Dear all,
after doing some survey in the market, I've finally come out with 2 choices of stepper motor that i'll be using for my 1st CNC project:
1) Vexta PK268-E2.0B (4.5V, 2.0A, 187oz.in, 0.000048kgm2 rotor inertia)
2) PowerMaxII P22NXXE (4.4V, 1.64A, 195oz.in, 0.000025kgm2 rotor inertia)

They're both brand NEW and Vexta is slight MORE EXPENSIVE (about 6 dollars more only) than PowerMaxII....

Since they're both very well-known and specs are almost similar, would anyone here suggest which one should I go for??? Or, have i missed out other consideration/parameter?

Correct me if wrong.... Thanks alot guys!
Andy

What drivers are you going to use? Can you get the Powermax with different windings (P22NXXD, P22NXXC)?

Gerry, I'm planning to use 8051 uController + L298 (+L6506 for current limiting) as my driver. That means 2A (RMS) for each phase and microstepping with chopper as current limiting. Nothing is bought yet, still in decision making though!

I think it shouldnt b a problem to get D or C winding, but the current is apparently higher for Parallel Bipolar (2.5 for D and 3.1 for C if not wrong...)!

Thanks for you info!
Andy

Then it really shouldn't be that much difference between the original 2 motors. If the driver had a higher current rating, I would suggest one of the other motors. That's why I asked.

ok... i got u! thanks again....

But i have a feeling that Vexta has better power output, judged by its Voltage x Current is HIGHER than PowerMax... anyway, i'd like to hear more inputs since i still have a few days before deciding on which i should buy.

Cheers,
Andy
ps: Do u think D or C connection has much better HIGH RPM torque versus E type connection?? i cant find any speed-torque chart for both Vexta and PowermaxII, even Vexta has a graph, it doesnt state if it's a bipolar series or parallel.... kinda hiding it to prevent u from comparing with other competitors.... :P

The rating you gave for the Vexta is unipolar. Look here: http://www.orientalmotor.co.jp/cgi-bin/WebObjects/UPOMStep.woa/wa/F3?typeNameId=1&modelName=PK268%2DE2.0B&seriesId=2PK&frameSize=56.4

The Vexta is rated 260 oz-in bipolar. But it is 2.8a, 3.2V bipolar parallel. I'd think about using a Xylotex to run it at 2.5a bipolar parallel @ 24V.

Or better yet, if you want to build your own driver anyway, look at the drivers at http://www.embeddedtronics.com

These can be run at a higher voltage. High speed needs higher voltages. So, at a given voltage, the C or D windings should have a higher top speed because they have lower voltage ratings.

Thanks alot Gerry, for the link to the Bipolar Series/Parallel Torque-Speed chart of Vexta Stepper!!

Wish i could run these Vextas using what Embeddedtronics is using, the LMD18245 driver chips. Each motor needs 2 LMD18245, added up to the total cost of <<<8>>> times more than if i were using L298!!! a 1.0A increment over L298 really costs alot yo!

So, i m thinking if it's possible to PARALLEL 2 units of L298 to get a current rating of 4A??? If that's feasible, my cost will be REALLY cut down to double instead of 8-times more! Has any1 tried out this method? Gerry?

BTW, that Bipolar Parallel connection of Vexta PK268 has 2 very steep resonance points as compared to only 1 mild resonance point with Bipolar Series.... Is there anyway to "compensate" this disease using software??

Thanks man!
Andy

and... embeddedeletronics microstep circuit looks very ROBUST and clean design with PIC and 2 x LMD18245!

I'd really like to make a 8051uController and some driver chips to control all the 3-axis and it's NOT 1 8051 per axis... still finding for any materials about how to do it since i'm not a strong programmer.... only used it a few times before, i mean 8051 uC.

BTW, that Bipolar Parallel connection of Vexta PK268 has 2 very steep resonance points as compared to only 1 mild resonance point with Bipolar Series.... Is there anyway to "compensate" this disease using software??

Thanks man!
Andy

Microstepping should smooth this out quite a bit, I believe.

Hello thete:
I´m trying to make a generic current limiter to use on phase-drivers. Anyone can help me ti figure how the L6506 works? like a minimal schematics and how to put some potenciometers to make a generic " CHOPPER " ?
Thanks!

So, i m thinking if it's possible to PARALLEL 2 units of L298 to get a current rating of 4A??? If that's feasible, my cost will be REALLY cut down to double instead of 8-times more! Has any1 tried out this method? Gerry?

BTW, that Bipolar Parallel connection of Vexta PK268 has 2 very steep resonance points as compared to only 1 mild resonance point with Bipolar Series.... Is there anyway to "compensate" this disease using software??

Thanks man!
Andy

See figure 7 of the L298 datasheet. The chip outputs can be paralleled to get more current. I haven't tried this since I gave up using l298 for driving stepper motors and designed a driver using the LMD18245 about 2 years ago. I could not completely solve stepper motor resonance issues using the L298 driver. To many wasted parts on my mill due to resonance miss steps. Switching over to a microstepping driver has completely solve that problem.

If you really want to design your own stepper driver, I recommend you look at the datasheet for a Allegro SLA7062 3amp microstepping driver chip. I recently received my samples and will be designing a board with them.

The LMD18245 is a expensive chip but there wasn't to many options available when I did the original design for my microstepping driver.

Jim
www.embeddedtronics.com