3 1/2" floppy drive stepper moters

GaryB

Hi,

Am totally new to robotics and microcontrollers. Has anyone used a Stamp 2 to control a· 3 1/2" floppy drive stepper motor? I've got tons of unit and would like to use them for something.

Thanks - Gary

David B

There are a couple of ways you can do it. One is to use either 4 transistors or a transistor array chip to drive each stepper coil, then use four stamp pins to sequence the 4 stepper coils. Another is to buy a controller chip which internally generates the step sequence, then use two stamp pins to generate step and direction controls. Each method has advantages and disadvantages. Lots of people have done this; you can do a Google search for lots of specific chip, circuit and program information.

David

GaryB

David,

I appreciate your response. As I mentioned, I am truly new to this and am just going through the WAM and Boe-bot manuals. I've tried Googleing stepper motors and have found things for the 5 1/4" motors using the parallel port, but nothing on the 3 1/2 motors. Perhaps I'm asking the wrong question.

So, what transistors do you suggest and which controller chip do you suggest. In your opinion, what are the advantages and disadvantages to each are there?

Again, thanks. - Gary

David B

A lot depends on what you want to do with the motor.

I don't know 5 1/4 from 3 1/2 motors. No matter what equipment the motors used to drive, you need to identify the motors as unipolar vs. bipolar and get some idea of what current they will need. So I would suggest to eliminate the 3 1/2 or 5 1/4 from your Google search and focus on searching on basic stepping motors information.

Here is an example site that will tell you way more than I ever could:

http://www.cs.uiowa.edu/~jones/step

The only ex-floppy stepper motors I've used were unipolar, which makes the drivers pretty easy to put together.

If you just want to get started with experimenting with running one from your stamp, it's probably easiest to make up discrete transistor coil drivers. From an educational point of view this also is a good way to get a sense of what is involved in driving a stepper motor.

You only need a few tens of milliamps to run a small motor on your workbench, so almost any general purpose transistor like a 2n3904 or 2n2222 would do the job. Or you could use transistor array chips like the ULN2003, which are nice because they have built-in voltage spike suppression diodes.

Your stamp will need to turn each transistor on and off in the proper sequence to step the motor in either direction.

Using discrete transistors has the advantage that many hobbyists already have adequate transistors in their junkbox, and of being straightforward to modify for higher current if you need it just by changing the transistors. It has the disadvantage of needing 4 driving pins from your CPU and your program having to track the proper bit patterns to send to the motor for each next step.

I've only used the MC3479 stepper driver chip. It has advantages of only needing two driving pins, and it manages the stepper phases for you. It has a disadvantage that each step takes two operations, from my assembly-programming point of view - raising a pin, delaying at least 10 microseconds, then lowering the pin. You may not have that problem if you're using a stamp to generate pulses.

But for now I'd suggest that you read Jones's stepper site for a good introduction to steppers in general.

Have fun!

David