Stepper Motor Cable Length

[G WalkerParticipant @gwalker75501]

I have followed Tony Jeffree’s MEW articles, and built a 4 axes stepper motor drive unit. The plan is to fit CNC first to a lathe, and then eventually a mill. The drive unit is housed back to back with a desk top PC in an enclosed MDF box, to give some protection from coolant spray and dust. (A fan provides ventilation.)

 

The unit has worked perfectly in a small test rig. However, on the bench a basic problem has occured; the unit is not a good fit between the lathe and mill! This means that instead of having the unit central with cables 1 – 1.5m long, the unit must be placed to one side requiring some cables 3m long.

 

I have spent a little time searching the web looking for comment on CNC cable problems. In summary, most problems were concerned with not using shielded cable for signal & power cables, and not grounding the outer once at the drive unit end. I could not see any problems relating to cable length. (Do the adjectives shielded, screened, shrouded & sheathed all mean the same thing?)

 

Tony Jeffree’s design uses shielded cable. For signal cable I have used screened audio cable from Maplin. The power cable is RS 4 core shrouded, 16 x 0.2mm. The largest stepper motor is an ArcEuro 220Ncm rated 2.5A/phase.

 

I would appreciate any comments about problems that are likely to occur if I use 3m power cables.

 

Thank you

 

George W

[G WalkerParticipant @gwalker75501]

[John Stevenson 1Participant @johnstevenson1]

None at all, I have used stepper motor cables far longer than that with no problem and unshielded as well.

 

Now logic cables can give problems, a recent retrofit with 6′ of cable from the breakout board to spindle motor board created a lot of problems in voltage dropping which turned out to be a breakout board problem.

 

John S.

[G WalkerParticipant @gwalker75501]

John

 

Thank you for your response. It helps settle a niggling doubt in my mind.

 

After reading your reply, and giving it two seconds thought, it is now obvious that the sizes of the beds & tables used in some Mach 3 router & plasma cutter CNC configurations are larger than the typical model engineering lathe & mill dimensions. I have never read of special action to cope with the longer cables used in such set ups.

 

Thank you again.

 

George W

 

[john swift 1Participant @johnswift1]

 

1, screened cable connecting the stepper motors will reduce the electrical noise radiated from the cables

I would not expect problems with long cables as long as voltdrop is not excessive

you need to look at the resistance / metre for the cable

unless the steppers are insulated from earth ,only connect at the driver end

 

2, pickup of electrical noise on the cable connecting the pc to the breakout board

and breakout board to the stepper driver is the problem

with the printerport working at TTL levels

valid inputs are – logic 0 is between 0v and 0.8v , logic 1 is between 2v and 5v

valid outputs are – logic 0 is between 0v and 0.5v , logic 1 is between 2.7v and 5v

it is easy to pickup stray input signals that are at the undefind levels between 0.8v and 2v

(more than a logic 0, but less than logic 1 levels ! )

valid logic 1 levels are also possible !

the capacitance of long sceened signal cables will round off the step and direction

signals causing lost pulses and timing errors

very often screens are only connected at one end to avoid earth loops

screened cables can have one screen around all the wires

or each wire individualy screened

the high quality scart leads have a combination

the video and audio being individual screened cables enclosed with un-screened wires

with in an overall screen

 

John

 

Edited By john swift 1 on 04/09/2011 20:21:37

[jason udallParticipant @jasonudall57142]

Hi all.
I have been given some steppers and am looking into a home brew cnc.
So far so good
Heres the spec.
IFS 61/2CAN-DA1/-I-Z30/O-001RPP30/I12
phew… Ok looks like can bus 45Nm 36V

Real question .do any of the free/ low cost cnc software able to drive via CAN ?

[jason udallParticipant @jasonudall57142]

or should I strip em down to just the motors..same 20,000 steps/ rev looks tasty…

[Ian PParticipant @ianp]

Jason

 

What do these motors look like? what make are they?

 

20,000 steps is an awful lot for a stepper motor, I dont think I’ve ever heard of that before.

 

Maybe it has an encoder with that resolution, but to me they sound like servo motors.

 

Are you saynig the motor has built in electronics that takes a CAN bus signal?

 

Ian P

[jason udallParticipant @jasonudall57142]

yeah
the ifs is intelligent …ie all motor drive is built into box on end of motor…probably realy servo that “acts” like stepper…
Cant get piccy up but motor is about 3″ cube with about the same of drive electronics bolted on.. Looks like encoder embeded in there too but manual does talk about 20k steps/rev.
Also has 8bit i/o built into box.
Now maybe config able to act dum with simple two input STEP & CW/CCW

[jason udallParticipant @jasonudall57142]

manual also talks of “3 phase stepper” which is new to me.

[Ian PParticipant @ianp]

Jason

 

Your motors are superb, but making use of them might not be plain sailing!

 

The manufacturers of servo motors and drives are generally not helpful to individuals, data is hard to get hold of and frequently you need to buy their software just to configure them.

 

I have a beautifully made servo drive unit which I bought on eBay. The manufacturers want £900 to swap the input module (a tiny PCB)! and configure the drive to suit the model of motor I have.

 

If you can find some way of making them work with easily available NC software I will be impressed. I have a USB to canbus adapter, trouble is there are lots of different Canbus standards and you need to be conversant with programming to make any sort of progress. I don’t want to pour cold water on your ideas but I imagine it will be tough going.

 

Ian

[jason udallParticipant @jasonudall57142]

thanks…Canbus not too hard but looks like CNC side dead in water

dont fancy reinventing that wheel….still if I can get the config tool or at least a terminal progamme to talk to them making them emulate steppers ought to be possible…

hanks again

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