Let's Make Robots!

Arduino Object Avoidance with PING and Hacked RC Car

 

Finished Bot Here: http://letsmakerobots.com/node/26101

Before I begin I am a Senior Electrical Engineer student in college. This is a project im working on for my design class. I am very new to arduino and its language. Having said that here we go:

Working on an object avoiding vehicle using Arduino and Ping ultrasound sensor. I hacked an old rc car. Basically removed all the guts and replaced it with a breadboard and the arduino. I am still using the 9V rechargeable battery pack that came with the car to power the 2 motors through an L293D chip and a regular 9v battery to power the arduino. When I turn on the robot it runs well and responds while im holding it in the air so the code seems to be working. But then things go bad. Here are the issues i've come across so far.

After a while it begins to slow down and stop as you can see in the video. Battery is charged

When changing directions it badly stutters. will post another video soon showing this.

Not enough torque to run on carpet. Runs on tile but slows to a stop when changing directions.

When I grab one wheel to stop it while its running the other slows and eventually stops. Not too much of an issue there but just wondering why it happens since they are running independantly? gueesing it has to do with the overheating of the L293D.

I left the original two capacitors going across the motors attached, tried removing them and had same issue so I put them back. Also the L293D (can handle 0.6 amps) chip gets VERY hot while its running and starts to smell like its burning. I ordered a chip called  ‘SN754410‘ from Texas Instruments. It can handle double the current of the L293D and has the same pin layout. It comes in next week so hopefully that will make a difference. Will update when it comes

I have the PING sensor mounted on a servo. After these issues are addressed I would like to add a section to the code to allow the servo to pan while its driving so it will avoid it from running into anything at any angle OR when it comes to an object look left and right and choose the best direction. I am horrible at code writing so any links to similar codes I can use or if anyone can help would be greatly appreciated.


Will post more pictures and videos as soon as I can.

L293D Chip Layout

Heres how I connected everything: PINS

1 to pin 9 on Arduino board, 2 to pin 3 on Arduino board, 3 to motor1 (either + or -) it wont matter as its DC, 4 to the gnd rail on the breadboard, 5 to the gnd rail on the breadboard, 6 to motor1, 7 to pin 4 Arduino, 8 to power (+) rail., 9 to pin 10 Arduino, 10 to pin 5 Arduino, 11 to motor2, 12 to GND rail, 13 to GND rail, 14 to motor2, 15 to pin 6 Arduino, 16 to power (+) rail

 

 

 

 

Heres the code I used. Credit to @lucky_larry on twitter for most of the code. I made a few changes to allow it to work for my PING sensor. The original was written for the SRF05 ultrasound sensor.

 

#include <Ping.h>

const int numOfReadings = 10;                   // number of readings to take/ items in the array

 int readings[numOfReadings];                    // stores the distance readings in an array

int arrayIndex = 0;                             // arrayIndex of the current item in the array

int total = 0;                                  // stores the cumlative total

int averageDistance = 0;                        // stores the average value

// setup pins and variables for SRF05 sonar device

const int pingpin = 12;                         // ping pin (digital 12)

unsigned long pulseTime = 0;                    // stores the pulse in Micro Seconds

unsigned long distance = 0;                     // variable for storing the distance (cm)

int motor1Pin1 = 3;                             // pin 2 on L293D

int motor1Pin2 = 4;                             // pin 7 on L293D

int enable1Pin = 9;                             // pin 1 on L293D

int motor2Pin1 = 5;                             // pin 10 on L293D

int motor2Pin2 = 6;                             // pin  15 on L293D

int enable2Pin = 10;                            // pin 9 on L293D

void setup() {

  // set the motor pins as outputs:

   Serial.begin(9600);

  pinMode(motor1Pin1, OUTPUT);

  pinMode(motor1Pin2, OUTPUT);

  pinMode(enable1Pin, OUTPUT);

  pinMode(motor2Pin1, OUTPUT);

  pinMode(motor2Pin2, OUTPUT);

  pinMode(enable2Pin, OUTPUT);

  // set enablePins high so that motor can turn on:

  digitalWrite(enable1Pin, HIGH);

  digitalWrite(enable2Pin, HIGH);

  pinMode(pingpin, OUTPUT);                     

  pinMode(pingpin, INPUT);                      

  // create array loop to iterate over every item in the array

  for (int thisReading = 0; thisReading < numOfReadings; thisReading++) {

    readings[thisReading] = 0;

