help with stepper motor position control

Hi, I am new to this forum.

I am after some help wiring up a stepper motor position controller. I am not even sure if it is possible.. any help would be greatly appreciated.

I have a 6 wire stepper motor.

yellow - common
blue - coil1
white - coil 2

yellow/bk - common
orange - coil 3
red - coil 4

(resistance across each coil is arount 16 ohms)

I need to run it on 12vdc

i need to be able to control position via a potentiometer or something similar through 2.5 turns (900 degrees)

is there a way of doing this?

thanks in advance for your help

G'day mate,
Any microcontroller-based stepper-controller should be able to do that just by counting steps ..
For example, if you have 200 full steps per revolution (1.8deg/step) the controller has to be programmed to assign 500 steps to 2.5 turns of a (multi-turn)potentiometer ..
In other words, 0-5V (or whatever span you choose) is translated to 500 steps, what gives you roughly 10mV/step ..

In practical realization you will need a memory (eg. EEProm) to remember the count of steps, so if the power fails the controller "knows" exactly where it was before ..

Rgds,
IanP

Your simplest solution would be to wire the motor common wires together and to the supply line, then sequence the other wires to ground in order to achieve rotation.

Converting the potentiometer voltage to a position is also easy as IanP stated. Your biggest problem is getting the two to synchronize. At the point where the power is first applied, there is no way for the controlling processor to know the motor angle as there is no feedback mechanism. It would be pointless for example, if the control was set at 90% and you only had 10% range left or if the motor suddenly jumped when the power was turned on.

There are two solutions to this problem, one is to memorize the voltage and motor position every time it moves so you know where it is from a fresh start, the other is to drive the motor to a 'home' position at start-up by rotating it sufficiently that it is guaranteed to hit a stop or at least a position sensor, then count steps up to the desired position.

There are pros and cons to both methods but bear in mind that the memory method assumes that the motor and potentiometer are stationary when the power is turned off and the most motors go 'slack' without power.

Brian.

If potentiometer position feedback is suitable for your application, then more simple drive methods than stepper motor,
particularly DC motor, should be considered.

Nearly all existing stepper driven designs are counting steps and using an index sensor (zero position), if absolute
positioning is required.

Thanks for the replies, having it rotate back to a index point(solid stop) upon start up would work perfectly in this application.

I thought that I might also add that a potentiometer is not 100% necessary as it does not need to be infinately variable. I am looking for perhaps 8 to 12 positions (maybe at 10 90% intervals??) spread evenly throughout the 900%,
would that make it simpler?