://www.hobbyking.com/hobbyking/s...arehouse_.html.
2.2 Amperes, 3s, 11.1 v. That's pretty clear. But then what does "35C - 70C" mean?
that is the discharge rate. if you have a 2200mah(miliamphour) battery, that is 2.2ah(amphour) and 2.2ah * a 25c rate = 55A max discharge rate from the battery(aka the four motors shouldnt draw any more than 55A. its always good to choose a C rate that is 10 over the minimum C rate you need. so if you have a 2.2ah battery and you need at most 55A current draw(25c), you should get a 35c battery. so that battery you have there can do 77A continuous and 174A burst.

there is also a charge rate that is most times found on the back of the battery. i like to charge mine at 2c or 2.2ah *2c = 4.4A charge rate in amps on the charger, that is if you have a 2.2ah battery.

Quote:
I was saying that the driven phase (connected to V+) was surely with its coils magnetized. But what about the grounded phase? The current passes by as well, does it have its coils activated? And they could be activated, but with the poles inversed, as the current passes in the opposite direction, no?
the current goes through at least two phases. for ex, it flows from V+ in phase 1, through Phase 2(because they are connected inside the motor) to ground(aka V-). its not just the phase that has V+ connected to it that is magnetized; those two whole phases are magnetized because the current is flowing through them from V+ to V-.
You could think of it as an electromagnet; one side(phase1) is connected to V+ and the other(phase2) to ground(V-). the whole coil of the magent produces a magnetic field, not just half of the coil.

Quote:
Here, in the table, we see that there are steps with TWO high signals entering the motor in A and B. These signals have to go to ground so the current can pass through its coils. But the only way to do that is the remaining C, so that is the grounded phase. If there is not other phase to do that, then there is no space for back-EMF so this must be a sensored brushless ESC. Am I right? My question was that, because in our desing there are always 1 high, 1 low, 1 off. So the desing in the link has to be sensored because if not there would be no feedback.
this is somewhat similar to the previous answer. for ex, current flows through phase 1/2 from V+, and since all three phases are interconnected, the current flows through Phase 3, which is connected to ground(aka V-) through the mosfet, from phases 1/2.
It is still definitely a brushless sensorless motor. although im not quite sure how the BEMF thing works when two phases are high and one is grounded.

Quote:
That was my main question. The secondary question is the one made above: Are the coils of the grounded phase working? I guess so, because current passes by.
i said this above but i will explain it quick again. current is coming from phase A/B and flowing to ground on phase C. look at the arrows right below the High/Low words and to the right of IA/B/C; they point in the direction of the current flow for that phase. It wouldnt make sense for the current to "pass by" the ground wire and flow from V+(high) to V+(high). Current must flow to ground from V+. i think this is where you're getting mixed up the most: current flow.


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