Just some quick questions.

[elliottjempty]

First off, I know very little about servos, steppers, drivers etc...

But I really want to build my own cnc router, I got to use a Haal cnc lathe and mill the other day and it was awesome. I tend to work with wood more often and would like to build my own table.

I've done a lot of research and decided that even though I don't know **** I want to use AC servo motors and drivers. I started looking around on ebay and it seems that finding ac servo motors is pretty easy, and they really aren't that expensive. But what I really don't understand is the drivers.

For stepper motors the driver makes sense to me but for ac servos it's more complicated.

So what I would like to know is if Ac servo motors and drivers have to be matched, and in what way? Do AMC drivers work for an ac servo motors or just a range or just a specific motor?

I know these questions are probably kinda annoying but I couldn't find a thread that made it click for my brain.

thanks,
Elliott

[Al_The_Man]

Although virtually constructed the same there are AC and DC Brushless (BLDC) motors, however the drives are quite different for each.
Here is BLDC example.
http://users.tinyworld.co.uk/flecc/4...otor031102.swf
For the motors, the difference is in the commutation.
Al.

[elliottjempty]

That makes sense, really nice graphic. So what should i be looking for in purchasing. On ebay there is a ton of ****. Can i just get ac motors and drivers separately or do I need to buy matched parts? How do I know if it bldc?

[Al_The_Man]

In many cases you have to track down the Manufacturers literature, as some ebay sellers list BLDC as AC servo's.
It is my experience that the ease of mixing and matching servo motors to drives in the following order starting with DC Brushed easiest, next DCBL and AC third.
With AC sinusoidal the commutation is often done with Resolver etc, and these often have to be matched to the corresponding manufactures drive.
Keep in mind that if you intend to use Mach or Parallel port type control, you should look for Pulse and Direction command capability in a drive.
Al.

[Altra]

Hi Elliot,

Servos may not be the best way to go in the beginning. Like Al said, Most of the software to run cnc machines are geared towards stepper motors. Servo controllers you find on Ebay such as the AMCs are controlled using "CAN" which is a serial network protocol or are analog voltage to change speed and direction. Then you need to match the motors to the controller. Brushed DC, brushless AC/DC does the motor have an encoder, tachometer or hall effect? You can see there are a lot of variables!

Thousands of people on these forums are using stepper motors! The things they are making are fantastic. If you use microstepping they run smooth.

I have used servo motors with encoders and the Gecko 320 drive which is one of the few servo drives which accept step and direction commands. This might be a good way to go if you really want servos instead of steppers.

Regards
Mark

[Torchhead]

I would not recommend trying to build a CNC project from unmatched drives and motors. It's dicey with Brushed DC; worse with BLDC and AC Servo. One of the reasons there are so many AC servo's on EBAY cheap is that the drives you can get that will interface to affordable control software are typically not available, or lots of $$$$. There are a myriad amount of land mines and if electronics and power systems are not your area of expertise, doing it with components where even the guys here can't help will be a frustrating experience.

I'm not sure how you ended up at the AC servo solution but thousands of tables have been built using the easier to integrate stepper and DC brushed servo drives. There are pros and cons for EVERY type of system. Unless you don't mind wasting money on a learning experience the approach of doing things understood and supported by the majority of DIY builders is the more prudent approach.

Even the choice of stepper VS servo is surrounded by lots of misinformation or emotional reactions rather than engineering facts.

Concentrate on what you want your machine to be able to do. Look at the available options for controlling that machine and the software to create the drawings, the software to define the toolpaths [CAM] and the software to control the motors. That is as important a part of the machine as the hardware and if you don't select a solution that will "meet up" it will end up a dead project.

I have 2 AC servo drives and motors that were given to me a couple of years ago. They are older technology and need that vendors proprietary software and interface to run. About the only thing that makes me not put them on ebay and find a pigeon is I could possibly use one as a spindle control for a lathe.....but that will probably never happen. At some point they will become like the stack of 5 phase Berger steppers I have....not worth the storage space.

TOM Caudle
www.CandCNC.com