[runinbymdnt]

I am building a large all metal cnc router table. I have both brushless and brushed motors in stock that I can choose to use. I like the brushless but both have the power to do what I need them to do.

Neither have encoders, both have 50 amp 24-48v dc controlers.

The use will be light industrial, not hobby.

Can you, been there done that, machine builders help me decide what to use? and more importantly, why?

Thanks
JK

[Karl_T]

The only issue I'm aware of is brush wear. Important on a machine that runs 24 - 7. Brushless can be far more expensive. As you already own them, I guess cost is not the issue.

Karl

[daedalus]

Brush servos are usually cheaper, but suffer from brush wear and increased em noise (due to arcing with brush contacts). Brushless are great for running life and noise, but require more complex commutation electronics, so the drives are usually more expensive.

One thing to consider with brushless dc is cogging torque at low speeds, this can be reduced by using sinusoidal (AC) commutated drives, but these tend to be more expensive.

[runinbymdnt]

Thanks for the replies
The next question is on the drives. The drives I have with these are new, state of the art, current limited (at 50 amps), reversable, small Industrial vehicle speed controlers. They require 0-5v input for speed control.

From what I have told you here, does it sound like I could use them as servo drives?

Is there a way to test or identify their usefulness?

I have been hanging around this forum for a while now. I have learned so much I cant believe it. With resources like this forum, ignorance is difficult to maintain.

Thanks again JK

[ger21]

If they are 0 to 5V, how would you reverse them? Most servo drives would take a + and - voltage to have forward and reverse. If I'm wrong, someone please correct me.

[NC Cams]

In addition to the 0-5v speed input, you'd better have a separate direction bit or else things could get real interesting.

That or else it is purely a unidirectional speed controller which would make it a challenge to use in CNC where you typically do need bidirectional drive capability.

[Al_The_Man]

I suspect the input could be ±5v, otherwise as the others say, you will need reversing method.
As to Brushless, there are two basic types DC brushless and Sinusoidal. I have found the DC brushless noisier than DC brushed because of the large pulses when commutated, they also do exihibit some cogging if used as direct drive at low speeds, as has been said.
AC sinusoidal are extremelly quiet, smooth and excellent at low speed.
If you show a link or post info on the drives, more can be said as to how usefull for servo use etc.
Al.

[runinbymdnt]

We currently use a seperate imput for reverse but I think they are configurable to except -5 to +5v . That would be called a wig wag throttle and would be used on say a pallet jack. I will check that out.

Is the imput voltage of -5 to +5v exceptable? What do other drivers use?

I would gear them down as the rpms are too high to direct drive, that should help with any cogging issue, however these motors are very smooth and quiet.
I have used and disgarded some very noisey brushless motors. I looked long and hard to find these for my vehicle aplication and buy them and thier controlers in large quantities so the price is good.

Great info. The magic of the "black box" in a cnc machine is starting to make sense. Bye bye to a little more ignorance.

Thanks again JK

[Al_The_Man]

Most analogue controllers use ±10vdc but can be scaled. Check to see if there are other options of control, It depends on what you intend using as control, for example, most Software/Parallel port systems use step & direction in place of analogue.
It depends if you are using them in a CNC application or a stand-alone system.
For precision positioning etc, you will also need encoder feedback.
Al.

[ger21]

You can convert the step and dirction to analog with these.
http://www.skyko.com/products/

[runinbymdnt]

Thanks Al
I new I would have to add encoders, that should be no problem.
I dont understand the stand alone system??? I am building a large steel and aluminum cnc router to start, then I think I will cnc my mill, why not. I always thought cnc was black magic or rocket science, something I would never have. I now know I was mistaken. It's realy quite straight forward as I have spent a couple dozen hours reading on this site and others.

Is there a simple explaination of step and direction as opposed to analog?

If using what I have gets too crazy, I will buy what is needed to simplify things. I want a good system when I am done.

I have been fabricating a wide range of things for most of my life. Everything changed for me 2 years ago when I took 6 months off and taught myself to solid model using solid edge software. Wow. That has me off in a new direction.....digital. I still have alot to learn and am loving it.

Thanks for the help JK

[runinbymdnt]

you guys are fast.
You are answering my questions before I can ask them!!!!!!

Thanks Gerry

JK

[Al_The_Man]

Is there a simple explaination of step and direction as opposed to analog?

Sometimes we answer before you ask-em

This will depend on the system of control you decide on, for example if you go the route of most here, the likes of Mach2,3 etc, then you will need step and direction drives or converter as Gerry pointed out.
Your drives are analogue so you can only use them without convertor on a compatible Analogue control system like A motion control card such as Galil/Camsoft et. al.
The motion control card system closes the loop in the controller, the software solution does not, you pay for the difference.
Al.

[runinbymdnt]

I looked at the boards Gerry pointed out and they are $ 69-79, no big deal.
Is this the way you would go?
I dont understand it all yet (it is slowly getting clearer)
or would you scrap my analog controler and just buy the appropriate driver?

My controlers are rock solid and 50 amps. Thats lots of power. Is all that power needed or desirable?

You have most likely allready advised me while I was typing this..... I'll hit the post button and find out

Thanks JK

[Al_The_Man]

At this point you are asking the wrong guy, I have not used parallel ports sytems, but I would say if you have nice (expensive) drives already, it would not hurt to investigate the Skyko board conversion alternative.
Al.

[runinbymdnt]

Well, I called the co. motor controler guru and caught him before his coffee on a sunday morning and asked some questions about our motor/controlers and the possibility of configuring them to work for my cnc aplication.

No can do. The flexibility was cut out of the controler design several months ago to save cost.

Like a dog eating a steak....... NEXT.

I still have some very good brushed motors that I used for prototyping. So it looks like. add encoders, buy drivers and I'm good!!

Any problems with that?

The only other option is steppers. from what I have read I am ok with servos.

Any problem with my thinking here?

I love it when the answer is No sometimes, it makes things simpler. I have a way of making things more difficult than they need to be. Can any of you guys relate to that?

Thanks for the education Al, Gerry and others, it wasnt in vain.

JK

[runinbymdnt]

sorry for the double post, I still have computer issues.
JK

[Al_The_Man]

Do you know if they are DC Brushless motors? if so they should have some kind of Hall effect commutation or equivalent, these motors are generally easier to match up to different drives than sinusoidal.
Don't even the DC brushed motors have encoders? Are they servo grade?
You can usually get Brushed drives from A-M-C or Copley Controls.
Al.

[runinbymdnt]

No the brushed motors are not servo grade. They are just run of the mill but good traction motors. Thats right. I had forgoten that the brushed motors have to be (dont know what you call it) ballenced to run the same in both directions. Correct? No they do not have encoders, I was planning on adding them.
What is sinusoidal?

Is it possible that I can still use the brushless with new properly matched drivers?
What will I have to find out about these motors to determain if I can use them (the brushless) ?

Sorry for so many questions but I guess this is what this forum is all about, I hope.

Thanks JK

[Al_The_Man]

You need information details as to the type of commutation device fitted, preferably with pin out.
Are the brushed dc wound-field or perm. magnet?
Usually traction motors are series connected, which makes them usless for servo app.
Al.