Unipolar vs Bipolar

[Urgundiz]

Sixpence: You will know what wires are center taps with a ohmmeter. The coils 'end to end' will have double resistance that the coils 'end to center tap', and not same coil ends will show infinite resistance. Just make a table with the colors in each axis on your workbook and try all the combinations. The table itself will be very explanatory when finised.

Ynneb ed alters: Just remember that if you use a unipolar wired as bipolar you need to feed the coils with half the current of the faceplate. It is not obvious but true, and will help a lot in order to make a cheaper driver circuit.

/U

[jeffs555]

I may be wrong, but I believe that when you drive both outside ends of a unipolar motor with a bipolar driver, you only need to drop the current to 0.707 times the unipolar current. You want to keep the power dissipation(ie heat) the same, and power is equal to resistance times the square of the current. Therefore if you double the resistance by driving both halfs of the coil in series, you only need to drop the current by the square root of 2 to keep the power dissipation the same. That is why you can get more torque by driving a unipolar motor in bipolar mode. Someone please correct me if I am wrong, so I don't burn out my motors.

[sixpence]

yes, could somebody please help with answerin the above.
I too suffer form burnout fear

[ccm]

Ok, so now this begs to be asked .... can I effectively then drive bipolar steppers with a unipolar driver board ? I imagine yes you'd lose some of the torque that a bipolar driver would give you.... so, would it then use the current rating per phase listed on the motor, or draw more from the unipolar driver because it's not switching the poles at the same frequency .....?
Is this possible with the FET3 which is what I've got.... and I'm becoming more and more frustrated with because it doesn't seem to drive the unipolars I've got now......
Such a tease when the whole machine is done, but you can't make it work happily.......

thanks,

Art

[ger21]

You can use 6 or 8 wire motors with your FET3, but not 4 wire motors. If you decide to dump that and get say, a Xylotex, you could then use 4,6,or 8 wire motors. And you'd also probably double your speed.

[TimW]

Hello,
Chuch mentioned in a previous post "...Why would I want to do this? Finer detail on my work. My intention is to make clock parts -- certain gears in a clock need to be very precisely made, or it'll stop ticking....."

My interest in clockmaking is also the motivation behind my interest in getting a CNC machine running.

I ended up putting the CNC router on the backburner while I made the parts for a wooden clock using a scrollsaw and other manual tools. I found that sufficient precision can be achieved by manual means, it's just so much work and takes an enormous amout of time.

Good luck with your CNC machine and clocks.

Regards, Tim.