L297 for unipolar?

[Mcgyver]

Phil's site lists his L297/8 controller as being for bipolar motors. Reading up on it suggests that the 297 can controller unipolar motors but uses a darlington array instead of the 298.

Yet Gecko's white paper on connections says the 6 wire stepper is identical to the 4 except the 6 has a centre tap. Their diagram shows the 6 wire hooked exactly the same as the 4, with the centre taps un-used.

so my question is, having already bought the 297/298 chip and having a unipolar motor, will it work on Phils 297/8 board if i just ignore the 2 centre taps and pretend its bipolar??

thx

[pminmo]

Yes unipolars can be run biploar two methods, but the one that makes the most sense is ignoring the center tap. I recommend you use the latest version with the LM317HV regulator.

Phil

[Mcgyver]

thanks for the help - printed the other one today at work to toner transfer, I'll reprint it next week with the HV board . it'll be my first attemp at pcb, have the tank made and all materials assembled and have read lots so looking forward to it!

[pminmo]

If you plan on a power supply 35V or less the original is fine, but you may get the bug and want to go for max speed.

Phil

[Mcgyver]

Finally got around to making the circuit board and since I snapped some photo's, thought I’d put them up - first serious electronics project!

I had a plastic supplier cut acrylic sheets to size and then cemented them together. I added an aquarium heater and bubbler. If you are going to this, the cement is very viscous and wicks into the cracks easily. The problem is that the edge left by the table saw had lots of areas that created enough of a gap that it leaked like a sieve. I bead of thicker, gap filing cement solved the problem. The etching was done with ammonium persulphate (sp?) and went fairly well.

I found the toner system PITA frankly, granted the result is fair better than bread boarding but I spent a lot of time with a loop scraping toner off the copper and inspecting traces. Also, I'd like to get away from the etchant chemical with its disposal issues and (with lots of kids running around) dangers. I don't know if my laser printer laid the toner on too thick (it was at the highest setting) or if I ironed too long or if its a typical to have to do some doctoring. For example, a problem area was those small traces between IC pins. I've decided my first cnc machine is going to be a circuit board mill (x/y basically is done).

thanks to Phil and the people here for contributing to opens source designs!

[pminmo]

Boards look great! Yes, toner transfer is kind of a pain, not my favorite thing to do. But in the end, you can take pride in "I did that", and learning something new is half the fun. Keep us posted on your progress!

Phil

[Mcgyver]

I'm with you on that one, no purchased controllers for this guy (yet)

[Mcgyver]

After made the boards, I realize with Phil’s help that I had one of the print settings set to automatically adjust the size of page or some such thing . It caused a definite, but unnoticeable at the time change in size. That was the main culprit to the trouble I had with toner traces/pads touching in some places. Round two went flawlessly.

[pminmo]

Not sure what to do to keep that from happening. Your not the first, won't be the last. Keep us posted. THanks,

[Garfield2]

Not sure what to do to keep that from happening. Your not the first, won't be the last. Keep us posted. THanks,

Other than using a Laser printer with a postscript RIP on-board (as opposed to the cheapy "do-it-in-the-driver" printers most people sell these days for Windows) and then using EPS, PS files directly to the printer there is little you can do. PDF's are the next best if you can convert them (or the printer driver does) to EPS or PCL.

Under Linux with a Ghostscript RIP driver for my Samsung ML1740 printer I just do :-

[alan@random ~]$ lpr -P ml1740 board_to_print.ps

and I get perfect results, but under WinXP unless I tune the drivers exactly right and the stars are in alignment and the breeze is blowing to the south it might print it at the exact dimensions, otherwise it's off by a few millimeters here an there. Most annoying!

I get perfect results with my toner transfer setup now. But it took a bit of patience and trial and error. I found the most critical thing was the irons temperature and pressure. To hot the image distorts and blurs at the edges. To cold and bits don't transfer or are very thin. Also a quick touch up with a sharpy fixes many things.
Alan.

[Parameter]

What is the effect of driving unipolar motors as bipolars? Resistance get double, so voltage get double or Amps get double?

What happens to torque, will I get better performances and same torque, better torque?

As do I lose some resolution? like it becomes double size steps?

Para

[pminmo]

I assume your referring to a 6 or 8 wire motor that can be run either as unipolar or bipolar. Bottom line there isn't a clear winner. Facts:
Running bipolar is stonger, rule of thumb 25%.
No difference in step size as long as you comparing equavalent steps, full step to full step, half step to half step.
If you run the same motor as bipolar then run it as unipolar with the same power supply, the bipolar wins hands down.
Sounds like bipolar is the winner, but it isn't that simple. True performance is the total system which includes cost, speed and power. Performance with all factors make it less of a clear cut. Unipolar motors are simpler to drive and cost of drivers usually reflect that. 4 wire bipolar motors are slightly simpler to build offsetting some of that. Due to the switching arrangement implenting unipolar vs bipolar, at less expense it is easier to run higher power supply voltages. Running higher power supply voltages allow higher step rates. So you could argue, that at the cost of implementation of bipolar, you could spend more money thus getting larger unipolar motors. So it starts to even out. If you already have 6 or 8 wire steppers, run them bipolar if you need max power. I have found it hard to find larger torque motors in unipolar. (400 oz in and larger)

Here is an excellent source on steppers:
http://www.cs.uiowa.edu/~jones/step/