Stepper motors are great for (semi-)precise control, perfect for many robot and CNC projects. This motor shield supports up to 2 stepper motors. The library works identically for bi-polar and uni-polar motors
For unipolar motors: to connect up the stepper, first figure out which pins connected to which coil, and which pins are the center taps. If its a 5-wire motor then there will be 1 that is the center tap for both coils. Theres plenty of tutorials online on how to reverse engineer the coils pinout. The center taps should both be connected together to the GND terminal on the motor shield output block. then coil 1 should connect to one motor port (say M1 or M3) and coil 2 should connect to the other motor port (M2 or M4).
For bipolar motors: its just like unipolar motors except theres no 5th wire to connect to ground. The code is exactly the same.
Running a stepper is a little more intricate than running a DC motor but its still very easy
#include <Wire.h> #include <Adafruit_MotorShield.h> #include "utility/Adafruit_PWMServoDriver.h"
Adafruit_MotorShield AFMS = Adafruit_MotorShield();
Adafruit_StepperMotor *myMotor = AFMS.getStepper(200, 2);
...with getStepper(steps, stepper#).
Steps indicates how many steps per revolution the motor has. A 7.5 degree/step motor has 360/7.5 = 48 steps.
Stepper# is which port it is connected to. If you're using M1 and M2, its port 1. If you're using M3 and M4 indicate port 2
Set default speed
Set the speed of the motor using setSpeed(rpm) where rpm is how many revolutions per minute you want the stepper to turn.
Run the motor
Then every time you want the motor to move, call the step(#steps, direction, steptype) procedure. #steps is how many steps you'd like it to take. direction is either FORWARD or BACKWARD and the step type is SINGLE, DOUBLE, INTERLEAVE or MICROSTEP.
- "Single" means single-coil activation
- "Double" means 2 coils are activated at once (for higher torque)
- "Interleave" means that it alternates between single and double to get twice the resolution (but of course its half the speed).
- "Microstepping" is a method where the coils are PWM'd to create smooth motion between steps.
Theres tons of information about the pros and cons of these different stepping methods in the resources page.
You can use whichever stepping method you want, changing it "on the fly" to as you may want minimum power, more torque, or more precision.
By default, the motor will 'hold' the position after its done stepping. If you want to release all the coils, so that it can spin freely, call release()
The stepping commands are 'blocking' and will return once the steps have finished.
Because the stepping commands 'block' - you have to instruct the Stepper motors each time you want them to move. If you want to have more of a 'background task' stepper control, check out AccelStepper library (install similarly to how you did with Adafruit_MotorShield) which has some examples for controlling three steppers simultaneously with varying acceleration
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