What choice for stepper motor : unipolar or bipolar

[gaga2410]

motor unipolar

Hi,

I'm wondering what configuration to choose for my cnc machine.

I have 6 wires stepper motors wich can be use as unipolar or bipolar.
What are the differences between this 2 modes ?
What is the best choice ?

Thank you for your advice.

 

[simnav]

difference unipolar bipolar stepper motar

The main difference is the driving method: in bipolar stepper motor you have two coils so 4 wires and you need an H-bridge driver to be able to change current direction into the coils; in unipolar motors the two coils are divided in two parts each; those parts are linked in one point: in this way if you connect the common node of each coil to the supply voltage, it's sufficient to connect to ground one of the other two leads of coil: one lead will flow current in a way, the other in the opposite. An H bridge requires more control logic and four transistor per phase; for unipolar motors only two transistor per phase are necessary and a more simple logic.
There is another difference that pheraps interests you more: the preformances! Considering same size motors unipolars have in general less torque than bipolar since only an half of the coil is energized each time, anyway it is necessary to consider that for the same reason bipolar motors have a greater resistance so with a given current power dissipation will be greater than with unipolar.
What's the best solution? It depends! Do you prefer a simple driving circuit or more torque? If you need to choose a motor for your application I suggest you to check torque characteristics of some motors and pick the better for you.
I hope this help you.

Regards,
Simone Navari.

 

[gaga2410]

Thanks for this very helpful reply.

But, can you explain to me what is torque please ?