Newbie- Documentation about commands or protocol used by drives/parallel port

[oinquer]

Hello, been interested about CNC machines for 2 or 3 months and have been looking into information and understood that i need a drive and a breakout board to drive the motors and communicate with the computer respectively....however i haven't seen any info about the protocol or commands the parallel port send to the drive.

What i would like is to have a look at some documentation since i would like to develop some programs with PIC's....
is it feasible? i have done some extensive electronics which used serial port to communicate with computers and it would be nice to develop or at least try it.
Help me out here please.

[selimoztunc]

Hi there,

It's not space technology, really. Pins are either high or low referenced to ground, which means 1 or 0. There are no intricate communication standards here. You can take a look at http://www.pminmo.com/ as I did. If you're into PIC programming, you will find some good documented controllers there and by any means build one just for the fun of it. I have made my own controller at first, but later bought a 4-axis one.

[oinquer]

hmm getting it...
what i cant seem to understand is, if its either pin up or down...how does the computer knows the drill has reached its spot? is there any kind of answer from the drive?

looking at link you gave there seems to be some kind of answer.... will check the link thoroughly

[BobF]

Most of the machines you find here in DIY use stepper motors. They take step and direction instructions, and give no feedback. You have to take it on faith that they did what you want.

[analogman]

Servos will give feedback through encoders. Steppers wont (other than limit or home switches).

[ger21]

Originally Posted by analogman Servos will give feedback through encoders.

But most Step/direction servos only feedback to the drive, not the PC.

[selimoztunc]

What you are referring to is called a closed loop system. Even with a system driven by steppers, you can still use linear position encoders along the axes to get feedback. Not a cheap solution, though. I wonder if someone around the zone tried to build something along these lines?

[oinquer]

hmm understood...what im missing here is...how do you know that one step has been done so the computer can send another step to the stepper? stepper speed configurable in software?
cause lets say...stepper is at x=0 y=0 and needs to do a marking at x=20 y= 19 , how does software knows the stepper is at those coords already?

thanks for your time guyz

[selimoztunc]

Let's think that you have a 5 TPI (turns per inch) ballscrew driving the gantry directly coupled to the stepper. Your speed is configureable in software, so the software knows when the motor completes a full turn (usually 200 step, higher if your controller supports microstepping), the gantry will move 1/5 inches (25.4 / 5 = 5.08 mm. in metric units). Divide that number by 200 and you will find travel per step. There is no feedback in most DIY systems, so if you loose steps, your work is mostly gone.

[oinquer]

ok thats what i needed to know

Just ordered a new programmer last week, will look into this in a few days, maybe im actually able to do something.

Thanks for you time guyz

[analogman]

Originally Posted by ger21 But most Step/direction servos only feedback to the drive, not the PC.

Definitely. The difference here is he is planning on building his own drive with a PIC processor. Saves from him getting linear position encoders and combining with a stepper. It that is what he wants to do.

Oinquer - for your PIC, make sure you have lots of treatment for noise. Also if your processor handles any switches make sure to have debounce code. What language will you be using?

[analogman]

Do a google on "basic stamp stepper". LOTS of hits. It will give you some good tips from other peoples experience, even if you are using a PIC. Stamp Basic is easy to decipher and recode into the language of you choice.