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Topic: VEXTA PH256M-33-C3 Step motor (Read 1 time) previous topic - next topic


I have been browsing through some of the information I find about CNC controllers using the Arduino, and I find a lot of useful information, but also some confusing information.

I have just started planning to make a CNC router, and I have got most of the parts, except the controller, which I will try to implement via Arduino Uno, if that is possible.

I have picke up some VEXTA PH265M-33-CS step motors for next to nothing in Chinatown Bangkok (I'm here for a vacation and will return home 16.th of July). This is a unipolar modell DC 24V 0,21A. I have read one place that high voltage give you a faster motor, and another place the low voltage give you a faster motor, so I don't know if I have made a bad choice (not a big problem - payed less than 30 $ for 4 motors).

Next thing I will need is schematics for a controller that can handle 24 volt, but I recon that will be on another forum.

Best regards

Ulf :)


unipolar/high voltage usually mean older motor/technology.

With steppers you can actually go faster whith lower voltage motors using current limiting drivers with higher than needed power supply voltage (for example a 12V supply with a 2V motor). Current rises faster because the motor inductance is lower. The faster you try to step, the less time there is for the current to rise. When the current is not high enough because you're stepping too fast, the torque is too low and the motor looses steps or stalls, so it's important to have the faster current rise possible.

So what you want for fast steppers is low voltage/low inductance bipolar motors.


For high speed stepping you need a bipolar motor with low resistance / low inductance windings and a high-voltage
supply powering a chopper-drive circuit.

The high voltage supply overcomes the back-EMF of a fast spinning motor, the chopper drive controls the current to the
correct value and the low inductance winding allows fast response to the steps.  High voltage also helps with fast response
since rate-of-change of current is equal to V/L.

Typical "high performance" motors would be 0.6 ohm 5A windings and 80V to 120V powered driver.  That's rather
extreme though, something like ~ 1 ohm 2.5A windings and 24 to 48V supply would be pretty standard.

The fast stepping mainly helps with the "rapids" for CNC, you've never cut at very high speeds (without an awesomely powerful
spindle motor!).
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]


The PH-Series is very old fashioned, but still of good quality. With the 24V coil you will not achieve high speeds. The M demarks the 0.9° fullstep types. This means even lower speeds but higher precision. The nominal torque of theese motors is less than 0.5Nm. Your will get more dynamic motors in Nema17 size for less than 30 € [1] ...

With kind regards,
Thorsten Ostermann

[1] E.g. http://www.mechapro.de/shop/product_info.php?language=en&products_id=46

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