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ESCs and brushless motors


Gary Manuel
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The ESCs used for brushless induction motors generate a rotating magnetic field which rotates quicker as the demand increases.  Simple shaded pole induction motors as used in domestic appliances (at least at one time, I've no current experience) run at 3000rpm because the rotating magnetic field is created by the 50Hz mains.

 

Geoff

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Gary

A brushless ESC does not supply a conventional 3 phase supply as it just switches the DC supply on & off to each motor coil. The timing of each change is controlled by sensing the tiny EMF generated by the next unpowered coil. There is no external sensor to determine when the switch over needs to be made, hence the term "sensor less speed controller". The speed the motor runs at is regulated by how long the current it allowed to flow at each switchover.

 

A true marvel of electronics so its best just to let the ESC get on with it but it does perhaps explain why they can be a bit sensitive to even a slight poor connection and why they really do not like being over loaded in any way. 

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Thanks all.

 

I realised that the outputs of the ESC are "chopped" DC, rather than a sinusoidal wave. I've seen the term sensor-less but never appreciated what it meant, so thanks for the insight. As you say Simon, they are true marvels of electronics. It's nice to know what's going on under the bonnet, but sometimes it's best to just put your foot down and drive.

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3 hours ago, Gary Manuel said:

Thanks all.

 

I realised that the outputs of the ESC are "chopped" DC, rather than a sinusoidal wave. I've seen the term sensor-less but never appreciated what it meant, so thanks for the insight. As you say Simon, they are true marvels of electronics. It's nice to know what's going on under the bonnet, but sometimes it's best to just put your foot down and drive.

Just as a bit of extra info, I have attached a photo which shows my early "sensored" brushless motor and ESC which I bought in the early/mid 1990s (alongside a brushed motor of similar vintage). The motor has hall effect sensors built in with 5 wires connecting the sensor to the ESC.

 

I have seen our brushless motors referred to elsewhere as "electronically commutated DC motors", and that is actually a fairly accurate description.

 

Dick

Early motors.JPG

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5 hours ago, Geoff S said:

The ESCs used for brushless induction motors generate a rotating magnetic field which rotates quicker as the demand increases.  Simple shaded pole induction motors as used in domestic appliances (at least at one time, I've no current experience) run at 3000rpm because the rotating magnetic field is created by the 50Hz mains.

 

Geoff

In the days when washing machines only needed single speed motors, they nearly all used 1/4 or 1/3 HP single phase induction motors. The motors ran at 1500 rpm - slip, IIRC 1250rpm. Vacuum cleaners, spin dryers & any other appliances that needed higher rpm generally used brushed motors, which didn't have speed determined by the supply frequency.

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I'm sure you're right, Pat.  It's so long since I had anything to do with single phase motors I've forgotten.  They were also used in cheap portable record players (eg Dansette).  We had 3 phase at the shop and when dad retired and moved to a bungalow he had problems getting his tools (lathe circular saw etc) to work as the electricity board refused to install 3 phase ?

 

Our first washing machine was a twin tub Electrolux we bought s/h which used ac/dc motors ie brushed which I had to replace several times.

 

Brushless ESCs are a marvel.  I would have no idea how to design one.  No wonder they were so expensive 15 years or so ago.

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3 minutes ago, Redex said:

Maybe a suggestion to RCM&E for the 'E' part of the mag - an explanation of ESC working and/or construction of an ESC.

The basics are quite simple as per the attached diagram. The complex bit is the micro processor and software that make the switches work at the correct time to both run the motor and also keep the magic smoke in ?.

 

Dick

ESC operation.jpg

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That sketch is exactly the sort of thing I was looking for on Google - and exactly what I was expecting to see. Answers both of my original questions. Thanks Dickw.

 

Is there any more detail where you found that sketch? I for one would be interested in learning more.

Edited by Gary Manuel
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1 hour ago, Gary Manuel said:

That sketch is exactly the sort of thing I was looking for on Google - and exactly what I was expecting to see. Answers both of my original questions. Thanks Dickw.

 

Is there any more detail where you found that sketch? I for one would be interested in learning more.

Unfortunately not, as I drew that one myself some time ago as the simplest illustration I could make of the basic principles.

 

Dick

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17 minutes ago, PatMc said:

@Dickw have you drawn a "star" (AKA "Y") winding connection for clarity in the explanation ?

I'm pretty sure most model motors use "delta".

I'm no expert (obviously) but I doubt it, as a Delta would not allow the 6 step control plus EMF feedback that I have been reading about and included in my link above.

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1 hour ago, PatMc said:

@Dickw have you drawn a "star" (AKA "Y") winding connection for clarity in the explanation ?

I'm pretty sure most model motors use "delta".

Yes, I chose a Star winding because I thought the parallel path in the Delta might distract people from the basic principle.

I think most motors do use a delta winding because it is simpler - i.e. just the 3 connections and no need to make a star point connection. However I am aware of Y wind motors, and Neu seem to do a fair few:-

https://neumotors.com/motors/neumotors-1210-series-bldc-motor-65-150-watts/

 

Dick

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1 hour ago, Gary Manuel said:

I'm no expert (obviously) but I doubt it, as a Delta would not allow the 6 step control plus EMF feedback that I have been reading about and included in my link above.

A lot of motors have a delta wind e.g I have several of these which as the name implies is a 2 turn Delta wind:-

http://support.jetimodel.cz/en/katalog/Motors/@produkt/Phasor-Race-2035-2100-2D/

 

Mine work very well up to 60,000 rpm with full throttle control, so obviously the ESC is keeping up with it.

 

Dick

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I've built & wound a couple of motors, one as delta connection only but as an experiment I tried both delta & star on the other. As I expected the star connection resulted in lower rpm/v & reduced max power. I used normal ESCs for both motors without any problem.   

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