What is the benefit of unipolar op of a bipolar stepper?

Seems to me that the bipolar configuration gets more torque.

Is it possible to get more fractional stepping out of unipolar operation?

What is the advantage?

Thanks,

B

hmmm... let's bump this up a again.

Is this the right place to ask a question like this?

B

There's no benefit in performance. The only reason stepper motors
were ever sold as "unipolar" was when power transistors for drive
electronics were expensive. Bipolar drive takes twice as many
drive transistors. All modern step motor drives are bipolar, and can
be connected to any step motor, regardless of whether it is labeled
as "unipolar" or bipolar. Step motors come in 4-wire, 5-wire, 6-wire,
and 8-wire configurations, but they all have just two phases. A bipolar
drive treats 4, 5, and 6 wire motors alike. An 8 wire motor splits each
phase into two sets, which can be connected as series (higher speed)
or parallel (higher torque), but the bipolar drive still has only 4 connections.

-- Ralph

The following is from an old Compumotor guide:

Stepper Drive Technology Overview
Within the various drive technologies, there is a
spectrum of performance. The uni-polar resistancelimited
(R-L) drive is a relatively simple design, but it
lacks shaft power performance and is very inefficient.
A uni-polar system only uses half of the motor
winding at any instant. A bi-polar design allows
torque producing current to flow in all motor
windings, using the motor more efficiently, but
increasing the complexity of the drive. A bi-polar R-L
drive improves shaft performance, but is still very
inefficient—generating a lot of wasted heat. An
alternative to resistance-limiting is to control current
by means of chopper regulation. ÊA chopper
regulator is very efficient since it does not waste
power by dropping voltage through a resistor.
However, good current control in the motor is
essential to deliver optimum shaft power. Pulse width
modulation (PWM) and threshold modulation are two
types of chopper regulation techniques. PWM
controls the average of the motor current and is very
good for precise current control, while threshold
modulation controls current to a peak level.
Threshold modulation can be applied to a wider
range of motors, but it does suffer greater loss of
performance than PWM when the motor has a large
resistance or long motor cables :are used. Both
chopper regulation techniques can use recirculating
current control, which improves the power
dissipation in the motor and drive and overall system
efficiency. As system performance increases, the
complexity and cost of the drive increases.

Thare are many articles on internet about "What is the benefit of between unipolar stepper motor and bipolar stepper motor? You can search on google.