RE: [CAD_CAM_EDM_DRO] Re: COMPLETE 3 axis CNC electronics package (plug-n-cut, ready to go)

HI John,

> Hi Alan,
>
> If you have a six wire stepper then it can be configured as LR with power
> going into the centre tap and one phase being one side of the winding and
> the other phase being the opposite side. This allows the stepping without
> the use of an H-Bridge to reverse the current flow in the winding; just
> single NPN transistors. Cheap!

Yup! That's where I started with stepper motors in the 70's. Darlington
transistors and even some FET designs. Unipolar drivers are simple to get
working, they don't self-destruct like an H-bridge when the bridge's drive
signals aren't correct! The SS50 and SS300 Slo-Syn steppers that I had
available are now slow compared to today's modern steppers.

>
> When such a stepper is used with an H-Bridge you get the same torque when
> you use only one half of the winding. Centre tap to one end. You get
> more torque if you ignore the centre tap and use the outer two connections
> because now your AMP * TURNS is doubled but your inductance also goes up
> so your maximum step rate is decreased -- all other things being equal.

Yes, true, but they normally tell you to use 1/2 the current when using the
full winding (bipolar), so it comes out the same!

>
> An 8 wire motor has all the advantages. Putting the windings in series or
> putting the windings in parallel or using them in six wire mode or using
> just two windings total. In parallel, inductance is halved but AMP TURNS
> is not doubled.
>
> John Dammeyer
>

8 wire would seem to be the best! However it can be a CHORE if you don't
have the color code of the windings and must work them out yourself (surplus
steppers)!

Windings in parallel are said to have the best speed. But only slightly
better then just using 1/2 the winding. It seems to me that it would be
good to use the entire winding (other considerations aside), because the
heat dissipated would be better distributed. But not at the cost of slower
speed!

I have seen a better fit for a stepper (current wise) by using the full
winding, sometimes 1/2 the current can allow you to use a smaller driver if
ultimate speed is not needed. It's good to have choices!

Alan KM6VV