Arduino Uno DC-Motor Controller概念澄清

Question

I just started learning Arduino. I thought about going hands on with a Robot which I want to get some autonomy in. I got stuck trying to understand the motor control for the DC motor. I've tried to look up resources but can't find one that adequately explains my problem. I can't understand (being a comp sci undergrad) how or what I am doing wrong writing the code for the motor.

My code just for running the motors for a test is :

// MotorA
int dir1PinA = 7;
int dir2PinA = 5;
int speedPinA = 6;

//motor B

int dir1PinB = 4;
int dir2PinB = 2;
int speedPinB = 3;


void setup() {
  //Serial.begin(9600);
  pinMode (dir1PinA, OUTPUT);
  pinMode (dir2PinA, OUTPUT);
  pinMode (speedPinA,OUTPUT);
  pinMode (dir1PinB, OUTPUT);
  pinMode (dir2PinB, OUTPUT);
  pinMode(speedPinB, OUTPUT);

  // put your setup code here, to run once:

}

void loop() {
  analogWrite(speedPinA, 500);
  analogWrite(speedPinB, 500);
  digitalWrite (dir1PinA, LOW);
  digitalWrite (dir2PinA, HIGH);
  digitalWrite (dir1PinB,HIGH);
  digitalWrite (dir2PinB, LOW);

  // put your main code here, to run repeatedly:

}

I am just trying to run the motor at a certain speed to no avail. I found a sample code that uses the same method to control the motor but has just an extra loop and variable speed .

The test code which works is :

//Motor A
int dir1PinA = 7;
int dir2PinA = 5;
int speedPinA = 6;

//motor B
int dir1PinB = 4;
int dir2PinB = 2;
int speedPinB = 3;

unsigned long time;
int speed;
int dir;

void setup ()
{
pinMode (dir1PinA, OUTPUT);
pinMode (dir2PinA, OUTPUT);
pinMode (speedPinA, OUTPUT);
pinMode (dir1PinB, OUTPUT);
pinMode (dir2PinB, OUTPUT);
pinMode (speedPinB, OUTPUT);
time = millis ();
speed = 0;
dir = 1;
}

void loop ()
{
analogWrite (speedPinA, speed);
analogWrite (speedPinB, 555 - speed);

// set direction
if (1 == dir)
{
digitalWrite (dir1PinA , LOW);
digitalWrite (dir2PinA, HIGH);
digitalWrite (dir1PinB, HIGH);
digitalWrite (dir2PinB, LOW);
}
else
{
digitalWrite (dir1PinA, HIGH);
digitalWrite (dir2PinA, LOW);
digitalWrite (dir1PinB, LOW);
digitalWrite (dir2PinB, HIGH);
}

if (millis () - time> 5000)
{
time = millis ();
speed += 20;
if (speed> 555) {speed = 0;}

if (1 == dir)
{dir = 0;}
else
{dir = 1;}
}
}

Now I understand there are loops and extra variables but theoretically they shouldn't be required to just run a motor at a certain speed. My question is that What am I missing from the top sketch that is in the second one but is absolutely critical to the running of the motor?

I want to apologize in advance if this is a noob moment but I tried and can't find any logic lol.

Answer 1

In the "working" Arduino code ( _{c++ , yes it's compiled by a c++ compiler} ) one of your both motors (B) starts immediately, and the other one 5 sec after reset (or even later)? And the immediately started motor changes direction after 5 sec?

Else, try small modifications to the working sample, towards your simplification, to get some more understanding.
Eg first remove the "dir" change and "else" part

Answer 2

Okay first I will debug your code, I will make a some assumptions about your hardware since you didn't post any photos or schematics, finally I will provide a working solution.

Your Code:

So my first assumption is that your Motor has 3 pins because you're toggling two between high and low, presumably to reverse current, and then one to set the speed.

As I am guessing you know, in order to get a motor to reverse you need to flip the direction the current is going. Setting these pins high and low won't actually reverse the current. Also, the Arduino doesn't really have enough output current to drive a DC motor. You can probably slowly run one. If you want to do more you'll need an external power source.

Drive a DC motor in one direction:

This is probably the easiest one to do. You just need a transistor, diode and resistor. Here is a tutorial

Drive up to four DC motors in both directions

If you want to drive your DC motor in two directions then you need to flip the direction the current is going. This seems complex at first until you realize they've already built something for you to do this exact thing. It's called a Motor Control. It's just a shield with a few H-Bridges on it. They're pretty cheap.

I like AdaFruit's . I have a couple and I built a robot with it not to long ago.

Tutorial on how to use the Adafruit MotorShield