Unipolar or Bipolar ???

[Milton]

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

Unipolar or Bipolar

Thanks
Milton

[BobWarfield]

A detailed discussion is here:

http://www.st.com/stonline/books/pdf...sadvantages%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

[Milton]

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

Milton

[project5k]

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...

[Madclicker]

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.

[ger21]

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.

[Milton]

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

[BobWarfield]

Originally Posted by ger21 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

[Rhodan]

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.

[ger21]

Originally Posted by Rhodan 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?

[Madclicker]

Originally Posted by ger21 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

[BobWarfield]

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 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