discrete stepper motor driver

Go To Last Post
6 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I scavenged a small stepper motor from a broken scanner and would like, as a matter of learning and discovery, to create a simple discrete-component driver for it.

My searching has come up with no promising ideas. I've looked up the datasheets for motors that _seem_ similar on DigiKey, and wired it likewise, but the circuit combined with the activation sequence of the different windings just makes it vibrate and hum. If I drive just two of the coils -- like yellow and orange -- it moves, but has almost zero torque, drawing ~15mA.

The motor has 5 wires: a common red wire (common ground?) with 26.6 ohm resistance to the others. The others are black, brown, yellow and orange.

It has little detent torque, but has nice holding torque when connected directly to 6V.

I'd like to control it with four pins from an AVR running at 5V, in a dual-power rail setup to understand how to do that.

Can anyone direct me to a simple transistor-based design so that I can get it running and measure its characteristics while running, to gain an understanding of what's going on?

This topic has a solution.
Last Edited: Sat. Jan 7, 2017 - 10:44 PM
This reply has been marked as the solution. 
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

The first stop is to find "Jones on steppers"... http://www.divms.uiowa.edu/~jone...

That will help you to understand your wires, give you more links, etc.

Finding prior discussions here that reference Jones may also give other good links.

If it is a tiny stepper then a no-load test rig can be made directly from the AVR--there is an Atmel app note on that.

For any real stepper work, we've used Allegro driver chips to do the hard stuff.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Thanks, that URL looks promising.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

So I used the Jones article to rig up a simple NPN driver for each of the four windings... great. Drawing the right amount of current, transistor biased properly. Can sequence forward and backward. Only problem now is, going both forward and backward, I have a small problem with step size....

Two of the movements are half the size of the other two. I even glues a little pointer on the attached pinion to check it accurately. For s = small and l = large, it goes "slsl." I haven't yet come up with an arrangement or sequence that gives me four steps of the same size, using all four wires, nor have I seen mention of anything like this in the Jones (or related) articles.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Maybe it's broken and is that the reason the scanner was binned :)

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I'd say your sequence is a combination of full/half steps.

The problem obviously lies in line 47. :roll:

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.