Actions
Forum Thread Details
  • Replies 18 replies
  • Subscribers 393 subscribers
  • Views 3225 views
  • Users 0 members are here
Related

L293D+Arduino+DC motors setup won't deliver enough power to wheels

roineust

Hello,

i'm not getting enough power to the driving wheels on the setup described in the following diagram.

i'v done very similar cuircuits in the past with the exact same components and the driving force from DC motors was much stronger. Can't seem to find what i'm doing wrong..

The DC motors used are these: https://www.pololu.com/product/2215

image

 

Here is the code used:

 

#include <Servo.h>

 

 

#define E 5  // Enable Pin for all motors

 

#define drive_up_left_wheel1 6  // Control pin 1 for motor 1

#define drive_up_left_wheel2 7  // Control pin 2 for motor 1

#define drive_up_right_wheel1 8  // Control pin 1 for motor 2

#define drive_up_right_wheel2 9  // Control pin 2 for motor 2

#define drive_down_right_wheel1 10  // Control pin 1 for motor 3

#define drive_down_right_wheel2 11  // Control pin 2 for motor 3

#define drive_down_left_wheel1 12  // Control pin 1 for motor 4

#define drive_down_left_wheel2 13  // Control pin 2 for motor 4

 

Servo steer_up_left_wheel;

Servo steer_up_right_wheel;

Servo steer_down_right_wheel;

Servo steer_down_left_wheel;

 

void setup() {

 

     set_low_speed();  

 

    attach_steer_servos();

  

    steer_vertical();

  

    drive_down();

  

    delay(6500);

  

    drive_stop();

  

    delay(1000);

     

}

 

void loop() {  

  

    steer_horizontal();

  

    delay(1000);

  

    drive_left();

  

    delay(2500);

  

    drive_stop();

  

    steer_vertical();

  

    delay(1000);

  

    drive_up();

  

    delay(4000);

  

    drive_stop();

  

    steer_horizontal();

  

    delay(1000);

 

    drive_right();

  

    delay(2500);

  

    drive_stop();

  

    steer_vertical();

  

    delay(1000);

  

    drive_down();

  

    delay(3600);

  

    drive_stop(); 

  

}

 

 

void attach_steer_servos(){

 

    steer_up_left_wheel.attach(A1);

    steer_up_right_wheel.attach(A0);

    steer_down_right_wheel.attach(A2);

    steer_down_left_wheel.attach(A3);

  

} 

  

  

void steer_horizontal(){

     

    steer_up_left_wheel.write(48);

    steer_up_right_wheel.write(128);

    steer_down_right_wheel.write(32);

    steer_down_left_wheel.write(154); 

                

}

 

void steer_vertical(){

 

    steer_up_left_wheel.write(144);

    steer_up_right_wheel.write(35);

    steer_down_right_wheel.write(122);

    steer_down_left_wheel.write(66);

  

    delay(500);

                

}

 

void steer_sleight_right(){

     

    steer_up_left_wheel.write(52);

    steer_up_right_wheel.write(134);

    steer_down_right_wheel.write(25);

    steer_down_left_wheel.write(128); 

    

   }

 

void steer_sleight_left(){

     

    steer_up_left_wheel.write(52);

    steer_up_right_wheel.write(134);

    steer_down_right_wheel.write(25);

    steer_down_left_wheel.write(128); 

    

   }

  

void set_medium_high_speed(){

 

  analogWrite(E, 250); // Run in almost full speed

 

}

 

void set_medium_speed(){

 

  analogWrite(E, 195); // Run in half speed

 

}

 

void set_low_speed(){

 

  analogWrite(E, 30);  // Run in low speed

 

}

 

void drive_stop(){

              

    digitalWrite(drive_up_left_wheel1, LOW);

    digitalWrite(drive_up_left_wheel2, LOW);

    digitalWrite(drive_up_right_wheel1, LOW);

    digitalWrite(drive_up_right_wheel2, LOW);

    digitalWrite(drive_down_right_wheel1, LOW);

    digitalWrite(drive_down_right_wheel2, LOW);

    digitalWrite(drive_down_left_wheel1, LOW);

    digitalWrite(drive_down_left_wheel2, LOW);

