servo control vs stepper control

[Peter.]

I've been gathering parts to build a CNC milling machine capable of milling aluminium and steel. I have the base of a warco round-column mill to which I'm going to mount a very robust 6" square column and figure on using a heavy linear rail arrangement to carry the head, which I'm going to make myself.

I have some redundant axis control hardware coming - not sure what just yet - I got a call from a friend who is stripping it out of a machine for me.

I already have this hardware, which I'm told is a servo motor with a driver that can use step-and-direction inputs.



The stuff I'm told I have coming is similar motor type but with servo drivers and encoders. What I'm not clear about is how, or even whether, it's prudent to combine the two different types of drive/motor combinations in one installation, what the pitfalls might be and whether a program like Mach3 can even deal with encoder-resolved steppers, and if not, what my software options are.

You can gather that I'm awfully green in the world of CNC. I'm not daunted but I'd appreciate some direction from those in the know.

Pete.

[JAZZCNC]

What I'm not clear about is how, or even whether, it's prudent to combine the two different types of drive/motor combinations in one installation, what the pitfalls might be and whether a program like Mach3 can even deal with encoder-resolved steppers, and if not, what my software options are.

Ok first yes it's fine to combine different motors on same machine, at worst it may mean having more than one PSU if they are so different.

Regards Mach3 then it can read the encoders to display position but it can't do anything with them.? By that I mean it can't command the servo to go back or forward if it runs out of position.
Mach sends out pulses to the servo drive and just takes it on faith it's happened and got to position, it doesn't check if it's actually got there or not.
With "normal" stepper drives that's the end of it and if it runs out of position you'll never know untill it shows in the work.

Now with servos the Drive can read the encoders and check it's within an acceptable error tolerance and if it falls out of that tolerance then it will fault the drive, which can send a signal back to mach which then e-stops the software. But again the Servo drive can't command Mach to move if out of position only report that it is.!!

Not sure but I think Linux cnc can talk to the servo's but I don't know anything about it so can't help here.!

Now here's where it's starting to get interesting regards the new digital stepper drives, some have a built in step error and can fault if fallout of tolerance sending a signal to Mach3 or any control software so working just like servo drive in this respect. . . . BUT . . . Here's where it's really starting to get very very good in the digital stepper world.?
The new Lead shine drives have positional error detection built into them and won't let the stepper run out of position.? By that I mean they correct positional error internally in the drive so don't need the Drive and control software to talk to each other.!!
They take the commanded position and make sure it gets there and if it goes to far they move it back or vise versa. Affectively you can't lose steps because the drive corrects any error and makes sure it arrives safely at the intended destination.

I'm currently playing with one at the minute and can tell you they are an amazing leap forward in stepper technology that will drive the price of servos down and in some cases thru there ease of use replace them all together.

Anyway I digress.!! Yes you can use mixed motors and yes Mach will work with them like said above.

One thing about that drive I've seen thou is it says 24V signal.? I'm sure that refers to the signal it expects to receive and the parallel port works on 5V.
It's common in professional industrial machine controls to use 24V signals so I suspect you won't be able to use that drive unless you find a breakout board that can change the signal from 5V to 24V.? I don't know of any.?

Hope this helps.

[boldford]

. . . . . I suspect you won't be able to use that drive unless you find a breakout board that can change the signal from 5V to 24V.? I don't know of any.?

Hope this helps.

As these BoBs breakout board | eBay have complete isolation betwixt I/P and O/P and are fitted with nothing other than EL817s I would think they could be used for the 5v to 24v translation.

[Peter.]

Thanks Jazz & Boldford. Seems i have the choice of either similar to the similar unit to above or smaller 0.34Kw Berger Lahr motors, or itsubishi motor with J2s-40A drive, which on doing some quick research seems like it might accept 5v signals anyway.

Please tell me, aside from the drive controllers and breakout board, what other fundamental hardware am I looking for?

[JAZZCNC]

Please tell me, aside from the drive controllers and breakout board, what other fundamental hardware am I looking for?

Presume you mean electrical hardware.? If so then Nothing really other than PSU(s).

[boldford]

Presume you mean electrical hardware.? If so then Nothing really other than PSU(s).

Stating the obvious; a PC running Mach3 or LinuxCNC would be useful too.

[Peter.]

Psu for the drives? The one I have is mains powered, so just a 5v for the breakout?
Pc is no problem, but linux is alien stuff to me.

[boldford]

Psu for the drives? The one I have is mains powered, so just a 5v for the breakout?
Pc is no problem, but linux is alien stuff to me.

The BoB draws such a tiny current you can tap off a spare HDD (or similar) connector inside the PC.

[JAZZCNC]

The BoB draws such a tiny current you can tap off a spare HDD (or similar) connector inside the PC.

I wouldn't take that route.? The drives are industrial grade and servo's are powerful beast's that unlike steppers tend not to stall when the shit hits the fan.!
For this reason things like limit switch's and E-stops become very important with servo's. They are sensitive to electrical noise and for this reason I wouldn't run any e-stop or limit switch's with 5V, instead using 24V which is more industry standard. So you'll need a 24V PSU so then I'd run the BOB from that, most decent bob's will run off 24V.

[boldford]

I wouldn't take that route.? The drives are industrial grade and servo's are powerful beast's that unlike steppers tend not to stall when the shit hits the fan.!
For this reason things like limit switch's and E-stops become very important with servo's. They are sensitive to electrical noise and for this reason I wouldn't run any e-stop or limit switch's with 5V, instead using 24V which is more industry standard. So you'll need a 24V PSU so then I'd run the BOB from that, most decent bob's will run off 24V.

I wasn't suggesting he drive the CNC M/C side of the BoB from the PC. Only the PC side of the optos would come from the HDD 5v. I'm sure your PC wouldn't want you to put 24v or more up its paraport. As I stated the EL817s provide the isolation; on this BoB inbound and outbound, so your e-stop and limits etc. can go up to, say, 30v.