Unipolar or Bipolar ???

[pminmo]

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

[eman5oh]

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.

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. 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.

[project5k]

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...

[pminmo]

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."

[eman5oh]

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.

[project5k]

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...

[pminmo]

Originally Posted by project5k 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...........

[project5k]

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!