Got a stepper and drive - but how much use is it to me?

[Pete.]

A friend of mine promised to keep an eye out for any stepper motor stuff for me, and came up with this. I know it's good quality industrial stuff, and I can get a bit of tech help off him if I can use it, but I'd in the dark about it's suitability for my home use being a CNC novice and all. I have a mind to use it for a Z-axis drive on a CNC mill project, I figure I can use this and perhaps a lighter duty setup for X and Y.

So, can anyone tell me - can I easily use this stuff? Apparently the drive has settings for 1000 and 10000 steps per revolution.

[9fingers]

As another CNC newbie, I've been trying to decide how much I can help you without saying "it depends"
But it sort of does depend on the machine size.

4Nm is plenty for X & Y on most hobby machines. Unless you are trying to make a fast machine, it could be geared down for machines at the larger end of the hobby market.

Z axis application will depend of whether you are going to fit a ballscrew or use the standard acme screw that the machine possibly has at the moment.
I am playing with a knee mill at the moment where the knee weighs about 100kg. As belt and braces I've just fitted a 12Nm motor and been told by other who know far more than me, that it is too big, will be slow and a bigger machine than mine behaves ok with 7Nm (not sure if that has a Ballscrew or not)

All I can really suggest is either wait for a more expert answer or rig it up and see how it behaves.

Erm, have I helped? Not sure so I'll go back under my stone and see what others have to say.

Bob

[Rob.Wilson]

Hi Pete

Looks like a servo motor ,,,,,,  ,,,,,,, i am probably wrong 


Rob

[Pete.]

Pretty sure it's a stepper, but my buddy said he thought it could act as either, or the drive could run either, or something...

Does the attached pdf shed any light? From what I can gather it'll take normal step & direction except it runs on higher voltage.

[Rob.Wilson]

Were be the PDF Pete ? 


Rob

Edit , slap me stupid , i found it 

[Noitoen]

That is a servo motor that can act as a stepper. There is an encoder at the back that acts together with the drive and usually more accurate than the stepper because once you give the order to move in amount of steps, it will do so and complain by giving an error information if unable to comply, unlike stepper who will skip steps without the controller knowing.

[Pete.]

Mine has no encoder - but the drive has a facility for one as an option. Will I encounter any problems with the 24v signal votage requirement?

[John Swift]

Hi Pete ,

to use the stepper drivers you will need to either convert the 5V TTL logic signals from your breakout board / printerport
to 24v levels as  used by industrial   controllers

or modify the stepper drivers to the 5v input version by changing a few resistors


to avoid modding the stepper drivers
you will need to use either a TTL logic IC with a open collector output like the 7407 or transistor array like the ULN2803
http://www.cedmagic.com/tech-info/data/7407.pdf
http://www.datasheetcatalog.org/datasheets/90/366828_DS.pdf

of the two IC's,  the ULN2803 will be the easiest use on a piece of veroboard (perf board)
as all the inputs are on one side  and the outputs on the other

with a +24V supply connected to the drivers + step ,+dir and +enable inputs
 using a  ULN2803  ,the +5V TTL logic outputs from your breakout board  will  be able to switch the drivers - step , -dir and  -enable inputs to ground

when a breakout board output is at 0v the ULN2803 output will be switched off and no current will flow through the LED in the stepper drivers input optoisolator


it will be possible to modify your drivers if you had the circuit diagram or traced the connection to the optoisolators
for each input you will need to change the resistors that limit the LED current
for 5V inputs the resistor will be  about 220 to 330 ohms

    John

[Pete.]

Thanks John, for that comprehensive reply. At least I know I can make use of this stuff, so now it's onwards to find some motors and drivers for the X and Y.

[Pete.]

