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System recommendation for newbie
« on: November 04, 2019, 01:09:35 AM »
Hello, I am new to CNC.
 I have a CNC3040 mini-CNC 3 axis engraver with faulty controller that needs replacing. The manufacturer wants a lot of money for it.
I have an old HP Compaq dc7700 low profile desktop computer, 2 GHz CPU and 4GB RAM  with a Windows 7 32 bit system. This PC has a parallel port, USB 2.0 and Ethernet ports. It also has a separate Radeon 6450 video card with 1GB memory.

Can anyone please suggest the best configuration of hardware and software to get this system up and running ?  My preference is to run Mach 4 software if you agree that is the best way to go
« Last Edit: November 04, 2019, 01:12:23 AM by JoeS01 »
Re: System recommendation for newbie
« Reply #1 on: November 04, 2019, 01:37:49 AM »
before think about mach  ,be sure yours servo is not analog comand (if so then you need buy the very expensive hardware)
if its support step/dir there no problem to jump in mach 4
Re: System recommendation for newbie
« Reply #2 on: November 04, 2019, 03:33:04 AM »
Thanks KatzYaakov, how do I do that, please?
Re: System recommendation for newbie
« Reply #3 on: November 04, 2019, 04:27:26 AM »
I  have tested the 3 stepper motors. Firstly the 2 coils on each have the same resistance ( about 3 ohms). When connecting a LED across each of the windings, it flashes when I  turn the motor by hand. It does not turn smoothly, but rather in little steps.

 When I apply a 9 volt battery to each winding, it steps in one direction, depending on polarity,  and then locks until the polarity is reversed.

Does this indicate what type of servo it is?

Offline Tweakie.CNC

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Re: System recommendation for newbie
« Reply #4 on: November 04, 2019, 06:15:48 AM »
Hi JoeS01,

I think perhaps KatzYaakov has mistaken your CN3040 for a different machine.

You do not have Servo's, you have bipolar Stepper Motors.

Do you wish to replace your controller completely or just the parts that are broken ?
Could you perhaps post a couple of picture of the outside and inside of your existing controller ?

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: System recommendation for newbie
« Reply #5 on: November 04, 2019, 06:19:37 AM »
Hi,

Quote
Does this indicate what type of servo it is?

Your description of the measurements you have made and the testing you have done confirm the motor you have as
common garden variety stepper motors. They are not servos.

A servo is an electric motor, it could be a synchronous motor (aka an AC servo), it might be a brushed DC motor, or
it could be a variable reluctance motor, of which a stepper motor is a particular example, coupled and mounted
with an encoder/resolver to indicate angular position. A controller, be it Mach4 in combination with an analogue motion
controller like the Hicon or a dedicated servo drive will drive the motor in direction and speed such that it angular
position (encoder) is exactly the same as is commanded by the trajectory planner (Mach4).

The controller/drive is said to 'close the feedback loop' and it gives a very crisp and accurate response to commanded position.

A stepper motor and its associated drive just steps a certain number of steps in a given direction. If the load is such that it
'misses or can't make a step' then the controller has no way to detect that fact. Thus if a two phase (normal) step motor is
commanded to rotate one revolution by the application of 200 pulses but it makes only 198 steps because it didn't have
the torque to make those last two steps it will end up at 356.4 degrees not 360 degrees as intended. Because a stepper is
'open loop' this inaccuracy will not be corrected.

This might sound like a disaster, but really its not. Provided your steppers are adequately sized and you do not ask more of them
than they are capable they will never miss a step and be accurate all day long. This is how the majority of hobby CNCs work.

There are a number of Chinese manufacturers making 'closed loop steppers' by incorporating an encoder onto a stepper motor
and a smart stepper drive. They claim they are as good as servos.....they're bull*********ting, they are good but still not a patch
on a real feedback servo. They do a good job of selling to  hobby CNCers who are paranoid about losing steps.

What drivers, if any, do you have for your stepper motors?

If you don't have any the US company Gecko make superb and robust drivers, all their leading models are 80V capable.
They aren't cheap. Leadshine AM822s are 80V capable up to 8.2A and are more reasonably priced. In order to make your
stepper go fast use the highest voltage your driver can handle. The Gecko and Leadshine 80V drivers will make any stepper
sing.