    

    }  

 

void drive_right(){

  

       digitalWrite(drive_up_left_wheel1, LOW);

       digitalWrite(drive_up_left_wheel2, HIGH);

       digitalWrite(drive_up_right_wheel1, LOW);

       digitalWrite(drive_up_right_wheel2, HIGH);

       digitalWrite(drive_down_right_wheel1, LOW);

       digitalWrite(drive_down_right_wheel2, HIGH);

       digitalWrite(drive_down_left_wheel1, HIGH);

       digitalWrite(drive_down_left_wheel2, LOW);

   

    }

     

void drive_left (){

 

   digitalWrite(drive_up_left_wheel1, HIGH);

   digitalWrite(drive_up_left_wheel2, LOW);

   digitalWrite(drive_up_right_wheel1, HIGH);

   digitalWrite(drive_up_right_wheel2, LOW);

   digitalWrite(drive_down_right_wheel1, HIGH);

   digitalWrite(drive_down_right_wheel2, LOW);

   digitalWrite(drive_down_left_wheel1,LOW);

   digitalWrite(drive_down_left_wheel2, HIGH);

 

}

  

void drive_down (){

 

   digitalWrite(drive_up_left_wheel1, HIGH);

   digitalWrite(drive_up_left_wheel2, LOW);

   digitalWrite(drive_up_right_wheel1, LOW);

   digitalWrite(drive_up_right_wheel2, HIGH);

   digitalWrite(drive_down_right_wheel1, HIGH);

   digitalWrite(drive_down_right_wheel2, LOW);

   digitalWrite(drive_down_left_wheel1,HIGH);

   digitalWrite(drive_down_left_wheel2, LOW);

 

}

 

 

  void drive_up (){

  

   digitalWrite(drive_up_left_wheel1, LOW);

   digitalWrite(drive_up_left_wheel2, HIGH);

   digitalWrite(drive_up_right_wheel1, HIGH);

   digitalWrite(drive_up_right_wheel2, LOW);

   digitalWrite(drive_down_right_wheel1, LOW);

   digitalWrite(drive_down_right_wheel2, HIGH);

   digitalWrite(drive_down_left_wheel1,LOW);

   digitalWrite(drive_down_left_wheel2, HIGH);

 

}

 

 

Any ideas what could be the reason for that problem?

Thanks.

Parents

  • You could require up to near an Amp of current to drive each wheel. That depending upon which motor you are using. Follow Douglas Wong's advice to see if you have full voltage at the motors while power is applied. You may have to modify the program so that voltage is continuously supplied to the "test motor while the voltage is being measured.

  • in reply to billpenner

    I'm getting 3.5V instead of 9V at the motors + and - while they are running. i'll be checking the intermediate points again soon, although i think i already did that and the only intermediate points are before and after the L293D and there i get 9V. The wires are about 1 meter long, but i think not too thin..they don't warm up, that is for sure..

  • in reply to roineust

    If it is being driven with PWM, your meter may not read the voltage accurately. If it is PWM, ensure it is putting out 100% duty cycle.

  • in reply to dougw

    Could the PWM duty cycle be the reason not only for problems in reading the correct voltage, but also for lack of power transfer to the motors?

     

    Do you mean the following function:

     

    void set_low_speed(){

     

      analogWrite(E, 30);  // Run in low speed

     

    }

     

     

    Because when i am referring to low power transfer in comparison to previous configuration with identical components, i mean that i had much more power from motors at LOW speed..

     

    i will add to the list of measurements i have to do, also checking out the voltage when using analogWrite(E, 255);

  • in reply to roineust

    Since you are using 6V motors you should not be using 12V or 9V for the source. you say that the voltage did not change when connected directly to battery? Did the voltage measured at the motor at that time still read 3.6V I suspect that that you are measuring the voltages after being processed by the  Arduino. In which case You are measuring the average voltage which is not DC. you may have to borrow an oscilloscope to see the true results.

  • in reply to roineust

    You say "Because when i am referring to low power transfer in comparison to previous configuration with identical components, i mean that i had much more power from motors at LOW speed." This would seem to indicate that the problem is in the supply source instead of the PWM duty cycle. Again maybe an oscilloscope may be in order.

