Motor Controllers for Models and Tools

[Neil WyattModerator @neilwyatt]

Discussion of homebrew PWM and BLDC motor controllers

[Neil WyattModerator @neilwyatt]

Ok, looking around I have a few controllers based around logic-level FETs. I use AVRs to control them as they make PWM very easy and interface with all sorts of things (including my own wired controller and servo PPM signals). they leave plenty of options for bells and whistles. As far as the electronics are concerned the same simple 'power circuits' should work for many small motors.

Neil

[Neil WyattModerator @neilwyatt]

This is the Shunter's speed controller. It works, but I feel it is a rough prototype, not the finished thing.

The SMD components (uP and a few NPN transistors) are under the board. 12V 10A relays handle reversing and back EMF braking. The software ensures the relasy only wswitch when the FET is switched off.

Silver heatsink is a 7805 for the logic, which gets warmer than the switching FET! I can't remember what the two LEDs are for. One flashes when the control box is connected, I don't remember what the other does. I always hang a LED or two of spare uP pins -they look pretty and can be used for debugging.

There's an AVR in the control box as well, a primitive one as I wanted to use up some old chips.

The controls are probably self-explanatory, other people have found it easy to use.

I may convert to a rotary control, but still with a ramp up/down rather than instant response. There's a little green LED that flashes when connected as well as the display.. Two way coms mean I can add a battery monitor in the future.

Truckloads of room for future development, especially adding sound, battery status, current monitor and maybe a speed readout.

Edit – other improvements would be an H-bridge to get rid of the clunky relay, maybe with opto isolation, and an option to have a uni or bi-directional radio link for use pulling scale trains.

If all the goodies can be added and sorted for a small 10A or so controller, scaling up to one for a hefty 24V 50-100A controller would be relatively simple.

 

Neil

Edited By Neil Wyatt on 24/05/2014 17:47:20

[Ian PParticipant @ianp]

Neil

First line of your post starts 'This is'.

It sort of indicates that we should be able to see whatever 'is' is!

Did you mean to attached a picture, circuit diagram, or a link to?

Ian P

[Neil WyattModerator @neilwyatt]

Well spotted Ian, you found the deliberate mistake.

Here it is:

As you can see it's very prototype!

Neil

[John HaineParticipant @johnhaine32865]

Sorry Neil, have only been earning a living in electronics for 40 years, what's an AVR?

[Anonymous]

Posted by John Haine on 24/05/2014 22:52:53:

Sorry Neil, have only been earning a living in electronics for 40 years, what's an AVR?

It's a microcontroller family, Atmel if I recall correctly – Andrew

[RobboParticipant @robbo]

I suppose this all makes sense to you young folk!

Nurse, the screens!

[Neil WyattModerator @neilwyatt]

Sorry,

I use microcontrollers ('computers on a chip&#39 as the brains of my projects.

AVR is Atmel's microcontroller technology. It's a competitor to Microchip's PIC and is generally seen as more oriented to professional use with less support for the hobby side. Atmel provide brilliant tools and datasheets/appnotes. There's also a full implementation of the GNU C compiler chain (GNUCC/WinAVR).

**LINK**

The PIC architecture does have an awful lot more hobby support, but, at least in its earlier forms, is arguably less user friendly.

I suggest anyone wantiong to find out more googles Arduino or PicAxe

The AVR Arduino boards and PicAxe boards are a relatively easy way for those who want to get into these fascinating and flexible chips.

Neil

[Michael GilliganParticipant @michaelgilligan61133]

A request for advice, please …

A few years ago, I bought a Baldor Brushless AC ServoMotor [New, Old Stock] at what seemed to be a bargain price. … I then discovered the price of the proper controller for it; and it has since lain unused.

Can anyone suggest an "economy" method of driving it ?

Many thanks

MichaelG.

___________________

CAT. BSM80B-275AA

D1598071

SPEC S2P100N016Q1

MFG W038/0201

TORQ CONT. STALL 2.2 NM

CURR CONT. STALL 3.38 A RMS

RATED SPEED 4000 RPM

RATED BUS VOLTAGE 300 VOLTS

PEAK CURRENT 10 A RMS

CLASS 1 25°C AMB

MFD BY BALDOR ELECTRIC CO FT SMITH AR U.S.A NP0767

[Ian PParticipant @ianp]

Posted by Michael Gilligan on 25/05/2014 14:48:43:

A request for advice, please …

Brushless AC ServoMotor [

Can anyone suggest an "economy" method of driving it ?

Many thanks

MichaelG.

_

Michael

I hope you get some positive replies to your question. I am in the same position having a couple of large (2KW) brushless servomotors with no means to drive them, actually I do have one of the correct servo drives which I use with one of the motors and is currently powering my linisher! (Its massive overkill but the variable speed makes it into a very versatile machine)

The motors have optical encoders which are normally used to control the commutation, but it seems to me that it should be possible to power the motors using the same technology that is used on model aircraft brushless motors.

Ian P

[Neil WyattModerator @neilwyatt]

Do you need the servo speed control?

If its a straight 3-phase drive a 240V VFD/inverter might run it. I think they go up to 600Hz.