Bit of a follow-up here. I've managed to get a second similar unit, and I've found this breakout board which supports 24v outputs. Am I right in thinking that this is all I need for an interface between my parallel port and the drives?

http://www.cnc4pc.com/Store/osc/product_info.php?cPath=33&products_id=245

[John Swift]

Hi Pete ,

I've just had a look at  page 4 of the  breakout boards manual  and while it looks like it will work
I expect connecting together the opto-isolaters in both the breakout board and stepper driver
will limit the rate at which  you can step the motors

you should be able to test the stepper drivers with the C31 board
but you need  a breakout board without opto-isolators on the step and direction 24V outputs

   John

[Pete.]

Life's never easy is it

I think I'll get that board, I have some servo drives coming that also need 24V signals and it should com ein handy for that too.

Why does doubling-up on the opto-isolators cause this slowdown John? I'd reason that if one set could handle the rate then two in series should be able to also?

[John Swift]

Hi Pete ,

compared to the switching speed of the printer port and the stepper driver circuits
the photo transistor in opto-isolators are a bit slow switching off

with an opto-isolator on the breakout board and the stepper driver the step and direction the switching speed is reduced twice !

high speeds transistors  have small base collector junctions to minimise the base collector capacitance you have to discharge when you switch off the transistor
( the miller effect makes the base collector capacitance appear to be even larger)

 opto-isolators  photo transistors have a large base collector junction to be more sensitive to the LED's light

    John

[Pete.]

Aah, I understand now, the time it takes to process the signals is a cumulative delay to the system. Thanks for the explanation John.

I'll take a look about to see if someone does a non-isolated breakout board, otherwise I guess I could just wire the parallel lead wires direct to the axes via one of those converter chips.

[John Swift]

 
Hi Pete ,

so far I've not been able to find a breakout board which is able to switch the 24V signals for  your stepper driver inputs that don' t use an opto-isolstor
may be you will have better luck

   John

[philf]

Pete, John,

I am using opto isolated drivers and an opto isolated breakout board and haven't seen a problem. I don't know how fast you want to your machine to travel but my mill is set to 4,000mm/min maximum with 5mm pitch ballscrews directly driven from steppers. The drivers are set to 1/8 microstepping so, by my reckoning, at 4,000mm/min my motors are being fed with 21,333 steps/second.

I know that 4,000 mm/min isn't that fast when compared to commercial CNC machines but it's fast enough that you can't hit the emergency stop quick enough when something is going wrong - e.g. when not setting a safe z height large enough to clear a socket screw clamping the part to a fixture. They don't machine too well at a 4,000mm/min feed! 

Cheers.

Phil.

[Pete.]

Hi Pete ,

to use the stepper drivers you will need to either convert the 5V TTL logic signals from your breakout board / printerport
to 24v levels as  used by industrial   controllers

or modify the stepper drivers to the 5v input version by changing a few resistors


to avoid modding the stepper drivers
you will need to use either a TTL logic IC with a open collector output like the 7407 or transistor array like the ULN2803
http://www.cedmagic.com/tech-info/data/7407.pdf
http://www.datasheetcatalog.org/datasheets/90/366828_DS.pdf

of the two IC's,  the ULN2803 will be the easiest use on a piece of veroboard (perf board)
as all the inputs are on one side  and the outputs on the other

with a +24V supply connected to the drivers + step ,+dir and +enable inputs
 using a  ULN2803  ,the +5V TTL logic outputs from your breakout board  will  be able to switch the drivers - step , -dir and  -enable inputs to ground

when a breakout board output is at 0v the ULN2803 output will be switched off and no current will flow through the LED in the stepper drivers input optoisolator


it will be possible to modify your drivers if you had the circuit diagram or traced the connection to the optoisolators
for each input you will need to change the resistors that limit the LED current
for 5V inputs the resistor will be  about 220 to 330 ohms

    John

Hi John,

I've bought some of the ULN2803A chips, when they arrive I'll set about blowing them up

[John Swift]

Hi Pete ,

once you receive the ULN2803's you will have a choise,

if you find after tests   you find the C31 board is OK  and you don't need the ULN2803 IC's for the step and direction signals for the stepper drivers   
 you can use a ULN2803 to drive any  relays you use instead off the transistor in the 4N33 opto-isolator on the C31 board


used as a relay driver the ULN2803 needs the  8 cathodes  connected to  pin 10
will need to be connected to the relay positive supply (+50V max)

   John       

[Pete.]

