rotate a motor 1 revolution then stop

Projects General Guidance
1

i have this dc 3rpm motor http://www.servocity.com/html/3_rpm_gear_motor.html

as one component of a larger machine i need to rotate a wheel 360 degrees with this motor on a button press then stop and wait for the next button press.

i'm assuming for accuracy (since this is not a servo or stepper motor) i would need to imbed a sensor in the wheel to give an exact posistion. maybe a reed switch and magnet like what is used in a bicycle speedometer.

has anyone used a code to accomplish this? i'm having some trouble getting started code side. up until now I've only taken code examples and adjusted them to suit my needs but i can't seem to find anything that i can even adjust to get this project going.

any tips / advice? google searchs havn't been super helpful thus far. thanks!

2

If you want some accuracy, you need to sense multiple times when a motor turns 360 degrees. A reed switch only senses once. I suggest a photo gate and a disk with periodic notches to sense the rotation of the motor multiple times during the 360 rotation for accuracy. With only one switch you may miss as much as a full turn.

3

To get code started you can just pretend you have a large set of high level functions that solve parts of the problem. Or write the story by means of comments before the code

#define MOTORPIN ??
#define BUTTON ??

void setup()
{
  // For debugging
  Serial.begin(115200);

  // init motor
  pinMode(MOTORPIN, OUTPUT);

  // init button
}

void loop()
{
  if (buttonPressed() == true)
  {
    Serial.Println("button pressed");
    rotateMotor(360);
  }
  Serial.print(".");
}

void rotateMotor(int degrees)
{
  // start the motor
  digitalWrite(MOTORPIN, HIGH);
  // wait until enough degrees rotated

  // stop the motor
  digitalWrite(MOTORPIN, LOW);
}
4

You could use a limit switch to stop the motor, and a momentary seal in bypass for the limit switch controlled by an arduino button setup.

5

robtillaart:
To get code started you can just pretend you have a large set of high level functions that solve parts of the problem. Or write the story by means of comments before the code

I just did that yesterday on a project I posted on exhibition, about the large font on 16*2 display. It's a perfect way for procrastination, you lie to yourself that this is gonna work except you don't have the component that does the actual work, like flux capacitor. XD

I think there is a CSCI model for this type of modelling, top down?

6

hmmmmm this limit switch idea has got me thinking in a new direction.

maybe bypass arduino altogether and go with a limit switch and a 555 chip or 2.

a harware based solution might be a bit easier for me on this one.

7

@liudr

I think there is a CSCI model for this type of modelling, top down?

Yep

8

It's one thing to detect when the wheel has done 360, but how are you going to stop it at that point?

Rob

9

I guess mechanically the switch is in the way of further rotation so unless something is done to turn off the motor, it may damage or overcome ( :cold_sweat:) the switch. Just my experience with limit switches. In any way there won't be room for further turning unless you're turning back.