Neil

[Ian PParticipant @ianp]

No I dont need it to work as a servomotor, I would just want to be able to control speed.

I thought about using a VFD, if fact I tried the motor with a VFD but I could not make it run.

Afterwards I thought about it a little and realised that VFDs work with induction motors (current 'induced' into the rotor) whereas brushless servos have permanent magnets in the rotor. (Both those previous statements would be reversed with an 'outer rotor' motor.)

I dont know enough to work out the difference between 3 phase for an induction motor and 3 phase for a permanent magnet motor but there are millions of brushless small motors in everything from CD players to some of the newer battery drills and lot of them are self commutating. I am sure a beefier version of a model 'ESC' would work.

Ian P

[Neil WyattModerator @neilwyatt]

A bit of digging suggests you are right, it's probably effectively an 'ESC' on steroids you need. There are circuits on line, but I'd want to get more experience of low-voltage ESCs first.

Neil

[Michael GilliganParticipant @michaelgilligan61133]

Thanks Neil, and Ian

For info .. I believe this is the "next generation" but very similar to mine.

MichaelG.

[Neil WyattModerator @neilwyatt]

There may be an app note to suit here, if you can be sure which type of sensor your motor uses:

<edit> Sorry, no, they don't cover "BLAC".

Neil

Edited By Neil Wyatt on 25/05/2014 20:14:30

[Ian PParticipant @ianp]

The motors I have use an optical encoder as the sensor so a sensorless ESC would be the best route.

What is BLAC?

Ian P

[Neil WyattModerator @neilwyatt]

I used it for 'Brushless AC'.

I imagine the only real difference is that BLDC use a single supply while brushless AC motors apply positive and negative voltages. This would halve the maximum voltage to ground at the cost of a little more complexity in the control circuitry.

Using the sensor has the advantage that you don't have to fiddle about coming up with a starting algorithm, as the coils only generate enough back emf to synchronise the controller above a certain rpm. Not a big issue if the motor always starts on no-load or a constant load.

This is all gleaned from past reading of app notes – not practical experience.

Neil

[MuzzerParticipant @muzzer]

This is almost certainly a permanent magnet synchronous motor that needs to be driven by a sinusoidal waveform. You can check that by driving it (slowly!) and looking at the back emf if you have a scope handy, For a synchronous motor, you need to tell the motor drive the position of the rotor, hence the encoder, resolver or whatever. Presumably there is some form of position sensor on your motor?

BLDC motors are usually driven with fairly simple on/off waveforms and the position sensing can be much simpler ie Hall effect sensors buried in the motor. It's possible you have one of these but seems less likely.

VFDs are available with encoder inputs, so if you can find one of these you may have a solution. Judging from the voltage rating you will be using a VFD running directly from AC rather than through an isolation / reduction PSU – some servo systems run 48VDC or similar.

I've just been looking at something very similar myself from a local (to me) company **LINK** which would cost about 200 quid. It would almost certainly work with your motor although there may be something available more conveniently for you. I'm sure you could find something on ebay or Ali Express….

Murray

[Michael GilliganParticipant @michaelgilligan61133]

Thanks Murray,

I just had a quick look on ebay

… Baldor seems to hold its price rather well.

… Yes, it might be worth my talking to DMM.

Cheers

MichaelG.

.

Digressing somewhat: DMM's Absolute Encoder looks interesting.

 

Edited By Michael Gilligan on 26/05/2014 08:29:11

Edited By Michael Gilligan on 26/05/2014 08:37:52

[Les Jones 1Participant @lesjones1]

Hi Michael,
I could of made use of one of those encoders around 1975 when I was using the Oscar series amateur radio satellites I needed an absolute rotary encoder for my automated antenna tracking system. This was before microcontrollers were available at affordable prices. I finished up making an 8 track optical grey code encoder which was about 6" diameter. The electronics consisted of about 100 74 series TTL and 4000 series CMOS ICs. The data was punched onto a 5 hole paper tape using a Creed75 teleprinter. A frame of data was read from the tape every minute and the antenna rotated and elevated to the new position. I still have the rotator part of this system which used the flywheel and starter pinion from a Mini engine as the final reduction gearing. The main bearing was the front wheel bearing also from a Mini.

Les.

[Michael GilliganParticipant @michaelgilligan61133]

Les,

That's dedication !!

My how things have changed in our lifetime.

MichaelG.

.

P.S.  Those interested in encoders should enjoy this

Edited By Michael Gilligan on 26/05/2014 11:07:12

[Les Jones 1Participant @lesjones1]

Hi All,
Michael has pointed out that I have used the wrong spelling of "Gray code" (I had written "grey code" – apart from the wrong spelling I should have used a capital letter as it is named after a person.) The correct spelling will also make it easier to find a description of it on the web.

Les.

[Michael GilliganParticipant @michaelgilligan61133]

Thanks, Les

I'm sure that Frank Gray will smile upon you.

MichaelG.

.

… this is a useful start page [which is linked on the one I posted earlier]

[Neil WyattModerator @neilwyatt]

That sounds brilliant Les. I was chuffed with the 4-bit opto encoder for my wind direction indicator. A slightly less ambitious project

Neil

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