Need Help!- Quick driver question

[hearld]

I've been working on a DIY router for the past two weeks or so and its coming along nicely. I'm a college student and this has just been a project out of bordom not so much as for anything real precise.

I was able to track down a few six-wire unipolar motors at a local office supply store, however I'm concerned with drivers. There looks to be only one type of unipolar driver on ebay but dozens of bipolar types that seem to be alot cheaper.

I've done alot of searching but can't find anything conclusive so...
Are there any downsides to running a unipolar motor off a bipolar driver?

Thanks

[Crevice Reamer]

Hi hearld. Welcome to the Zone!

You can run a six wire motor from a bipolar driver by either connecting the motor in Bipolar Series, (Good torque but low RPMs) or connecting the motor half coil. (Less torque, but more of it at higher RPMs)

http://www.cnczone.com/forums/showthread.php?t=78713.#3

CR.

[hearld]

Thanks for the quick response!

What would be the positives of going with a unipolar driver instead?
Would the benifits outweight the savings of going with a bipolar board?

Also running more than one motor on an axis would mean just running wiring in parallel right?

What are your thoughts on this driver? Is there any concern for lack of heatsink?

http://cgi.ebay.com/CNC-3-axis-6-amp...3A1%7C294%3A50

If you look at the PDF link at the bottom of that page theres a close-up of the board.

Thanks again.

[Crevice Reamer]

In full disclosure, I don't believe in ANY of the really cheap drivers. I've seen too many people have problems with them. If all you want is to see your motors move some, they may be all right for you. But if you actually want to do WORK of any kind with them, then you will soon be buying something else.

IMO, The lowest cost CNC driver that should be used is the Gecko G540. I know that is probably a lot more than you want to spend, but it DOES work well and is much cheaper than buying several lesser options and wasting time trying to get them working.

http://cnczone.com/shop/Gecko_97625.aspx

Many of the questions you will have are answered in the Basic Primer. I will try to give an answer though.

Originally Posted by hearld Thanks for the quick response! What would be the positives of going with a unipolar driver instead? Would the benifits outweight the savings of going with a bipolar board?

The only benifit of a unipolar drive is that it is very simple to make. Unipolar motors (even run half coil from bipolar drivers) have much less torque than Bipolar motors. Here's an example comparing the two:

http://kelinginc.net/KL23H276-30-8B.pdf

Also running more than one motor on an axis would mean just running wiring in parallel right?

You have to use one driver per motor. You can't just hook up two motors to one driver. I hope you really aren't thinking of actually powering a router this cheaply.

What are your thoughts on this driver? Is there any concern for lack of heatsink? http://cgi.ebay.com/CNC-3-axis-6-amp...3A1%7C294%3A50 If you look at the PDF link at the bottom of that page theres a close-up of the board. Thanks again.

MORE a concern for full step only operation that will probably resonate and lose power.

CR.

[hearld]

I am actually trying to do this as cheaply as possible seeing how I'm building this out of bordom and not planning for heavy use. Not concerned about speed either so power isn't a big deal.

If you were to guess, how much power is lost using a bipolar driver vs that unipolar. How big of a problem does resonance really pose?

I've never worked with stepper motors before, so thanks, it's helpful.

[ger21]

Get a HobbyCNC board. Tons of people haveused them, and you won't find anything better for the price. Downside, is that you need to solder it yourself.

www.hobbycnc.com

[Crevice Reamer]

Originally Posted by hearld If you were to guess, how much power is lost using a bipolar driver vs that unipolar.

Bipolar keeps most torque. With Unipolar, about 30% of the Bipolar torque is lost.

How big of a problem does resonance really pose? I've never worked with stepper motors before, so thanks, it's helpful.

Stepper Motor Basics:

http://geckodrive.com/upload/Step_motor_basics.pdf

If you MUST go super-cheap, the hobbyCNC is better than most.

CR.