Driving a Size 23 Stepper Motor

[Circuit]

I have just acquired a size 23 Hybrid Stepper Motor (Astrosyn MY23HS2-2) and I want to drive it using a PICAXE. I have driven smaller motors successfully, but I would be grateful for a little advice to check that I am thinking along the right lines with this one...

The motor is an eight lead type so can be driven either Unipolar or Bipolar.
The Phase Current is specified at 1.0A and the Phase Resistance is 6.2ohms.

Therefore my understanding is that to drive this without current limiting I should be looking at 6 volts for unipolar drive and 12 volts for bipolar drive to sustain one amp phase current. An L293 (not L293D) is specified to drive 1amp per channel with a 5ms peak of 2 amps. I would like to use the L293 as a bipolar drive with the necessary external protective diodes rather than upping to an L298 simply because the former is easier to work with. Before I set it up and try to discover for myself at the risk of burning out some L293s, could I ask for advice or experience, please?

A further question; I do have some 2 amp 4-phase unipolar stepper motor driver boards (RS Components, 217-3611) which operates at 12 volts but requires a current limiting resistor placed between the board and each phase winding - in this case it would be a 6 ohm resistor rated at 10 watts. With a mind to more sophisticated driver units that offer adjustable current limiting on board, I am thinking of using an LM317 wired for current limiting as a substitute for the resistor. A commentary on this approach would also be most welcome.

(edit) I have just read one of the references given by Westy in his most well-written tutorial on stepper motors which states "The performance of a motor run with a current limited power supply is noticably better than the performance of the same motor run with a resistively limited supply" therefore this reinforces my second question - is the LM317 the right way to achieve this?

 

[WHITEKNUCKLES]

Greetings Circuit,

I have successfully driven steppers directly with Picaxe from 08 up to 40 but it is easier, more effective and can be cheaper to use a ready made chopper driver.

Over specify all power components with regard to Datasheets or else.

Your 1A through 6R2 motor will step powerfully at low speed on 6V2 (IxR nominal) and cook quietly when stationary at that voltage, (fry eggs no bother).
Picaxe at 5V direct to 4 FETs through 4 wire wound re$i$tor$ or 4 LM317s plus heatsinks to PSU. Choice of Picaxe prototype board, components, multiple postage can be expensive.

Stepper motor performance is dependent on the voltage supplied to the driver.
Steppers normally take most current while near stationary, as the step time is reduced a greater portion of the step time is the rise time of the current in the coils and less at the final value. To the point where the current is still rising when the next step arrives average current drops so steps are missed and cohesion is lost.
High voltage (relative to nominal motor voltage) with chopper current limiting gives best performance due to the faster current rise time in the coils giving more time at final value.
These drivers only require a step and a direction signal allowing the Picaxe to count pulses and define direction.

I posted some test results on the forum but note that there are newer, smaller, cheaper boards. A good link in the last post.
The photo shows the separate battery for the Picaxe which needs no ground connection due to the opto isolators onboard.

Dave

http://www.picaxeforum.co.uk/showthread.php?25336-TB6560-Stepper-Driver-Board&highlight=stepper+driver