X27.168 Stepper to Speedometer

[matt_funder27]

I am attempting to retrofit a X27.168 stepper motor within an old mechanical speedometer for an engine swap that will now have a VSS.

Currently I am using the AccelStepper Library, and have not been satisfied with what I have been able to accomplish.

First question is there a way around defining the current position ? Any time I upload code it effectively starts from what ever position the motor is in and that is no longer 0 mph.

How do I determine appropriate Speed and Acceleration? The stepper library had the motor running smoother, so I do not believe I have these calibrated accurately.

Once I have these two items addressed, what function would be best for the VSS input ? The moveTo just moves a set number of steps from its current position.

#include <AccelStepper.h>

// Define the stepper motor and the pins that is connected to
AccelStepper stepper1(8, 4, 5, 6, 7); // (Typeof driver: with 2 pins, STEP, DIR)

void setup() {

  stepper1.setMaxSpeed(1500); // Set maximum speed value for the stepper
  stepper1.setAcceleration(1500); // Set acceleration value for the stepper
  stepper1.setCurrentPosition(0); // Set the current position to 0 steps

}

void loop() {
delay(500);
 stepper1.moveTo(-100); // Set desired move: 800 steps (in quater-step resolution that's one rotation)
  stepper1.runToPosition(); // Moves the motor to target position w/ acceleration/ deceleration and it blocks until is in position


  // Move back to position 0, using run() which is non-blocking - both motors will move at the same time
  stepper1.moveTo(0);

  while (stepper1.currentPosition() != 0 ) {
    stepper1.run();  // Move or step the motor implementing accelerations and decelerations to achieve the target position. Non-blocking function

    //
    //
  }
}

[jremington]

To use the X27.168 stepper effectively at maximum resolution, a special pulse sequence is required. You can find articles and Arduino libraries on line that go into the details, including here in this very forum. Very handy guide here.

In general, steppers have to be "homed" at startup. Most people drive them until a limit switch or end stop is reached, call that zero and then go about their business.

It does not damage a stepper motor to stall it, e.g. by driving into an end stop.