Bipolar Step Motor Driver

This is the wiki page for the Stepper Drivers that TP was working on.

This project was a sub-project of the (still active) DIY CNC Router project, but is no longer itself active.

Overview

I have been tasked with exploring the control of a 4-wire bipolar stepper motor for the DIY CNC Router project.

Background

Being a form of brushless motor, stepper motors require that their windings are charged in a particular sequence with particular polarities. A motor driver is an electronic device that uses logic signals from a controller to connect the winding(s) of a motor to a power supply. The logic signals from the controller determine how and when connections are made, although some drivers simplify the interface out to the controller to only step (frequency controls speed) and direction (CW or CCW). For the 50Ω bipolar stepper motors we need to drive, this boils down to two full H-bridges that can handle 12V with current spikes up to 2A, with an emphasis on minimum component count.

Phase I

Control our 4-wire NEMA17 bipolar test motor with an Arduino using an EasyDriver board from Sparkfun. The EasyDriver board can drive one (1) stepper motor.

The EasyDriver board is being used for this control exercise because:

• Jim already has one
• It has a connection cable soldered to it that matches our test motor
• It is cheaper than other ready-made alternatives suggested so far

Phase II

Attempt to build a low cost driver board and run this driver with an Arduino.

The EasyDriver boards cost about $15 each (plus S&H). I'll be trying to design a board that can be built for less than $30 to drive all the motors we need for the project. The hope is to design something that can be incorporated into a kit we can call our own while being reasonable for another Hackerspace to use or even replicate from scratch.

A secondary design restraint is to make the custom board a drop-in replacement for the EasyDriver boards, so someone trying to build our CNC can use either without software changes. Unfortunately, there will be one major difference: the Phase II driver will full-step whereas the EasyDriver micro-steps. Hopefully this is only a minor software change, like a configuration setting.

Phase III

If the home grown driver is green-lighted by DIY CNC Router team, build soldered board and then test driving and controlling actual project motors with an Arduino controller.

Code

Phase I (Arduino)

Current Status - Inactive

With so many low cost options availble on the market, the desire for completing this project has waned considerably.

Phase I

• Completed, demo'd Oct 20, 2009 at weekly meeting
  • We discovered EasyDriver "micro-steps" motors, which may not be the greatest thing

Phase II

• Basic circuit planned out
• Waiting for parts

Phase III

Work Log

Oct 7, 2009

• Connector (good enough) repaired. Used a #5 jeweler screwdriver to remove pin clamp and re-attached it to wire. Clamp damaged by whatever original event damaged the cable (I received it damaged), so not 100% clamped. Solid enough for use as long as not further abused. I took a picture of the clamp out of the connector, to be posted another time.
• Arduino on order.
  • Software IDE downloaded and unzipped (man it's huge!)
  • Rough draft of exerise software written
    • Since this is just a 'make it turn' exercise, the plan is to use a potentiometer for control: the more the pot is turned left, the faster the motor turns to the left, etc.
• Also ordered some cheap $1 hall-effect sensors (four) which could possibly be of use to the DIY CNC Router project at some point.

Oct 20, 2009

• Demo'd Phase I for Jim and Paul.
  • The connector broke again when I went to dissconnect it from motor.  :(
• Jim and Dave have put together a 4 motor test stand - very cool
  • Dave is taking lead on EasyDrivers now, so I am moving on to Phase II

Current Issues

• Waiting on part order

Next Steps

• I have a $5 H-Bridge chip coming with an order I made for my RC car that has not been dedicated to anything; I ordered it 'just because' - too bad I only got one. I think it is rated for 5A. I'll get some more after doing a proof of concept.

Links of Interest

• http://www.schmalzhaus.com/EasyDriverQuad/index.html