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[on:]

hey

i was trying to make my bot just turn right using l293d and 2 dc motors at the same position(at junction of a grid)[make the right whell go backward and left wheel go forward]. This is a simple code i came up with but the problem is , my left wheel starts rotating first and my right wheel starts after a lag. plz see if there is anything wrong...
thx in advance!

Code:

int pwm2=6,rt1=11,rt2=12;//right motor
int pwm=9,lt1=1,lt2=2;//left motor

void turn_right();

void setup()
{
  //all pins are made OUTPUT
}

void loop()
{
   turn_right();
}
/************************************
forward means *t1=HIGH and *t2=LOW
*************************************/
void turn_right()
{
  
  digitalWrite(rt1,LOW);//right motor bckward
  digitalWrite(rt2,HIGH);
  digitalWrite(lt1,HIGH);//left motor forward
  digitalWrite(lt2,LOW);
  
  //digitalWrite(pwm2,HIGH);
  //digitalWrite(pwm,HIGH);
  analogWrite(pwm,127);
  analogWrite(pwm2,127);
  
  delay(100);//so that the condition for stopping is not reached before it even starts turning
 while(1)
  {
    if(condition for stopping the turning)//
    return;
  }
  
}

//just read above, turn left and go forward functions will be easy if i figure out turn_right

my question is that in the function turn_right, once i give the command

analogWrite(blahblah_pin,xyz)

does the blahblah_pin keep sending the pwm signal till the rest of the program... ie.. till while(1) condition is dissatisfied?

or do we have to keep calling the turn_right func repeatedly from loop?

[Reply #1 on:]

analogWrite is a one-off - the setting is kept until the next analogWrite

[Reply #2 on:]

so how do i implement pwm with arduino to control two motors simultaneously? can u help me with the code?

[Reply #3 on:]

also if its a one off line.. then my wheels should move alternately..
in my case.. they both move simultaneously but the right wheel starts moving after a lag of about 3-4 secs

[Reply #4 on:]

so how do i implement pwm with arduino to control two motors simultaneously?

Two consecutive "analogWrite"s to different pins.
The execution time between the two writes will (in a mechanical motor scale of things) be miniscule, and you won't notice that the motors don't quite start instantaneously.

[Reply #5 on:]

thats what ive done:

<quote>
analogWrite(pwm,127);
analogWrite(pwm2,127);
</quote>

[Reply #6 on:]

i even tried using just one pwm pin which is connected to both the enable pins of the l293d. still same problem

[Reply #7 on:]

k2s,

Are you using geared motors?

If you are it's possible that you are suffering from backlash from the gears in the gearbox. 3 to 4 seconds is a bit much for backlash but something you can easily check out.

--
Martyn.

[Reply #8 on:]

yes i am using geared motors.. what is backlash and how do i get rid of it?

[Reply #9 on:]

3 or 4 seconds isn't backlash.
It sounds more like your processor is resetting and then restarting.
You may need some decoupling/suppression - have a look at Grumpy Mike's tutorials.

[Reply #10 on:]

i dunno the model specifications.. got it in an iTRIx workshop.. heres a pic if its of any help

http://www.thinklabs.in/resources/wp-content/uploads/2009/06/10-large-300x225.jpg

[Reply #11 on:]

yea i think u may be right.. i found that tutorial...

http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html

ill try and implement it tom morn..

also.. do you think this can be averted by using two batteries? 1 for the arduino and the other for the motors?

[Reply #12 on:]

thank you everyone.. i used two batteries and voila.. its all good..w00t