  }

}

void loop() {

  pinMode(pingpin, OUTPUT);

  digitalWrite(pingpin, HIGH);                  // send 10 microsecond pulse

  delayMicroseconds(10);                        // wait 10 microseconds before turning off

  digitalWrite(pingpin, LOW);                   // stop sending the pulse

  pinMode(pingpin, INPUT);

  pulseTime = pulseIn(pingpin, HIGH);           // Look for a return pulse, it should be high as the pulse goes low-high-low

  distance = pulseTime/58;                      // Distance = pulse time / 58 to convert to cm.

  total= total - readings[arrayIndex];          // subtract the last distance

  readings[arrayIndex] = distance;              // add distance reading to array

  total= total + readings[arrayIndex];          // add the reading to the total

  arrayIndex = arrayIndex + 1;                  // go to the next item in the array

  // At the end of the array (10 items) then start again

  if (arrayIndex >= numOfReadings)  {

    arrayIndex = 0;

  }

  averageDistance = total / numOfReadings;      // calculate the average distance

  delay(10);

  // check the average distance and move accordingly

  if (averageDistance <= 10){

    // go backwards

    digitalWrite(motor1Pin1, HIGH);

    digitalWrite(motor1Pin2, LOW);

    digitalWrite(motor2Pin1, HIGH);

    digitalWrite(motor2Pin2, LOW);

  }

  if (averageDistance <= 25 && averageDistance > 10) {

    // turn

    digitalWrite(motor1Pin1, HIGH);

    digitalWrite(motor1Pin2, LOW);

    digitalWrite(motor2Pin1, LOW);

    digitalWrite(motor2Pin2, HIGH);

  }

  if (averageDistance > 25)   {

    // go forward

    digitalWrite(motor1Pin1, LOW);

    digitalWrite(motor1Pin2, HIGH);

    digitalWrite(motor2Pin1, LOW);

    digitalWrite(motor2Pin2, HIGH);

  }

}

Any comments, help, ideas or input is definately welcome. I also hope this can be used to help someone who is also having similar issues. 

 

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I have exact same problems with my RC car driving of L293D. Exact same thing - to little power, jitters at times etc. Did SN754410 help? What is the current status? Did you fix the motor power problem?

Hey,

I made an updated post at http://letsmakerobots.com/node/26101 check it out.. adressed most of the issues there. Let me know if any other questions

My problem was easely fixed. Turned out I didnt supply enough power. Did you stall the motor and checked the current? My car requires 0.24A per motor and is so powerful that it does a flip when driving against the wall. It cant be your motor actually require more power. I can be wrong, go ahead and check the current, Iam very interested what comes out

I dont have a multimeter handy so I basically  made this bot on trial and error.. The motors r pretty big and i did have to stack 4 chips to get them running right so It would make sense if they required a few amps each. Mine is powerful too. Goes CRAZY propelling itself in the air smashing into things at top speed. had to pwm it down to 60/255 speed. Do you have any pics/video of yours? would like to see it in action.

I dont have any videos but I will add my robot to the list in the next days making videos etc. For now you can check my problems / questions about the robot here:

http://letsmakerobots.com/node/26220

Here a foto:

Arduino is missing because I did some measurments on the motor and was astound that this baby draws jawdropping 5A per motor! 

 

 

note: you can put the 2 outputs from the L93D in parallel, so it can handle twice the current. Offcourse you w'll need 2 l293D's. Look into the datasheet of it for a schematic how to connect. I succesfully tested with a L298n to handle 4 amp's instead of 2.

That  R/C vehicle you picked is made for speed and spins. The tires are not flat, they have a gradual angle on them that will cause the thing to do flips and stunts. I tried the exact same thing t using a pic micro and two wisker switches. It worked great as long as the wheels weren't touching anything. But put it on the ground, and it would either plow into the wall full force, damaging the wall and itself, or flip up on its side. I used the original circuit board that came with the toy because it already had the correct size transistors on it for the motor. I just cut the traces going to the drive chip. If you want to use this for your project, pwm is the only way to go! As far as dragging the front wheels around, those massive rear wheels will have no problem, even on carpet, if you size your h-bridge properly. If you want to see some video of mine being self destructive, I can post it.

Another thing to consider is the speed this thing is going to move. Those are some big wheels, and they are turning fast (or at least they will with the proper h-bridge driving them). There is a good chance that you will be driving towards obstacles faster than you can detect and react to them. It's like driving too fast in your car at night... you can go fast enough that you can't react to something in time, once you see it in your headlights.

For this reason, you should consider using Pulse Width Modulation (PWM) to run the motors at less than full speed. With experimentation, you will be able to determine how fast you can go and still stay within your sensor's speed.

Good luck.