Craig
My wife left with my best friend...
     and I miss him!
Re: System recommendation for newbie
« Reply #6 on: November 04, 2019, 07:09:09 AM »
Thank for taking the time to do these replies, I appreciate your effort sharing your knowledge.
I  was given a CNC3040 by a relative who bought it off someone who had given up getting this working. I  have never met the original owner. I  have never seen a CNC controller before.
I  checked the controller and found the 48V to the spindle was not on the output side of the bridge rectifier on the PW3618 circuit board. There was the correct voltage from the toroidal transformer.  I  could not find a replacement circuit board. The previous owner had bodgied it up, and tried to use parts of the controller, and parts of a remote controller  with 3 stepper motor drivers.
So I  had to start from scratch. I  thought the best way to go was to get a new control box to replace the existing one shown in the pictures found here: http://www.dasq.com.au/CNC/

i  found a Compaq dc7700 with an integrated parallel port and USB socket , and thought this might be able to be used to drive a new controller, but am uncertain as to which software to use ( Mach3 or Mach 4)   and what computer operating system and interfacing equipment was needed to interface to the controller.

That is where I  am at right now. any and all help is greatly apprecaited
« Last Edit: November 04, 2019, 07:11:28 AM by JoeS01 »

Offline Tweakie.CNC

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Re: System recommendation for newbie
« Reply #7 on: November 04, 2019, 07:46:19 AM »
Sorry to say but the Toroid may be the only re-usable item in that controller unless you have the electronic skills to fault find and replace the defective components.
 
I don’t know of any ‘Plug n Play’ or EZ replacement controllers they all require some knowledge and skills to connect and set-up. The cheap Chinese controllers / boards offer no customer support and quite often the just don’t work at all and so are best avoided.
Please take a look at the Gecko G540 and have a read of the support information available on their website – this will give you a good idea of what is required and the degree of complexity etc. https://www.geckodrive.com/g540-4-axis-digital-stepper-drive.html

There is much to learn but, as a hobby, the journey is great fun (some tears along the way) and the rewards are more than worth the effort.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: System recommendation for newbie
« Reply #8 on: November 04, 2019, 10:36:05 AM »
Hi,
Mach3 AND Mach4 both work well but all development of Mach3 ceased six years ago, as a consequence Mach3 must
be regarded as a 'sunset' product whereas Mach4 is current and developing and recommended for all new builds.

I echo Tweakie's recommendation for the Gecko G540. Its fairly simple and has the capacity of one (only) 'parallel ports
worth of IO' and is only 50V capable rather than 80V as I had previously recommended. It is a Gecko product however and is good
quality. You would never regret the $300 on quality at least.....you may wish later that you had held out for individual
drives and a breakout board/boards/motion controller with more IO.

Note that the G540 can be driven directly by a parallel port thereby avoiding the cost of a motion controller. There is a Mach4
ready parallel port driver called Darwin ($25 license fee applies) but the Mach3 parallel port driver is free. If cheap sounds good
to you then Mach3 and a parallel port is the way to go. Be aware that the parallel port absolutely requires a 32 bit OS
Windows7 or earlier and will not work with most laptops. Even some desktop PCs just don't make good Mach3 parallel port
machines. often without particular rhyme or reason.

Craig
My wife left with my best friend...
     and I miss him!
Re: System recommendation for newbie
« Reply #9 on: November 04, 2019, 03:38:00 PM »
Thanks joeaverage and Tweakie.CNC for your helpful replies.
JoeA nicely articulates why my preference is for Mach4. So with my old Compaq dc7700 computer with parallel port , USB and Ethernet sockets, what operating system do you suggest I install - Win 7 32 bit ?
I like the strong support here for Gecko G540. Do you connect each of the 3 stepper motors directly to it? And does it have a speed control for the spindle motor?
On the faulty Chinese CNC3040 controller that I have, the supply to the spindle motor is 48V DC at the output of the bridge rectifier, but it rotates  when tested with a small 9V battery, albeit slowly. So I am not sure what actually reaches the spindle motor after its speed control electronics.
« Last Edit: November 04, 2019, 03:40:26 PM by JoeS01 »