Like to get some feed back on which is the best system to use and why

Unipolar or Bipolar

Thanks
Milton

A detailed discussion is here:

http://www.st.com/stonline/books/pdf/docs/1679.pdf#search=%22unipolar%20bipolar%20stepper%20advantages%20disadvantages%22

Bipolar is better. See the paper for discussion details, but the bipolar will produce more torque. The controller required for a bipolar may be slightly more complex, but it's worth it.

Best,

BW

Can use 6 and 8 wire unipolar in a bipolar set up and be as good as a 4 wire bipolar stepper.

Milton

good write up...
now im fairly new at this but let me take a stab from what i understand..
you can use a 6 wire motor, but you need to know which are the 2 centertap wires, and just dont use them.. this will work.. also with an 8 wire motor, you can do 1 of 2 things, figure out the order of the windings, (a dat sheet would be very usefull here) and then you can series each pair of windings, or you can parallel them.. some pros and cons to each.. series, increases the V rating, and thus requires a higher V supply, but this will also increase the inductance, and thus will require bigger shunting diodes to take care of the magnetic decay pulse or reverse EMF... parallel can use the rated voltage, but will require an increase in current supply ie larger drivers... as to which is better, i think it kinda depends on your particular application, torque requirements, power supply, and the drivers that you are going to use...

I'm building my own drivers, so i can adjust them as i need to.. but i am definately using a bipolar system due to the larger torque that can be produced... I'm planning to use a L297-L298 pair for each axis... i can post a schematic of this if you like, or there are lots of them on the net for free... i just received my parts from digikey, so im going to start breadboarding it up, and try some modifications for a siginificant current increase...

The L298 will handle 2A. Not gonna power a big motor. There is a way to parallel the drivers on the chip to get 4A. It's in the data sheet. Then you can use 2 to drive a motor.

Bipolar does not produce more torque than unipolar, unless your using 8 wire motors.

A 200oz in 6 wire motor will have 200oz in of torque with a unipolar drive. A 200 oz in 4 wire motor will have 200 oz in with a bipolar drive. You don't get more torque just because it's bipolar. You have to consider the whole package. Motor, drive, power supply.

If both unipolar and bipolar are 200 oz holding torque and are moving at 360 rpm with a 6 turn drive screw for 60" per min both will have same torque at that speed ?

Milton

Bipolar does not produce more torque than unipolar, unless your using 8 wire motors.

A 200oz in 6 wire motor will have 200oz in of torque with a unipolar drive. A 200 oz in 4 wire motor will have 200 oz in with a bipolar drive. You don't get more torque just because it's bipolar. You have to consider the whole package. Motor, drive, power supply.

But Jerry, you can't take a motor rated at 200 oz in and run it either bipolar or unipolar and have it produce the same torque. The 8-wire example produces more torque precisely because you are able to run it in both configurations with the same power supply. The Thomson article I linked to says the same motor on the same frame will produce 40% more torque when wired bipolar than unipolar. Hence my statement that bipolar produces more torque stands. To argue that a bipolar system designed to produce 200 oz in has the same torque as a unipolar system designed to produce 200 oz in just doesn't seem to answer Milton's original question or shed much new light on the subject.

Best,

BW

The important point here is the motor rating. If its rated at 200oz/in then it doesn't matter what type it is, its 200oz/in.

However, if you take a 200oz/in unipolar and wire it for bipolar then you get more torque out of the same motor and its no longer 200oz/in. To get that extra torque you sacrifice some micro-stepping ability - where you had four windings you now have two - not as many combinations to position the rotor.

The important point here is the motor rating. If its rated at 200oz/in then it doesn't matter what type it is, its 200oz/in.

However, if you take a 200oz/in unipolar and wire it for bipolar then you get more torque out of the same motor and its no longer 200oz/in.


Correct me if I'm wrong, but if it's a 6 wire motor, you won't get more torque running it bipolar, will you?

Correct me if I'm wrong, but if it's a 6 wire motor, you won't get more torque running it bipolar, will you?

You get something like 25% more torque bipolar. I have 3 of these m112 motors:

Stepper Data Sheet (http://mcsupplyco.com/uploads/productlayouts/ProductDetailDisplay.asp?DirectLink=true&ProductID=1212)

Crazy confusing stuff, isn't it? Stepping aside (badum bum!) from bipolar vs unipolar, there's all the other good stuff needed to optimize stepper performance. Microstepping was mentioned (but can I rely on it for more accuracy--no probably not), power supply (you mean I want 20x the rated voltage, come again, that can't be right?), parallel vs serial windings on an 8 wire motor, yada yada yada.

Now add to that the other crazy confusing discussions we have over and over again:

- Should I use steppers or servos? Whoa, all that stepper stuff seems simple compared to servos, but the real pros use servos, but can I afford them????

- What kind of leadscrews? ( aka Why can't my acme screws be made to perform as well as expensive ground ballscrews? )

- What kind of angular contact bearings should I use and how do I mount them? ( aka, I just want to use $7 skate bearings but NC Cams will kill me if I do )

And that all time favorite, "I just bought a drill press at Harbor Freight and wanted to share my plans to make it perform as well as a Haas vertical mill."

Simpler questions include, "I just bought this really cool <substitute any linear motion part here> on freeBay for a song. I want to base my entire machine around this one piece. How do I get all the other pieces to make it work just as cheaply?"

But you know, that's what makes it fun. There is so much to learn, and something new pops up every single day.

Best,

BW

A six wire motor can be run unipolar, bipolar series and bipolar half coil. See my writeup: http://pminmo.com/6wire/6wire.htm

About the micro stepping, not true. You can still do micro stepping on motor with two coils, microsteping works by applying diffent current to two coils at the same time. A simple example would be to turn one coil on at 75% and the other on at 25% to get a 1/4 step position between the coils. What you may be reffering to is you can not do a half stepping that uses both on, one on stepping.