Cheers John, something I've never thought about. I was lucky and found a nice enclosure today, inside were some DIN rails and a nice 24V supply, along with a 12V supply and some kind of programmable electronic relay block doo-dad called a Siemens Logo. I really only wanted the box for a housing but the stuff inside should come in useful too.

Is it safe to wire the parallel lead wires directly to the ULN2803?

[John Swift]

HI Pete ,

yes its safe to connect the ULN2803 input pin to the printer port output

the ULN2803 has an internal   2.7K resistor connecting the darlington transistor base to the input pin
this limits the current that can flow from the printer port , into the IC input and then to the printerport ground -
the IC commmon 0V pin 9 is connected to the printer port ground pins 18-25 and the -24V power supply terminal   


if you look at the data sheet for the ULN2801 to ULN 2804   IC's
you will see they all have 8 darlington transistors with a minimum current gain of 1000
 the difference being the components connecting the input pin to the base of the transistor

the first transistor that makes up the darlington transistor provides most of the current gain and the second low gain transistor can switch a current of 0.5 A at 50V
this in effect gives you a high gain power transistor but with a base emitter voltage of 1.2V instead of the usual 0.6V for a silicon transistor

with  a  +3.3V logic 1 out of the printer port
the current into the IC will be 2.1V/ 2700 ohms = 0.78 mA
or with a +5V logic level  3.8V/2700 = 1.4 mA 

  John

[Pete.]

John, I don't know where I would be without your help. When the IC's arrive I'm going hammer one into a vero board and see if I can get this drive to respond. Thanks again.

I just looked up what the Logo is, and it's a PLC ladder-controller with an expansion block. Go no use for it that I can think of so if it's any use to you, you can have it.

[Pete.]

I've now got my Darlington IC mounted in a test board, and I want to wire it up to a parrallel port cable. I figure the IC needs a 5v supply which I'm going to have to run from the PC power. If I just want to control a single drive, just for testing, is it a matter of powering the IC, configuring one axis in Mach3's ports & pins to two pins and running those two pins through two inputs on the IC then taking the corresponding outputs to the drive? Is it that simple?

[John Swift]

Hi Pete ,

you don't need to connect a 5V supply to the ULN2803
but if your printer port output  is low   you may need to connect pull up resistors
from +5V and the outputs


    John

[Pete.]

Thanks John, I had come up with this, obviously electronics is a weak subject for me. Can you give me a quick appraisal so I know where I went wrong.

[John Swift]

Hi Pete ,

just move the -24V supply from the IC pin 10 to pin 9

you need to connect the negative 24V supply terminal to the printer port ground ( pins 18 to 25) and the ULN2803 pin 9 - the common connection to the eight transistor emitters and not to pin 10 .
in this application you don't need to connect pin 10

pin 10 is connected to the the cathode of eight diodes that are normally connected to the positive supply for inductive loads like relays and motor coils
 
the diodes protect the transistors from the back EMF when the transistor switches off

     John

[Pete.]

And the news is - it works like a BEAUTY! I soldered it onto a piece of veroboard and off it went first time, no pull-ups required.

What can I say John - thank you so much for your help with the circuitry. Long way to go yet but I feel I've leapt a giant hurdle just getting one motor to respond to the jog key.

[John Swift]

Hi Pete ,

I'm glad I've been able help

 now have you been able to jog the motor

1) you have proved your PC's printor port is working OK
2) mach 3 or what ever software your using is set up correctly
3) and the stepper drivers are working
4) the ULN2803 adaptor is wired correctly
 
thats a great success in my book 


    john