Need Help!- Would this work?

[rich200313]

I was wondering if i could use a uln2804a to controll a bipolar motor, as so far i have only seen it used as a unipolar controller(i'm looking into a 3 axis machine but only have 2 unipolars and 5 bipolars, might as well use some eh?). I have attached a schematic of my idea, should this work, as long as the pins 1,2,3,4 are pulled high in the right order? I would try it myself but i have no diodes to hand

Thanks in advance,
Richard

[MrZack]

Unipolar and bipolar stepper motors are totally different in the way they work.
Unipolar motors have 4 coils that are used individually to make the motor move in the right direction.
Bipolar motors have only 2 coils where you have to control the polarity of both coils to make it turn the right way.
With both methods you can control the power for different stepping, like 1/2 or 1/4 stepping.

So to answer your question.....no, you can't use a unipolar controller or control method with bipolar steppers.
What can be done is, using unipolar steppers with bipolar controllers. You just have to wire the unipolar stepper motor in a bipolar way.

[MrZack]

Hi

I had a second look at your idea, and i have to say its an interesting one
It should work. I'll have to try this out.

The one thing that will probably kill the driver is when pins 1 and 2 are high.
I would use a logic NOT, something like 4069, so this can never happen

You also have to limit the current to max. of 500mA per output because that's the maximum the driver can sink. You could use 2 outputs parallel to get 1A max. sink capability. But then you can only control one motor with one driver.
Another problem i see is sleep mode and stepping.

To use your schematics, without limiting anything, you would have to use a motor that is not using more then 500mA, which will not give you much power. And power is what you need in any CNC project.

This being a nice and interesting idea, i would still go with a bipolar or unipolar stepper driver that can power motors up to 3A or more. They are easy to implement and have all the needed features like micro stepping, sleep mode, overheat protection and it's all in one chip .

[rich200313]

Thanks for the feedback. I have decided to go with a controller found on instructables, but replacing MOSFETs with a dual H-bridge, trouble is it can only supply a maximum of 1A and so i may end up using some form of transistor anyway, not sure yet, and the chances are it will never get past idea stage as with most of my ideas . I would still be interested to know if the schematic above would work so i may give that a go sometime now that i have some diodes to hand.

As for an "all in one" stepper IC do you have any suggestions of a low cost driver. It does not have to be bipolar anymore however as several more printers have been destroyed since my first post and i have managed to find 3 unipolar motors.

Thanks again for your reply.

[MrZack]

There are hundreds of schematics and working ideas that you can find on google about unipolar stepper drivers. If your into microchips like pic or atmel, you can make a driver with which you can control up to 8 motors at the same time .

I went with this one: http://www.hobbycnc.com/products/hob...er-board-kits/
It was a great project and it took me about an hour to put everything together.
I took the 4 motor version and with shipping, payed about 105$. And i have to say, it is worth every penny .
And anyway, getting all the stuff you need to make a good and reliable stepper driver you could, maybe, save about 20% from what this kit casts. Getting it all in one package was worth the 20%

You could also salvage the stepper drivers from printers. They also use the all-in-one package types. They are not so powerful, but could be of use....it depends on the project.

Or if you want to play with your own design and make something new, just post your questions here and we'll just have to make it work