Stepper Motor Control Basics

[Halfnutz]

Being new to this world of CNC and motion control in general, I have a foggy idea of how stepper motors operate but would like to understand the differences between full, half and micro stepping, chopper drives, over sourcing and all of the variations. I remember seeing some info on the web before but it wasn't focused on CNC and what we do here. I would like to ask the technically inclined around here to try and sort this out for me as well as others. Basically what are the things we need to be looking for when choosing a stepper motor and its controller. There are tons of options but very few seem to be right for a CNC application.

Thanks.

[mark c]

Good question Halfnutz!
I too would like to know this, as well as many others here. I'm going to convert my Rong Fu to cnc pretty soon and will find this info invaluable as I determine what I need, ie servos vs. steppers etc

Looking forward to it

[Halfnutz]

Ok, just to get things started,what's the difference between a DC and a AC step motor? Both require a TTL pulse signal right? You cant run a DC stepper off of straight DC can you? Whats the simplest way to get a stepper to turn? Can I hook it up to a 12 volt power supply to see if it works?

Another simple question. What is a chopper amp? Why are they desireable?

How about microstepping. Is this just increasing the frequency of the pulse stream? What is the frequency that steppers run at?

Come on guys, help us morons out a little.

[ger21]

AC motors would run off AC current, DC from DC current I haven't seen any hobbiests using AC steppers, but Oriental Motor does make them. Very expensive.

You can turn a stepper with a battery, but don't use a higher voltage than the motor is rated at.

You might want to read this about microstepping. http://www.machinedesign.com/ASP/vie...strSite=MDSite

[ESjaavik]

Read this: http://www.cs.uiowa.edu/~jones/step/ first.

[Halfnutz]

Wow, the last month has been a learning experience. I finally have an idea of what is going on between the keyboard and the leadscrew now. I finally settled on Centent controllers. They are the most expensive boards I have been able to find, and they go for dirt on ebay occasionally. I put together a set of 2 Centent 0162's and 1 0142 for less than 200.00. The retail for these would be 1350.00. I have no idea why they are so much, but they better be good, for that kind of money. The specs and packaging are pin compatable with gecko's. Theyre made in the same town as Gecko's are, but they cost 3-4 times more. Thanks for both of those websites, they helped a lot.

[mannster]

So, under "real world" conditions, has anyone experienced anything that may reduce the importance of microstepping ?

I know that motors do resonate easily when they are not hooked up to anything.
But, I think that when you are pushing a mill table, that probably dampens the resonance.
Torch gantries probably have a resonance problem due to the fact that they are basically rolling frames (ie: lighter, less weight to dampen vibration).

I read somewhere (forgot where ) that more than 8 microsteps per step is overkill.

Who wants to comment for or against microstepping ? Some folks may think that they need to spend more for something they don't need. (*Is chopping enough for them ?)

I think either way is fine, but I would like some input so I can learn more about driver technology.

[ger21]

Halfnutz, I'm pretty sure that Mariss from Gecko was the designer of the Centent drives, before he started Gecko. They cost more because they can sell them for that price.

Mannster, all the chopper drives I'm aware of do have microstepping. The only ones that don't are the unipolar drives like the Stepperworld drives.

[Halfnutz]

Yeah I figured something like that was up, they are so similar. So basically I got Gecko drives, as far as function goes. Well thats sweet, with the eaton leonard PS I got for 20.00 ( +48V @ 6A, +24V@15A,+5V@5A) and the 2 900 oz/in steppers for 50.00 I should be able to open garage doors. The "little" gantry router I started planning keeps getting bigger and bigger. I may save this setup for a mill though. I think its probably overkill for a router.

[mannster]

Yes Ger21, most of the drives known here probably do include microstepping, but chopping refers to keeping the same Current level as speed increases, while microstepping breaks each step into small segments that create a sine wave, which leads to a smoother movement.

I am starting to think that drivers either chop or microstep, but I am not sure, and that is exactly why I brought it up here.

[ger21]

Originally Posted by mannster I am starting to think that drivers either chop or microstep

Most good ones do both. And just about all commercial choppers microstep, but I believe you can get schematics for ones that don't. (297/298 I think).
You might want to read this.

[ger21]

Originally Posted by Halfnutz So basically I got Gecko drives, as far as function goes.

Geckos are probably a bit more refined, and may have more features, but I'm not sure. I've seen people here use Centent drivers with good results.