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Old controller with coreless motors.


johnarcher
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I think one thing that has confused some people is that they think a coreless motor is brushless.

All DC motors must have brushes. AC motors usually don't but can have.

Even what is called a "Brushless" DC motor (BLDC) isn't a DC motor at all as it is a type of AC motor with a driver board to convert the DC into a form of AC (pulses, whatever)

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6 hours ago, maico said:

 

You could do but aliaexpress is full of fake and used stuff. These are fakes for example...

 

I was somewhat surprised by the £3.74 price - I remember Maxons being somewhat more pricey when I used to use them!

 

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2 hours ago, AndyID said:

 

and even then if you run the poor thing into the buffers and it stalls it's likely to overheat. Ideally you want a controller with sensitive over-current protection.

I'm old fashioned. All my portescaps have a 250ma (I think) fuse.

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27 minutes ago, melmerby said:

I think one thing that has confused some people is that they think a coreless motor is brushless.

All DC motors must have brushes. AC motors usually don't but can have.

Even what is called a "Brushless" DC motor (BLDC) isn't a DC motor at all as it is a type of AC motor with a driver board to convert the DC into a form of AC (pulses, whatever)

Coreless motors don't have brushes. They use gold wipers.

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41 minutes ago, sharris said:

 

I was somewhat surprised by the £3.74 price - I remember Maxons being somewhat more pricey when I used to use them!

 

I suspect they are a batch of surplus as the quantity is somewhat limited compared to most "Made in China" stuff, legit or otherwise.

There are plenty more in the £30+ bracket.

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14 hours ago, Denbridge said:

Coreless motors don't have brushes. They use gold wipers.

 

You mean they have gold brushes. Brushes do not need to be carbon.

 

Which reminds me, someone, in one of the scale societies I think, investigated coreless failures and it was the flimsy brushes that were the failure point, not the armature windings.

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On 12/10/2019 at 03:09, Crosland said:

 

You mean they have gold brushes. Brushes do not need to be carbon.

 

Which reminds me, someone, in one of the scale societies I think, investigated coreless failures and it was the flimsy brushes that were the failure point, not the armature windings.

 

Ah, but all that glitters is not gold. A few microns of gold-plating isn't going to survive for very long.

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On 12/10/2019 at 11:09, Crosland said:

 

You mean they have gold brushes. Brushes do not need to be carbon.

 

 

Gold doesn't seem to me a good material for motor brushes as it is easily worn down.

We had a lot of trouble where I worked with gold contacts wearing through on such things as switch wipers.

It's great for things that are only occasionally separated like plug-in board conectors or multiway sockets.

Edited by melmerby
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More than a decade ago Marklin introduced what they call Softdrive Sine AC motor. No commutators or brushes to wear out. The 12 pole magnets are skewed to reduce cogging at low speed.

 

 

Edited by maico
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2 hours ago, maico said:

More than a decade ago Marklin introduced what they call Softdrive Sine AC motor. No commutators or brushes to wear out. The 12 pole magnets are skewed to reduce cogging at low speed.

 

 

But no good  for a DC supply!

 

Another brushless design is this multipole motor which is driven by a 3 phase signal from a control IC:

capstan_motor.jpg.55f5edf8f83d0ab827afca4cd032b2b1.jpg

 

With the rotor on:

1864269390_motor2.jpg.f044f63ea8958d9bd7503e3f6f10c5bd.jpg

 

The magnet(s) are a ceramic ring. Speed is monitored by a hall device.

It is very smooth running.

It runs off 12v DC and I'm trying to find a model railway use for it!

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I spent the last few years before quitting the day job on the control of BLDC motors, but they were powered from a 400V DC bus. That *hurts*, even just across the end of a finger.

 

All you ever wanted to know about motor control but were afraid to ask: http://www.ti.com/download/trng/docs/c2000/TI_MotorControlCompendium_2010.pdf

 

 

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On 11/10/2019 at 20:43, melmerby said:

What is the difference?

The one I posted pictures of doesn't have gold anything.

 

The gold brushes, allegedly, are the parts that fail if a motor is used used with the wrong type of feedback controller. Pulse-width modulation at low frequency lets the  motor accelerate and decelerate many times a second and the gold brushes don't like this; they are rated for a limited number of stops and starts. AFAIK the carbon brushes don't mind stops and starts, being mechanically more robust.

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1 hour ago, Guy Rixon said:

The gold brushes, allegedly, are the parts that fail if a motor is used used with the wrong type of feedback controller. Pulse-width modulation at low frequency lets the  motor accelerate and decelerate many times a second and the gold brushes don't like this; they are rated for a limited number of stops and starts. AFAIK the carbon brushes don't mind stops and starts, being mechanically more robust.

As has been mentioned before, gold is poor as a material for motor brushes, it will wear away very quickly, the one I dismantled had silver (by the look of it).

The motor cannot accelerate and decelerate many times a second as even with the reduced rotor mass of a coreless motor there is enough mechanical inertia to prevent it happening.

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2 hours ago, Guy Rixon said:

The gold brushes, allegedly, are the parts that fail if a motor is used used with the wrong type of feedback controller. Pulse-width modulation at low frequency lets 

 

It's also (if not primarily) the current surges on each pulse that are the problem, especially when starting or at slow speed when there is little or no Back EMF. 

 

High frequency pulses are smoothed out by the motor's inductance and look more like DC, at a much lower voltage.

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On 28/11/2019 at 14:48, willjam39 said:

Sorry to ask a question that i am sure has been asked before (but i cant find the answer). Is the Combi from Gaugemaster ok for coreless? 

The cream-coloured panel Gaugemasters are not feedback:image.png.7cfd41d989028a1f857520c7bc2f10d6.png

 

The black-panelled ones ARE feedback:  image.png.ea9d5259473c0ccafc41f8b8c9717207.png

 

 

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On 30/11/2019 at 23:29, DLT said:

The cream-coloured panel Gaugemasters are not feedback:

 

The black-panelled ones ARE feedback:  

 

 

 

where do you buy the black one? - even Gaugemaster don't show a black faced combi on their website :(

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The Gaugemaster "Black" hand held controller shown above is not a Combi.  It is their Model HH which is a Feedback type and has a four core cable. Two cores Yellow and Blue are connected to a nominal 16 volt AC supply (rated 14v to 18v AC) and the other two cores Red and Black go to the rails it is to feed.  Their Model W is a non feedback controller again requiring a separate nominal 16v AC power source. Same wiring colours are used in the four core cable,

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2 minutes ago, cliff park said:

Can I go slightly off topic and ask :- If I have an engine in my hand how can I tell if it has a coreless motor?

You can't, unless the manufacturer says so, or you can see the motor.

A coreless motor will normally have a circular cross section (as the magnet is inside the coil):

51103-Coreless-Motors_Part1.png

A typical can motor has flattened sides due to the two magnets outside the coil.

These are Mashimas:

https://www.roxeymouldings.co.uk/category/42/motors/

 

However, in the case of Oxford Rail I was told the Dean Goods had a 5 pole quality iron cored motor, which was correct for the early ones. The later ones have a 3 pole coreless.

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