Mini CNC router, complete plans and instructions

Step 6: Electronic components - Motors

The motors chosen for this project are 3Nm 8 wire stepper motors that can be wired as unipolar or bipolar, depending on everyone’s choice or what driver you have (unipolar or bipolar).

   -  3 pieces of 3Nm stepper motors    

A unipolar stepper motor has two windings per phase, one for each direction of magnetic field. The motor has only five leads.
Bipolar motors have a single winding per phase. The current in a winding needs to be reversed in order to reverse a magnetic pole. There are two leads per phase, none are common.


The difference is: “Unipolar and Bipolar Half Coil, because we're using less turns, doesn't give us great low speed torque, but because of the low inductance, holds the torque out to high speeds.
Bipolar Series uses the full coil so it gives very good low speed torque. But because of the high inductance, the torque drops off rapidly.
Bipolar Parallel also uses the full coil so it gives good low speed performance. And its low inductance allows the torque to be held out to high speeds. But remember, we must increase current by 40% to get those advantages.”
 

Comments

[mgimbel]

did you really have to use such big steppers, I mean for a lot less you could have got weaker steppers that are better suited for this task. I dont think you'll ever use their 425 oz. capacity

[thepainkill]

http://www.youtube.com/watch?v=-5ULOYQ7CuE

[erick3525]

First of all, nicely done! As for the stepper sizing, they will only really be oversized if the power supply and driver are not capable of meeting their potential or they are capable of damaging the machine. If all of the electronics are well matched and the machine is free of binding and so forth, larger motors will allow much higher feed speeds to be attained reliably, especially while cutting. Materials that the builder is most likely to intend to mill out with this machine will be able to be be cut at high feed rates.