Stepper motor full stepping

Hey Everyone.

I'm trying to get more torque from my unipolar stepper motor.
I'm using a circuit similar to this
[www.elecfree.com]

Except I'm just using the 74LS194, 555 timer (not the same resistances for the frequency), and a ULN2003 transistor array.

What I want to do is change it from single stepping to power stepping ( 2 coils charged up per time )
Its a 6 wire motor, black and brown pair 1; orange yellow pair 2.
I tried putting pin 3 and pin 5 high and 4 and 6 as low.
But the motor goes back and forth.
I tried pin 3 and 4 high, 5 and 6 low; but no movement at all.

How would I make this do power stepping with this shift register.

If I cant do this, if I turn this into a bipolar motor ( ignoring the centre taps) and step it in full mode; roughly how much torque would I get versus single stepping a unipolar?

Thanks in Advance!

Sorry, the image didnt work.


[www.elecfree.com]

Hm, it seems images dont show here.

Basically It was a shfit register 74LS194 to a ULN2003 transistor array
pins 3-6 on the shift register are the inputs

You need to have two 1's circulating in your shift register instead of 1. I.e. pin 3 and 4 high.

The motor pairs need to go to every second output. E.g.

black Q1
orange Q2
brown Q3
yellow Q4

I think full stepping multiples the torque by sin(45) + cos(45), which is again sqrt(2), so if you also switch to bi-polar you could get twice the torque compared to single coil (AKA wave mode) unipolar.

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[www.hydraraptor.blogspot.com]

Thats exactly what I did though
black Q1
orange Q2
brown Q3
yellow Q4

and pins 3 and 4 high.
Thers no motion at all

Well that should be correct if the motor coils are as you stated. I.e. black and brown are two ends of a centre tapped coil.

You mention you are not using the 7474. That is there to ensure the shift register is loaded at power on by making S0, S1 both ones. If you have removed that how are you loading the shift register?

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[www.hydraraptor.blogspot.com]

I'm using just a switch and initializing it myself for now.
it works fine when its single stepping,
but I was hopign to get more torque by power stepping it

Well you will, there must be something wrong with your circuit or the wiring or the power supply. Does it give enough current for both coils to be on?

If you meter each coil, one or the other half should be on, never both off or both on.

The shift register pattern should be: -

0011
0110
1100
1001
0011, etc

Notice how columns two apart are the complement of each other. They are wired to opposite ends of the same coil so it is always energised one way or the other.

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[www.hydraraptor.blogspot.com]

Nop: You really do need to write a primer on stepper motors.

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Hell, there are no rules here - we're trying to accomplish something.

Opportunity is missed by most people because it is dressed in overalls and looks like work.

Thomas A. Edison

The 7474 was changing the S0,S1 inputs synchronously with the clock to avoid violating the setup and hold times. You may find the shift register does not load reliably without it.

Of course this is very old fashioned way of doing it. The two TTL chips are obsolete. The modern way would be to replace all the logic with a small microcontroller giving a two chip solution.

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[www.hydraraptor.blogspot.com]