Vexta or PowerMaxII ??

[andyew]

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

[ger21]

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

[andyew]

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

[ger21]

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.

[andyew]

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

[ger21]

The rating you gave for the Vexta is unipolar. Look here: http://www.orientalmotor.co.jp/cgi-b...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.

[andyew]

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

[andyew]

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.

[ger21]

Originally Posted by andyew 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.

[Ito-Brazil]

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!

[jfong]

Originally Posted by andyew 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