# Stepper Motor Specs

#### Tralfagar

Joined Jun 4, 2007
5
Hello all; I am a proud owner of a Superior Electric Slo-Syn Stepping Motor(yay!). However, I seem to have run into a small roadblock; I don't know how to use it. I notice on the specs it says 1.65V, 4.7A, and it's DC. With that in mind, I have created the following circuit:

It uses an Arduino DueMilaNove, which outputs 5V. I am using it to control a transistor, which will supply current to the motor. I've been doing some reading on the web, and it appears the current is more important than the voltage. I think the values are correct, but

I'm concerned about being able to find a 1 Ohm resistor(never seen one that small), and what can I use for a voltage/current source? I had thought about using 1.5V batteries in series, but is there a better way? I don't think I can drive it straight from the microcontroller....

Thank you. I've tried to find information for the past few days, but it appears I may be missing something obvious

#### Kermit2

Joined Feb 5, 2010
4,162
You will want to remove the small 1.2 Ohm resistor.

According to ohms law that resistor @ 1.65 Volts will limit your current draw through the transistor to less than 2 amps(more than 1 amp).

a better choice for this Might Be a sensitive gate Triac between the motor and several D cells in parallel. You could then PWM the trigger voltage and get a primitive form of variable freq speed control @ the motor. You might even need to use some 2Volt Lead Acid cells instead of the 1.5-1.6 volt dry cells.

#### wayneh

Joined Sep 9, 2010
17,153
I'm concerned about being able to find a 1 Ohm resistor(never seen one that small)
I just bought a bunch of 15W resistors from Mouser, all less than 1.5Ω and most <1Ω. But more importantly, why do think you need it?
, and what can I use for a voltage/current source? I had thought about using 1.5V batteries in series, but is there a better way? I don't think I can drive it straight from the microcontroller....
You're right about that! You need more than 4A, and that's a lot. I'd recommend an old computer PSU. The 5v supply will probably be rated for more than 5A or so. Also, I'd recommend a logic level MOSFET for your transistor, to minimize the "on" resistance and the heat build-up.

You also need to reverse your flyback diode around the motor. Right now it shorts to ground.

#### davebee

Joined Oct 22, 2008
540
Are you sure you have a stepping motor? Usually those have four windings that need to be pulsed on and off in the right sequence to cause the motor shaft to rotate in discrete steps.

The easiest way to drive a stepper motor is to buy a stepping motor control chip which generates the four phased outputs, but it's not that hard to drive one with four separate driver circuits like what you've shown, and then it would be up to your microcontroller program to control four output pins to enable and disable the current to the four windings in the right sequence.

The 4.7A is probably the upper limit. You could probably test-run the motor with no load with just a hundred or so ma.

#### Kermit2

Joined Feb 5, 2010
4,162
That's it Davebee!

This thing was meant for a 3.3V system. Wired Bipolar- Opposite coils in series.

I recently ordered a nice 6A capable PS @ 3.3V from Allied.com. They would be perfect here. Just a hair shy of $22 I think was what it was. A slightly bigger($) one would be preferred for that motor.

#### SgtWookie

Joined Jul 17, 2007
22,221
It would help a great deal if you would supply the complete part number of your stepper motor, as then the datasheet for it can be located.

It is likely that your stepper motor is a 4-wire bipolar type. These have more complicated drive requirements than a unipolar stepper motor, as you need to use a full H-bridge for each winding.

Unipolar stepper motors generally have 5 or 6 wires. One or two of the wires are connected to the center tap(s) of the windings; this gets connected to the positive supply; the ends of the windings get connected to ground in a sequence that makes the motor rotate in the desired direction.

Here is a useful tutorial page with links: http://www.cs.uiowa.edu/~jones/step/
A useful Wikipedia entry: http://en.wikipedia.org/wiki/Stepper_motor

[eta]
Here's an application note on using an L297 stepper motor driver with an L298 H-bridge:
http://us.st.com/stonline/books/pdf/docs/1734.pdf
It's not adequate for the current your motor requires, but it's useful in that you get an idea what kind of control signals are used to drive a bipolar stepper motor.

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