  • in reply to billpenner

    Here are the results of the measurements, the problem is that in previous configurations, i'm sure i was able to get no dependency between speed and power - i was getting very nice power also at lower speed e.g. analogWrite(E,30), now i'm getting high power only when the speed is also higher and not when the speed is low. I just don't understand what is different: Same type of battery, same type of motors, same length and type of wires, same type of Arduino, same type of L293D chips, same code. This is very confusing.. it is essential for me to get good power at low speed and i'v been there already and unable to get there again.

     

     

    9V (from regulators)analogWrite(E,30);analogWrite(E,255);
    Before L293D~9.0V~9.0V
    After L293D~2.4V~7.6V
    At motors~2.4V~7.4V
    Motor Speed (S) and Power (P)

    S:med-

    P:low

    S:high

    P:high

     

    12V (bypassing regulators)analogWrite(E,30);analogWrite(E,255);
    Before L293D~12.3V~12.3V
    After L293D~4.2V~10.8V
    At motors~4.0V~10.2V
    Motor Speed (S) and Power (P)

    S:med+

    P:low+

    S:high+

    P:high+

     

     

    Do you have an idea what am i doing wrong?

  • in reply to dougw

    Here are the results of the measurements, the problem is that in previous configurations, i'm sure i was able to get no dependency between speed and power - i was getting very nice power also at lower speed e.g. analogWrite(E,30), now i'm getting high power only when the speed is also higher and not when the speed is low. I just don't understand what is different: Same type of battery, same type of motors, same length and type of wires, same type of Arduino, same type of L293D chips, same code. This is very confusing.. it is essential for me to get good power at low speed and i'v been there already and unable to get there again.

     

     

    9V (from regulators)analogWrite(E,30);analogWrite(E,255);
    Before L293D~9.0V~9.0V
    After L293D~2.4V~7.6V
    At motors~2.4V~7.4V
    Motor Speed (S) and Power (P)

    S:med-

    P:low

    S:high

    P:high

     

    12V (bypassing regulators)analogWrite(E,30);analogWrite(E,255);
    Before L293D~12.3V~12.3V
    After L293D~4.2V~10.8V
    At motors~4.0V~10.2V
    Motor Speed (S) and Power (P)

    S:med+

    P:low+

    S:high+

    P:high+

     

     

    Do you have an idea what am i doing wrong?

  • in reply to roineust

    I can offer a theory, but it is just something I have thought about - I never tested it.

    In a normal DC motor torque goes up as speed goes down because the current increases as the back-emf goes down.

    In a stepper motor or PWM drive it is a bit different.

    DC motor torque is proportional to current in the motor.

    The current through the motor is generated by averaging a constant (peak) voltage PWM signal. The motor inductance does not allow instantaneous changes in current, so high frequency PWM just gets "filtered" to an average current. At low duty cycle this becomes a low current, and low torque.

    If you reduce the PWM frequency (but maintain the same PWM duty cycle) the individual pulses will be longer, allowing the current to build up to maximum and thus apply maximum torque during the "on" period.

    If you go too low on the frequency the motor will start to vibrate and buzz or jerk, but you may be able to find a magic frequency where the buzz is acceptable and the peak torque is increased.

    Some of the motors I have used seem to start vibrating when the frequency falls below 300 Hz and the vibration gets pronounced below 200 Hz. You could try running in this frequency range to see if it increases apparent torque.

    What PWM frequency are you running?

  • in reply to dougw

    I don't know what PWM frequency i'm running or what is the duty cycle..

    None of them has to do with the line in the code i'm referring to all the time? which is: analogWrite(E,30); which goes from the Arduino to the L293D enable chips legs??

  • in reply to roineust

    According to the documentation for analogWrite() on the Uno most PWM pins are approximately 490 Hz, pins 5 and 6 are approximately 980 Hz.

  • in reply to roineust

    Hi Roi,

    Do you have flyback protection diodes across the motors. I have seen where the counter EMF if not eliminated can mess with the outputs of the drivers.

    John

Reply Children