I think I figured it out!

[chuckknigh]

Topic 1:

I think I figured it out! I've been obsessing over how to make sure that the electro-mechanical portion of the CNC router would be compatible. But, given the odd and random collection of parts that I've seen on this site, I couldn't figure out how to make a common interface that would control them all.

I think I've got it! You don't even try to make it "compatible."

You install a "driver" or some sort of a layer between the g-code interpreter, and the parallel port. It's calibrated to your actual equipment...probably number of steps per revolution, or some similar unit that would be common to all drive systems.

Then, you let the computer determine that to move 5 units, you send "so" many pulses to the controller module.

Is this how it actually works? It is a workable solution.

----------------------------------

Topic 2:

Motor specifications. Like I said, I've seen "random parts" mentioned on this forum, which leads me to believe that almost anything can work. But, if starting with a clean sheet of paper, what type of specs would be good for the stepper motors?

Is something like this good?
http://www.bgmicro.com/prodinfo.asp?...tepper&stype=3

48 steps per revolution, 1800g.cm. holding torque. The resolution seems rather low, but if it's driving a screw drive this may not be the case. The price is definitely right. And, is 1800g.cm. a high enough torque?

http://www.bgmicro.com/prodinfo.asp?...tepper&stype=3

This one has 1/3 the torque, but 100 steps per revolution, and it's bipolar. Would this be a better choice?

I'm literally trying to learn the basics, at this point. Building a stepper motor controller is not outside of my abilities -- my concern was with the software interface, and if my guess (above) is right, then I needn't be concerned any more.

Thanks!

-- Chuck Knight

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[kong]

I can't help you with your question, coz I'm a noob myself, but I've learnt a LOT by looking at what other guys have done. There's some good info on these sites if your interested:
HomeCNC
Sherline CNC
Drill conversion
Hope they help.
Oh yeah, and the first two are regulars around here, so don't be scared to ask them wuestions!

[balsaman]

Chuck,

- You worry too much. The Gcode interpreters do it all for you. They all have the ability to run all the popular setups. Here is what you need:

- Machine control software (gcode interpreter) such as TurboCNC, CNCpro, Mach 1 etc.
A bit of hardware called a driver or controller card. Stepperworld, Gecko, Xylotex etc. It interfaces with your parallel port, and wires go to your motors

- Motors (steppers)

The above mentioned software can easilly be configured for whatever you build, no matter what you use. You set it up for pulses per inch of travel, so it doesn't matter if you use 200 or 400 step per revolution motors, or if you use 3,5,8,10,20 or whatever pitch screws.

[Laff Riot]

Chuck - thank you for asking that question. For those of us that have not made thier own machine yet we have to keep plugging away at the answers until one day the lightbulb doesnt dim and we "GET" it. Unfortunately we forget to tell the others about the rough patches we have had on the ole learning curve.

I just assumed that I bought all the electronic / software parts carefully matched to tolerances set by either NASA engineers or people that build brains in their spare time, threw it all in a big box, sacrificed a couple goats while chanting in a smoke filled room and If I got it all JUST right my machine would work.

We need more posts like this - the things that the average person had problems understanding from the go - Maybe a whole thread dedicated to the "Art of the Duh!" question and answer.

Ty Chuck - you just de-mystified a large chunk of the puzzle for me.

[balsaman]

I should add...buy at least 200 step per rev motors, that way, you get decent resolution. For example, if you use 10 pitch screws, you will get theoretical accuracy of .0005" or half a thousands of an inch.

Bipolar motors need bipolar driver cards. (Eg. Xylotex) Unipolar motors can be wired unipolar or bipolar. Unipolar motors can be driven by an unipolar driver (eg. stepperworld FET3)

For a small to medium size home made router you should be looking at 60-100 oz motors. Mine is 12x24" and uses 100 oz. unipolor motors.

Eric

[chuckknigh]

- You worry too much.


It goes with the territory -- I'm an anal retentive tech geek who happens to also be an uber-perfectionist.

Is it any wonder that so few of my projects see their completion? :-)


- Machine control software (gcode interpreter) such as TurboCNC, CNCpro, Mach 1 etc.


That's the layer I was talking about. (It could have been implemented in software or hardware, really, and placed in half a dozen different places) Something that takes generic g-code and turns it into instructions specifically for your setup. So, I guessed right!


A bit of hardware called a driver or controller card. Stepperworld, Gecko, Xylotex etc. It interfaces with your parallel port, and wires go to your motors


Based on an LM298 chip, probably... (I think that number is right) It just says that if pin (x) on your parallel port goes high, advance by 1 step. That sort of thing? Or is it more complicated than that?

If it's really that simple, then I can build my own controller with very little trouble.

-- Chuck Knight

[chuckknigh]

Chuck - thank you for asking that question. For those of us that have not made thier own machine yet we have to keep plugging away at the answers until one day the lightbulb doesnt dim and we "GET" it. Unfortunately we forget to tell the others about the rough patches we have had on the ole learning curve.

Tell me about it -- usually the FAQ is written by someone who understands the subject rather well, but who barely remembers the FAQs he asked himself, when he was starting out.

Experts are all well and good...but they have to be able to communicate the basics to the newbies!

I wonder if this forum software has a facility to save threads like this? Append it to the FAQ, essentially.

I just assumed that I bought all the electronic / software parts carefully matched to tolerances set by either NASA engineers or people that build brains in their spare time, threw it all in a big box, sacrificed a couple goats while chanting in a smoke filled room and If I got it all JUST right my machine would work.

You forgot a few things.

First, the smoke filled room. The smoke must be released from electronics in a sacrificial ceremony called burn-in. The smoke has magical properties...it must! The circuits will not work without it.

Then, you forgot to spin around 3 times and blink left once, right once, and then both eyes once...one blink for each axis.

Oops...wait a second...that was the love spell from "I Dream of Jeannie." Sorry! ;-)

Ty Chuck - you just de-mystified a large chunk of the puzzle for me.

For both of us, actually...I've been obsessing over the interface and the compatibility layer. I knew from the get-go that I can build a machine, and make it work -- I just didn't want to have to write custom software to control only my machine. That would have been too much work for too little gain. I started coming up with ways that I would use if designing a more generic system, and it occurred to me. IOW the light bulb went on.

Glad I could be of some assistance.

-- Chuck Knight

[Laff Riot]

Wondering if anyone has made a rack and pinion machine like these.

http://www.aeronautauto.com/pages/plotters.html
-or-
http://www.carlsondesign.com/

Will the setup process be as simple as discussed above or are additional steps / equipment / software needed?

I plan to push dye markers around - a couple .oz each on the largest table possible for pattern making. I would be happy with tolerances as low as 1/8" so I hope I can get away with scaling down the setup to lower cost materials.

[balsaman]

Rack and pinion systems work ok but sometimes suffer from backlash. Also they need a gearbox on the motors. They can be very fast though.

Eric

[ToyMaker]

chuckknigh wrote:

Based on an LM298 chip, probably... (I think that number is right) It just says that if pin (x) on your parallel port goes high, advance by 1 step. That sort of thing? Or is it more complicated than that?

Most (all?) control software that outputs to the parallel port generates step and direction signals. By a happy coincidence, drivers that interface to the parallel port accept step/dir and turn them into motor drive.
I think the LM298 is a driver chip. It is used with the LM297 translator. The '297 takes step/dir from the p-port and turns them into phase signals. The '298 boosts the phase signals to motor power levels.

robotic regards,

Tom