Thread: Another chinese CNC router

Yes, they can be adjusted. Just slacken them off, move the carriage a bit and then do them up again.

easy test you might have overlooked...

Check the continuity from the dirve connector to the motors. you should see a couple of ohms across each phase of the stepper and open circuit between them... stepper just vibrating sounds like a missing phase to me.

Good luck

Originally Posted by mhasting2004

easy test you might have overlooked...

Check the continuity from the dirve connector to the motors. you should see a couple of ohms across each phase of the stepper and open circuit between them... stepper just vibrating sounds like a missing phase to me.

Good luck

While I haven't directly tested the windings this way, swapping the X and Y axis to the Z axis drive, would have accomplished the same thing, I have checked the wiring between the driver board connector and the socket on the back of the controller.

Next step is to hook up the G540 and test with that,

I think a lot of it also has to do with the price range of the chinese machine you purchase, for 1-2000 dollars there not to bad, yes needs some work, I remember my first one I built easily 4k.

However when you enter the more expensive ones, 30-50k, you are hard pressed to fault the machine

Originally Posted by simso

I think a lot of it also has to do with the price range of the chinese machine you purchase, for 1-2000 dollars there not to bad, yes needs some work, I remember my first one I built easily 4k.

However when you enter the more expensive ones, 30-50k, you are hard pressed to fault the machine

You're right about the price range. As rodm said a while back, he'd be hard pressed to got the basic components for the price I paid.
I think mechanically it's OK and I'm fortunate enough to have the spare bits to make a new controller.
I'm going to order Homann a power supply and a few other shiny bits from (if I can convince his website to send me my password .) so I can try it out as a G540 based machine.

I've metered out the cables and' despite some differences in colour coding, it seems OK.

The output from the driver board, labelled A and A+ goes to one winding on the motor and B and B+ goes to the other. I'm not sure if the phasing is correct - I'm assuming it matters bbut I'm not sure what the symptoms would be if it were not correct.

You should be OK and worst that can happen is the motor runs backwards - easy fixed with software. If you have the phases mixed then it probably will blow the driver board. I'm referring to a four wire stepper here as six and eight wire steppers are something else again.

Steppers are 4 wire.

If one winding is connected to (say) A and A+ and the other to B+ and B (as opposed to B and B+ i.e. backwards) , wouldn't this cause the motor to oscillate as one winding is trying to move it in one direction and the other, the opposite direction?

Being the first to admit to my limited knowledge unless somebody chims in and corrects me it will still work.
I just match the pairs and connect them after that fixing the direction in the software. Considering the number of motors I have connected the law of average is that I would have mixed the poles at some stage.




So I don't give you a bum steer here is an extract of a post by Ken (sawdustsniffer) responding to the same question.
I suggest he is correct and ignore all offerings from me.


blind wiring up of steppers can have 4 results , as long as you find the "Pairs " first
if A+ ,A- , B+ , B- is correct ,
A- ,A+ . B - B+ , will make the steeper run backwards
A+ , A- , B- B+ , will make the stepper "Hum " and not move at all
A- A+ , B+ B- , will hum as well, as the coils fight each other ,
if you mix up your "pairs " it wont work at all
if your motor "hums " and dosnt move , swap 1 "Pair" around , 50 , 50 chance of getting it right , at worst is will go backwards ( software correction is fine )

Thanks Rod, that covers some of the symptoms I'm seeing.

The connectors are not going to stand up to much pulling apart and moving of pins, or re-soldering in the case of the round 4 pin connectors, so I might take the opportunity to replace the connectors on the motors with something a little more durable/reliable.

What connectors do you use at the motor? The motor leads are quite short so I only want to do this once!

I solder and heatshrink the wires. No connectors to go wrong.

I think what Ken has described is if you are running unipolar (ie 6 or 8 leads) not bipolar (4 leads). The only thing that will be affected with swapped A+A- or B+B- is the direction... just don't do AB !!! then your magic smoke will escape.

The best way to think of stepper motors IMO is as 2 relays and not your classic rotating field motor. Energize one coil and it holds one position when the next coils is activated it will pull or push the rotor to the next postion be it CW or CCW depending on the phase of that coil. Because the drives alternate pushing and pulling of both phases (hence the term bipolar... not a description of its mental state... although sometime I would think otherwise) if it does not get "grabbed" by the alternate phase (ie open circuit on on phase) the motor will vibrate back and forth as its undecided which way to go. If you manually give it a spin in either direction it will chug along in that direction but only on one cylinder so to speak.

If on the other hand you have sufficent drag on the motor such that the rotor lags enough to be overtaken by the rotating field it will also oscilate and that can happen at resonance speeds where the motor "stalls" due to lack of torque.

Start with very conservative (ie slow) speed and acceleration settings and ramp them up to find the sweet spot on you machine.

Cheers

After a bit of proper testing i.e I wrote down the results , I've confirmed that the Y axis driver is at fault. I might order a new driver board from the carving-cnc.com site I mentioned te other day but with $45 shipping, I'd want to get more than one. If there is anyone who needs/wants a spare driver, let me know as if we can split shipping it may make it worth while.
Perhaps I should just get the 4th axis as the cost of including the driver would be minimal - although the thought of a couple of kgs of metal packed together with a circuit board doesn't fill me with confidence.

I'll go ahead and build a G540 based controller as all I need for that is a suitable case and a power supply which I should be able to get even in Hobart

Originally Posted by snowyskiesau

I'll go ahead and build a G540 based controller as all I need for that is a suitable case and a power supply which I should be able to get even in Hobart

Can you use a G250?, should be simple, you'd just need to find some room for it or make a small seperate enclosure, would save wasting so much on shipping.

For the case nothing beats the enclosure from jaycar, homann also sells this one.

Professional Bench Enclosure 88x279x304mm - Jaycar Electronics