View Full Version : parallel port with mach3, or USB with usbcnc?

Tue 11 May 2010, 08:41
Hi all,

i'm back with an other question!

If I'm not mistaking, you guys all use Mach 3? I've also been working with Mach for quite a while now, (on smaller cnc mills with ball-screws), and it works just fine!
I never gave it much thought before, but doesnt mach3 limit you're output resolution? You may correct me if im wrong, but if you work with microsteps, arent you guys limited by the max. output frequentie that you can squeeze of the parallel port?
Since Mach 3 only works with a printer port, i went looking for something that works with USB. The thing i found was USBCNC.
If one would build a Mechmate with this USBCNC software, and interface, you could have a machine with up to 3 times the resolution? (or atleast it would run a bit smoother).

What do you guys think about this crazy theory? :confused: or am i just talking nonsens?
I really would like to know what you guys think about this one? Maybe there are even some users of USBCNC on this forum?

. . .

Gerald D
Tue 11 May 2010, 09:35
We use SmoothStepper with Mach3 on our machines. Do some searches to find out more.

Tue 11 May 2010, 18:01
I believe with a fast computer you can Push Mach3 to 100Khz, your UI might run a tad slow though.
I use EMC currently at 25Khz (I change once a while :)) and that is plenty fast for me, but I am not running any beld drives.

However, your main concern seems to be resolution. But don't get fooled by these microsteps, the name is a bit misleading. micro stepping is mainly used to let your stepper motor run more smooth at lower RPM's, it's not that you can really get 3600 precise steps (as in step, wait a second, step, wait a second). For example, a stepper motor with microstepping cannot stop at half a step, it will always stop at a full step.
Microstepping only happens when the motor runs, not when it stops!

In fact, many stepper motor controller switch automatically to full steps above certain speeds, and they switch back to microstepping at lower RPM's.

See : http://en.wikipedia.org/wiki/Stepper_motor#Microstepping

So, if you really need higher resolution, then beld-drives or gairheads is the way to go, but you must run at lower speeds anyways if you really meed to be that precies.
But for woodworking you don't need to be ultra precise anyways.

Gerald D
Tue 11 May 2010, 23:30
Ries, see Can stepper motor be held in a "micro-stepped" position? (http://finance.groups.yahoo.com/group/geckodrive/message/18364)

I am still not comfortable with the answer from Mariss and I will do a test one day when I have nothing better to do.

Wed 12 May 2010, 07:11
pure theoretically it can be done but it would not be precise unless you put the stepper motor in a closed feedback loop back to the controller, much like how servo motor operate.

Marris is right however at some points and I was partially wrong in my above statement.
It still puzzles me why my Gecko drives are not running very hot when it stops. After all, if I stop at a microstep position, and I assume I want to hold my position like my Z axis I need to push 'some' current through the motor. simply said, if I step and the motor needs let's say 2A to keep that half microstep, then my geckdrive needs to some dissipate the other part of the heat (sinusoidal signal)

This (http://www.micromo.com/n391003/n.html) was a nice read and it explains what Marris was trying to explain in many odd words.

This is a quote from the bottom:

In summary, although Microstepping gives the designer more resolution, improved accuracy is not realized. Reduction in mechanical and electromagnetically induced noise is, however, a real benefit. The mechanical transmission of torque will also be much gentler as will a reduction in resonance problems. This gives better confidence in maintaining synchronization of the open loop system and less wear and tear on the mechanical transmission system.

In fact, taking an infinite number of microsteps per full step results in two-phase synchronous permanent magnet ac motor operation, with speed a function of the frequency of the ac power supply. The rotor will lag behind the rotating magnetic field until sufficient torque is generated to accommodate the load.


Wed 12 May 2010, 22:50
If I'm selling the microstepping, I WILL advertise on the improve resolution during motion & bury the holding position resolution performance in the darkest deepest dungeon I can find... or act dump when asked upon... I share the same doubt over the ability of the stepper motors to hold microstep position accurately without other short fall.

Gerald D
Thu 13 May 2010, 02:10
I imagine it is similar to suspending 2 magnets on 2 pieces of string (pendulums) and then getting them to hang a precise distance apart? :D

Thu 13 May 2010, 03:03
don't forget the fans that are blowing full blast from every imaginable directions ;)

Thu 13 May 2010, 06:52
I am not english speaking,

but that's why they say it improves resolution, but not accuracy.

@Gerald, I understand your analogy, but.. if you have such a rotational item and only one coil is energized, then the motor would be on a full step stopped.
However, if you start energizing one coil at 10%, and the other coil at 90%, then it theory you pull the rotor a little bit of it's full position, this generating a microstep.
The problem is that you don't know well how much the rotor was moved, just 'that' it was moved. The link I send explain this quite well and thus they say it improves resolution, but not accuracy.

Back to the answer of newbie.
Yes, micro-stepping does improve resolution, but not accuracy.

How are the two terms defined:
Resolution: The number of steps the system can do in a full turn.
Accuracy: How much the actual position of the rotor is different then then step number given.

On the IRC EMC channel they say that with stepper motors you always need to calculate with full steps to find the accuracy of a machine, these people usually know what they are talking about (I am just parroting :) )

Sun 16 May 2010, 03:39
Mach3 wich will make use of a parallel port (without Smoothstepper), and USBCNC hardware + software.

If all goes well, my cnc will be up and running within the next 2-3 months!! I'll keep you guys posted. But USBCNC looks very promising :)
USBCNC will not improve the accuracy, but maybe things will even run smoother then mach3? Also the screens of USBCNC look a lot better!

Lets see shall we. . . .

Sun 16 May 2010, 03:42
thanks for the replies all!!

If the mechanical part of my cnc is finished, i'm going to test the difference between Mach3 wich will make use of a parallel port (without Smoothstepper), and USBCNC hardware + software.

If all goes well, my cnc will be up and running within the next 2-3 months!! I'll keep you guys posted. But USBCNC looks very promising :)
USBCNC will not improve the accuracy, but maybe things will even run smoother then mach3? Also the screens of USBCNC look a lot better!

Lets see shall we. . . .

sorry for the last post:o didnt copy all of the text from google translate into the box :D

Sun 17 October 2010, 10:14
well, im back. . .

i am testing usbcnc as we speak, and it works fantastic!:eek::eek:
I like the "look" of the program the most.
MACH3 works great to, but if you get used to working with USBCNC, you dont want anything else!!
Its has got a very nice looking users inerface, and does anything mach3 can!

You can download the software for free at: http://www.edingcnc.com/index.php?pagina=7_download , or just look at www.usbcnc.com
Just give it a go, and you will tell me I am right! :eek:
(Also the manual can be found here)
Do notice, that you can only simulate things, an test the software if you dont have the usbcnc print connected to youre PC.

Currently i'm running the usbcnc interface card with the gecko 203V drivers, and it can't work any better.
It also has got really large icons, so if i decide to use a touchscreen in the future, i can :D

I have run into 1 downside thow, the usbcnc interface card can only put out a PWM signal to control the VFD, so i will have to use an extra small print to convert the PWM, to a 0 - 10V signal. BUT OTHER THEN THAT? ! . .

just download and install the software, and tell the other people and me, what you think here.

looking forward to some first reactions.


Fri 22 October 2010, 09:56
so? has anybody tried the software allready? I would really like to see some first reactions.