stepper motor question???
 

I purchased some stepper motors quite some time ago. Thay are Vexta oreintal motors and they say .72 step and 5 phase.. They are Nema 34 motors..I also have the Vexta drivers that supposedly goes with them.. I know more info may be needed but for my question, do these appear to be useable for a MMate cnc machine...Thanks

The Version of the motor should be needed to find out if they are adaptable. But Nema34 is the desired size for the MM. 3-4Nm without gearing is definetly needed. If with gearing then you can go to 2Nm. As far as I know.

5 phase motors are a rarity for us - I'm not aware of anyone using them on a MechMate. If they fit physically, have sufficient torque, and you have drivers for them, they should work. But I don't know that we'll be able to help you much.

Tom,
I am very familiar with the 5 phase units. As long as you check the torque and speed specs of the motors you have, you should be fine.

Just be certain to set the input on the drivers to step and direction and not CCW/CW or Vacuum. The OM site has VERY detail specs on how to set this up.

You should watch out for that 0.72 degrees for step, steppers we all use have 1.8 degrees step angle. It means you will have 2.5 times more precise movement than others, but also that times higher pulse rate in mach for step and dir signals.

stepper motors
 

Thanks to all for response...Danilo, what does the higher pluse rate , etc you mention translate into as far as mach??? Slower travel speeds??? just more difficulty in set up??? Thanks

Generally, it means that Mach will have to stream a higher pulse rate to match the drivers. Mach default process rate is 25Khz....but can process as high as 45Khz. You may find that you need to set your configuration to this higher rate to achieve the desired results.

In testing over two years ago when I went to the OM class on 5 phase units and such, my Mach settings were on the default 25Khz and all performed well.

good luck.

Its simple calculation between steps and speed of travel. some computers don't work reliable on rates above 25 or 35 kHz in Mach3.

If you use them ungeared and with drivers that use 10 microstep then for one rotation of motor Mach must send 5000 pulses. 10 microstep * 500 steps in rotation.

so with 25 kHz pulse rate it should be able to rotate 5 rotations per second or 300 RPM and then if you use 30 tooth pinion module 1 (30 *3.14mm) it translates to 28 meter/sec . Which is enough I think. If I got wrong somewhere in calculation please correct me.

If you were to gear them then divide 28m/s with gearing factor to get maximum speed.

Looking at numbers you will be OK with these motors I think. Just find compatible drivers.

Stepper motors have a fixed number of steps per shaft revolution. A 'standard' motor has 200 steps per revolution. A half-step motor has 400 steps per revolution. A 'standard' motor used with a Gecko stepper driver has 200 X 10 steps or 2,000 steps per revolution.

The motors that you listed have 500 steps per revolution (360 / 500 = 0.72).

Usually, 500 steps per revolution will not give you the resolution needed on a CNC machine. If you use a 1.25" pitch diameter pinion gear, each revolution of the motor's shaft would move an axis 3.927". When you divide 3.927" by 500 steps, each step would move the axis 0.007854" or 1/127th of an inch.

If you build a belt-drive and gear that stepper 4:1, each step will move the axis 0.0019635" or 1/509th of an inch. That's much better and probably acceptable because machine flex will keep you from getting repeatable results better than that, even if you use a motor/driver/gearing to get 0.001" per step or less.

I have used 5-phase motors - years ago. They were smoother than the standard motors, but today's 'square' style motors and Geckodrive stepper drivers, have both better resolution (small distance per step) and greater torque.

Oriental motor now offers the AR98 series motors that are 5-phase. They cost $762 with driver and have about the same torque specs as the PK296 size motors. A PK296 size motor will cost $138 and a G203v Gecko stepper driver will cost about $155, so the Gecko/PK298 package will cost less than half as much as the AP98 motor. The Gecko/PK296 motor package will have 4X better resolution.

So, for new designs, I recommend the PK296 or PK299 series motors with Gecko G203v or G201x stepper drivers.

@ Richards, I've just started trying to figure out this CNC stuff and have a question on the motors. I looked up the PK296 series on the OM web site and they list quite a few selections. I noticed on Sean's builds he used 7.2 to 1 geared motors but those come in different sizes and different bi polar and uni polar ratings. What would be the motor of choice to go with the Gecko 203's and whats the value of geared vs straight.
@ Sean what specific motor did you use and why? Since you use your machine on a daily basis that must have been a factor in your motor selection.
TIA
Dan

Dan, the PK296A2A-SG7.2 has been one of the commonly used motor configurations for the MM; many of the early builds used these motors, and they are still the reference standard for those using geared motors. If I'm not mistaken, Gerald's initial build used them as well. The alternative is to explore the belt drive systems, which allow using much less expensive motors, but a more involved assembly process and additional components.

Dan,

I used the PK296A2A-SG7.2 and G203 drivers for my first machine. My current build is using the same PK296A2A-SG7.2 with the G540 combo drive unit. The 540 requires a very specific range of inductance coil motors for proper application, but the OM geared motor fits this requirement. The cost difference with the combined driver and breakout board offers significant savings.