The important point here is the motor rating. If its rated at 200oz/in then it doesn't matter what type it is, its 200oz/in.

However, if you take a 200oz/in unipolar and wire it for bipolar then you get more torque out of the same motor and its no longer 200oz/in. To get that extra torque you sacrifice some micro-stepping ability - where you had four windings you now have two - not as many combinations to position the rotor.

when you micro step, dont you loose some torque? i know that from what i read half stepping dosent produce the same running torque (at a given speed) as full stepping would... its a trade off from what i understand.. 1/2 step or ustep = more positions but less torque, and full step = less positions but more running torque.. or am i completly off base.. seems to me that the bipolar is the way to go just cause then you have one coil pulling and another pushing, where in unipolar its a pull only motion... if your going to buy your drives then unipolar might be cheaper.. but if your going to build them, like i am, the bipolar is easy.. 2 chips, well 3 for my design cause i included a seperate 5v regulator.. and a few little parts, resistors and a pot... to build a 2A biplolar 2 phase drive i figure the cost like this... parts from digikey.. $9.89 for L297, $5.75 for L298, and then maby $2 for the 5v reg.. and then maby 10 for the board, resistors, pots, and other little parts.. thats not even $30 bucks.. sure theres a time investment, but it took me like 10 min to breadboard up one driver and get it working...

You can get better prices on the L297 and L298 at www.futurlec.com. But be prepared to wait a couple of weeks for the parts to arrive.

Microstepping is a dual edged sword. Less resonance, more speed and smoothness. At the majority of points in the microstep sequence there is less torque in most designs. It really depends on application as to which is the best solution.

Though I would pass on some comments from one of my users on my L297-8 pcb:

"I rec'd the boards today and they are NICE!!! Very good quality and looks like it will be easy to solder. I may use regular caps instead of the surface mount, though, as I forgot to order them. My conclusions? The board is fairly easy to build even with my ham fingers, and works as described. A good deal at 8 bucks, and good soldering practice for those of us who make our milled pads HUGE so we can hit them with the broad side of a barn."

"I even jury rigged a 5 pin Din jack and plugged it into my Nichols horizontal mill. Was able to get 10" per minute usable feed. (I squared up the ends of some 3/4" x 4" aluminum bars for a job, .100" cut at 5" per minute, 10" rapid traverse return."

"Managed to get 6" per minute rapid traverse on my Moog Hydrapoint with your board today with a 3.1 Volt 2.9 amp size 34, but had to back it off a bit on the pulse width (widen the pulse.) as I was losing a tenth or two each test cycle. Lengthened the step width 200 microseconds, stopped losing steps."

"At 3.5" per minute I was able to take cuts of 5/8" wide, .300 deep in aluminum, 1/2" wide .100 deep in alloy steel. (possibly 8620, left over from a paper mill job.) This is with an Acme 3/4-5 leadscrew, and a preloaded leadnut, as I did not want to go the expense of a ballscrew just now. My timing pulleys on the axis give me a 5-1 ratio, so I am actually cooking right along at the motor shaft. Considering that I am powering everything with a 24 volt 1.2 amp wall wart, that's not too bad. I have an older Superior Electric 24 volt 6 amp linear power supply that will run all three boards well, I think, once I get everything cabineted. Or I may build something simple into the cabinet itself......I will cross that bridge when I come to it. "

"Sorry if it seems I test everything to death; it's just a habit of mine acquired from years of R&D at various companies. It's all very empirical testing, anyway, I just know what I am looking for: consistency, reliability, and ease of use. Your board seems to fit the bill on all these points. I have developed several L297/298 boards over the years but they all fall down on noise issues. Your filtering schemes are just what the doctor ordered."

"I have been limping along on various drivers over the years; since most of my stuff is fairly low mass iron,( for example my Hardinge lathe compound slide) it does not take much power to turn the handles. My Rockwell mill, the Nichols horizontal, the cutter grinder, all these can benefit from reliability, noise immunity, and the ability to halfstep."

I have done it both way, with microstepping and without. Too me the increased smoothness is well worth the trade off for a little lost toque. It is all in what is important to you. The mill I did, I went all out and bought Gecko 201's and 640 oz nema 34 motors. I also have a 60 volt 20 amp supply and the sytem is super fast and smooth. I also have a router that has the Hobby cnc unipolar chopper board with there 200 oz motors. It works very well. On the same router had a FET 3 unipolar full step board and it worked ok, I got 60 IPM out of but it was not as smooth. I switched to the Hobby CNC set up and could get over 200 IPM and much smoother. But when all I had was the FET3 I was happy to have a working machine.

hey pminmo.. thats a right spiffy lookn board design you got there... if i didnt already have pretty much everything that i need for mine (all through hole) then i'l probably pick up a set... hmm i wonder if someone has an all through hole design that nice, or if i should just press on with building my own boards...

hey pminmo.. thats a right spiffy lookn board design you got there... if i didnt already have pretty much everything that i need for mine (all through hole) then i'l probably pick up a set... hmm i wonder if someone has an all through hole design that nice, or if i should just press on with building my own boards...

At the extra price to go double sided, soldering 2 jumper wires is much less expensive...........:wave:

i can only imagine the price diff... altho if you wanted to, you could use all that "wasted" surface area as heat sinking for a vreg, or something.. even the ground pin of the l298 will dissapate some heat to the second side... then with a good heatsink on the tab, you would really keep things cooler..
my double L298 design is a bit radical...but i'm gonna give it a shot, and when i get to that point i'll be sure to post plenty of pics...if nothing else it'll be spectacular when it goes POOF!