Closing in on big order day

[Chunky]

The unipolar kits from HobbyCNC and Xylotex are really not more expensive, and the bipolar Xylotex is probably only a little more expensive.

Imo, the advertising for most non chopper drives is somewhat misleading, which results in a lot of new to cnc people finding out the hard way that they don't give very good performance.

So chopper it is. And I don't know that I even care to understand more about how it works. Choppers are clearly better and cost little more. So that gets me down to uni versus bi. I don't mind doing my own research but so far all the material I find leaves me confused. Most people on this forum probably have electrical/electronic backgrounds. I don't. I'll appreciate any suggestions regarding links where I can find tutorials describing the advantages of bipolar motors over unipolar and vice versa. Thanks to all.

[Chris D]

No, really, we meet every thursday, or is it Tuesday :-(

I have the Hobby CNC board with unipolar motors. The motors I have are from Stepperworld when I bought their L/R drive system (I didn't like that driver at all). The motors are the old 160 in. oz. motors that are gray in color and look like they are from the 60's or 70's. One of them was giving me troubles, so I started looking for a replacement. It seems as though there are more, low priced bi-polar motors out there than there are uni-polar. While searching I kept thinking, gee, I wish I had a bi-polar driver.

I ended up buying a 200 in. oz. motor from HobbyCNC for around $50.00 - chinese made so I didn't expect too much but hoped it worked better than the old motor. My old motor was a nema 34, the new one is nema 23. I was very surprised by the vast improvement in performance between the two motors. Nearly twice the rapid speeds and MUCH better acceleration without losing steps.

As for which to choose, I don't know. Like you, I was told bi-polar is better and more powerful etc. But to me, 200 in. oz. is 200 in. oz. regardless of whether it is uni-polar or bi-polar so I don't see how they are "More powerful" when buying based on the in. oz. rating.

They do appear to be cheaper though and perhaps more plentiful on the market. I wish I could guide you more, but I can only convey my experiences so far.

Chris

Originally Posted by Chunky The unipolar kits from HobbyCNC and Xylotex are really not more expensive, and the bipolar Xylotex is probably only a little more expensive. Imo, the advertising for most non chopper drives is somewhat misleading, which results in a lot of new to cnc people finding out the hard way that they don't give very good performance. So chopper it is. And I don't know that I even care to understand more about how it works. Choppers are clearly better and cost little more. So that gets me down to uni versus bi. I don't mind doing my own research but so far all the material I find leaves me confused. Most people on this forum probably have electrical/electronic backgrounds. I don't. I'll appreciate any suggestions regarding links where I can find tutorials describing the advantages of bipolar motors over unipolar and vice versa. Thanks to all.

[ger21]

A bit technical, but one of the best sources of info around http://www.cs.uiowa.edu/~jones/step/types.html

It probably won't help you make your decision, though. I don't think you'll find a noticeable difference between bipolar and unipolar drives that are in the same price range. The only difference you will find, is when using 8 wire motors. An 8 wire stepper will have about 30%-40% less torque when used with a unipolar drive than with a bipolar drive. But, there is a more important consideration. Stepper motor torque falls off rapidly as speed increases. The higher the voltage supplied, however, the faster you can spin the motor and maintain a given torque. A general rule of thumb, is that if you machine has a given top speed at a given supplied voltage, doubling the voltage will double the top speed. Keeping that in mind, you'll generally be better off with a drive that can handle the highest voltage. So if you're using an 8 wire motor with a bipolar drive that can handle 24V, and the same motor on a unipolar drive with 48V, it's very likely that even though the unipolar drive has 30% less torque, you'll get higher speeds from the uniplar drive because it will have more torque at higher rpm's. Am I confusing you, yet?

Bottom line, imo, is buy the drive's which can handle the highest voltage, provided it can supply enough current for the motors being used. Torque is directly proportional to current, up to the rated current of the motor. A 200oz-in motor rated at 3A, will only have 100oz-in if running at 1.5A. I'ts sometimes easier to buy a drive if you know what motors you'll be using, but if you buy the drives first, there are enough motor variations that you should be able to find motors that will work well with you're drives.

[Chunky]

Bottom line, imo, is buy the drive's which can handle the highest voltage, provided it can supply enough current for the motors being used. Torque is directly proportional to current, up to the rated current of the motor. A 200oz-in motor rated at 3A, will only have 100oz-in if running at 1.5A. I'ts sometimes easier to buy a drive if you know what motors you'll be using, but if you buy the drives first, there are enough motor variations that you should be able to find motors that will work well with you're drives.

Actually, when I said bi versus uni, I was referring to the motors, not the drive. I failed to mention that. I assumed I should select the motors first though I didn't really know why.

[H500]

The main reasons for chosing a bipolar over unipolar motor is COST and size.

[ger21]

Other than the fact that you can't use a 4 wire motor with a unipolar drive, it really shouldn't matter, as long is the motor is a good match for the drive in terms of current and voltage. If buying new motors, I don't think the prices would be much different if any at all.

[Chunky]

Other than the fact that you can't use a 4 wire motor with a unipolar drive, it really shouldn't matter, as long is the motor is a good match for the drive in terms of current and voltage. If buying new motors, I don't think the prices would be much different if any at all.

Maybe this will put it to bed so I can get on with ordering.

ABC Industrial Supply Inc. has a unipolar chopper drive and 3 appropriate motors. The price is $250.00

They also have a bipolar chopper drive and 3 appropriate motors. The price is $275.00

I intend to use these on a CNC router table 24" x 24" with a 1/4" Porter Cable trim router and I will machine 3/4" MDF and 3/4" plastic plate. I intend to use the machine three times a week, two hours per session, for five years. Both packages have identical warranties, etc. Which should I choose? (a) Bipolar package (why?) (b) Unipolar package (why?) (c) Makes absolutely no difference

[Chris D]

Not sure who ABC Supply is or what products they sell, so I can't really comment specifically,

BUT!

Have you decided on controller software yet? That is another critical element in the system as a whole. For example, MACH can output step and direction signals via a parallel port, it cannot this through a serial port. Some stepper controllers/drivers use a parallel port interface and some use a serial port interface. You will need to make the decision of the software at this time too - sorry, I know it is overwhelming.

Chris

[ger21]

D) The one with the most torque, or if similar, but one can handle a lot more voltage, then the higher voltage model. (Provided you'll use a higher voltage power supply).

All things being equal, then option C.

[Chunky]

Not sure who ABC Supply is or what products they sell, so I can't really comment specifically,

ABC used to be known as ACME. They used to supply Coyote with rocket propelled roller skates, sixty foot rubber bands, and soforth. When PITA began protesting their product line, a line of gadgets clearly designed for killing road runners, they switched over to CNC components and changed their name to ABC.

[slave1driver]

Yeah- I was bummed when they stopped selling that cool stuff. The "remote triggered easy install 10x25ft steel superfast popup roadblock" was a personal fav. Even if the trigger was a little sketchy. Now I gotta find a new supplier.