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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.

  • Ensure you use heavy enough wire and connectors that can handle the current.

    Check the voltage getting to the motors and trace it back to the supply, making sure it is good at each intermediate node.

  • 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 dougw

    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 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

    The Pololu site only list 12V and 6 V motors. I assume you are using 12V.  You have found your problem, now you must find the solution. Your circuit is dropping the voltage to 9V with the regulators. I'm not sure the motors will have enough torque at that voltage. You should disconnect the motor from the circuit and connect it directly to the battery. If it runs OK then  connect one directly to the 9V if plenty of torque at that point then maybe the L293's are not supplying the motors correctly.

  • in reply to billpenner

    I'v tried to connect directly to the 12V battery source and it did not change the torque. i think the problem arises from the fact that i get 3.5V at the motors end point and not 9V as what goes out of the regulators. I'll be rechecking tomorrow the voltage at all the hub points and at the end point with different input voltages (12V & 9V) and return with the measured results.

    P.S. The motor type i'm using are the 6V 1.6A at stall: https://www.pololu.com/product/2215

  • 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.