Driving BiPolar Stepper Motors

I can't seem to find the information on this, and i hope that someone can point me in the right direction.

Im using a pca9685 to drive stepper motors, but the maximum output current is just 20ma, and the steppers need a 300ma to run properly.

i can change the pca9685 to another 16bit i/o port expander with a higher current output, but i can only find ones with a high SINK, not supply.

i have however used my rudimentary skills to bash together a transistor system which may be an alternative, but its hopelessly lost!

thanks

You probably want a stepper motor driver like the A4988 to drive
a bipolar stepper.

What are the details of the motor other than 0.3A ? In particular the
winding resistance (is this high or low impedance motor?)

Agreed on the A4988. This one would work very well and it is hard to be the price http://www.pololu.com/product/1182 Furthermore, Pololu gives excellent product support.

MarkT:
You probably want a stepper motor driver like the A4988 to drive
a bipolar stepper.

What are the details of the motor other than 0.3A ? In particular the
winding resistance (is this high or low impedance motor?)

3-5v and 20 Ohm

i need to squash a large amount of these into a small space, so whilst a breakout board isn't feasible, maybe i can find some version of the a4988 with more outputs.

kelvinmead:
I need to squash a large amount of these into a small space, so whilst a breakout board isn't feasible, maybe I can find some version of the a4988 with more outputs.

I think you need to get real. :astonished:

Your first task is to get something that works. If the Pololu breakout (0.6" by 0.8") matches the parameters of your motors, then that is what you need to use.

In any case, you would find it extremely difficult to fit the necessary heatsinks on a smaller area than the Pololu breakout. Oh! Did you not realise you would need heatsinks?

kelvinmead:

MarkT:
You probably want a stepper motor driver like the A4988 to drive
a bipolar stepper.

What are the details of the motor other than 0.3A ? In particular the
winding resistance (is this high or low impedance motor?)

3-5v and 20 Ohm

20 ohms x 0.3A = 6V in my book, anyway 20 ohms is medium impedance - how fast
do you want to drive this motor BTW? chopper drivers like the A4988 are probably
the best bet (the smallest you can get AFAIK, and can cope with 0.3A nicely with
moderate cooling strategy). You only need two wires per motor with such a controller
as its step+directoin.

h-bridge needs 4 transistors per coil.

one pair per wire.

also, one driver per motor. you should not make a practice of trying to use one driver for multiple motors.

MarkT:

kelvinmead:

MarkT:
You probably want a stepper motor driver like the A4988 to drive
a bipolar stepper.

What are the details of the motor other than 0.3A ? In particular the
winding resistance (is this high or low impedance motor?)

3-5v and 20 Ohm

20 ohms x 0.3A = 6V in my book, anyway 20 ohms is medium impedance - how fast
do you want to drive this motor BTW? chopper drivers like the A4988 are probably
the best bet (the smallest you can get AFAIK, and can cope with 0.3A nicely with
moderate cooling strategy). You only need two wires per motor with such a controller
as its step+directoin.

http://www.ebay.co.uk/itm/DC-3-5V-2-Phase-4-Wire-1-1500RPM-6mm-Diameter-Mini-Stepper-Motor-5-Pcs-/291218247501?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item43cdf5cf4d

Specification:

Resistance: 20?
Voltage: 3-5V
When the 4 step angle: 18 °
Package Including
6mm Canon micro-step motor

http://www.ebay.co.uk/itm/10x-2-phase-4-wire-stepper-motor-MCU-learning-Board-6mm-Canon-micro-step-motor-/161152765264?pt=UK_BOI_Industrial_Automation_Control_ET&hash=item2585740d50

EDIT apologies, the original listing i bought them from doesn't exist anymore, and there was less info than this.

I did buy 100 for £14 though, and they are retailing here for £2 odd each!