Basic Servo Motor doubt

[puremobi]

Hi,
I bought a Futuba s3003 servo
They say with 20ms delay and range b/w 1-2 ms u can control the rotation.
Should the PWN be continously sent to the motor?..
doubt: if i do,the motor continously rotates till mechanical limits.

i believe 1.5 ms is the mid position.

This is the CODE sample for 1.5 ms
when external input to 3.2 pin of 89c51 is given,i enable the servo..

======================================================
void main()
{
TMOD = 0x01;
TH0 = 0xB1;
TL0 = 0xE0;
EX0=1;
EA = 1;
ET0 = 1;
TR0 = 1;

if(P3_2 == 0)
{
void timer0_0();
}
}

void timer0_0 () interrupt 0
{
if(F0){
F0 = 0;
TH0 = 0xB1; // 20ms
TL0 = 0xE0;
P1_0 = 0;
TF0 = 0;
return;
}
else {
F0 = 1;
TH0 = 0xFA; // 1.5ms
TL0 = 0x24;
P1_0 = 1;
TF0 = 0;
return;
}
}

also i find one more issue..if 2ms is for counter clockwise..the servo still rotates in the same clk wise direction..

 

[duffy]

Yes, 1-2ms on, remainder of the 20ms off, sent continuously, 1.5ms is the center. If it runs to the limits, it means the timing is off. Are you using a 12mhz clock?

 

[puremobi]

hi

hi,
firstly ,thank you very much for the reply...
No i am using 11.0592 MHz..
if i send the pulse continously,how does it stop at ,lets say 90 degrees?..
in my above code...it doesnt stop at 90 degrees.

can u pls clarify this point.." the timing is off"..
does it mean..a 0 pulse should be sent from the microcontroller at all time to the motor?

One more note: the seller told me ..its a 24ms servo..

 

[duffy]

At 11mhz looks like your code is going to deliver a 1.37ms pulse. Shorter pulses = clockwise, looking at the top of the servo, so it is going to be more clockwise. You need to reduce
TH0 = 0xFA; // 1.5ms
TL0 = 0x24;

Also, check the pulse on a scope. Make sure you are sending what you think you are sending.

 

[puremobi]

hi,
i did a try..there is problem..the servo keeps goin to its limits..
this is the code
pls do check..
this is what happens
whenever i insert zero to pin 3.2(variable n)
the servo rotates ,else no rotation.
how can i make it specific..like a defined rotation of 90 degrees?..its not happening here..

==============
void main()
{
TMOD = 0x01;
TH0 = 0xB1;
TL0 = 0xE0;
EX0=1;
EA = 1;
ET0 = 1;
TR0 = 1;
=============
if(n== 0)
{

timer0_0();
}

}


void timer0_0 () interrupt 0
{

if(F0){
F0 = 0;
TH0 = 0xed; //20ms
TL0 = 0xff;
p = 0;
TF0 = 0;
return;
}
else {
F0 = 1;

TH0 = 0xFA; // 1.5ms
TL0 = 0x98;
p = 1;
TF0 = 0;
return;
}
}

 

[puremobi]

pls refresh the page..

 

[duffy]

I see the problem - you have to set up a condition for that port pin INSIDE the timer interrupt. Don't make the timer itself conditional, it just runs continuously.

void main()
{
TMOD = 0x01; 
TH0 = 0xB1;
TL0 = 0xE0;
EX0=1;
EA = 1;
ET0 = 1;
TR0 = 1;
void timer0_0();
}

void timer0_0 () interrupt 0
{
  if(F0){ 
    F0 = 0; 
    TH0 = 0xB1; // 20ms
    TL0 = 0xE0; 
    P1_0 = 0; 
    TF0 = 0; 
    return; 
  }
  else { 
    F0 = 1; 
    P1_0 = 1; 
    TF0 = 0;
    if(P3_2 == 0)
    {
      TH0 = 0xFA; // 1.5ms 
      TL0 = 0x24; 
    }
    else { 
      TH0 = 0xF8; // 2.0ms 
      TL0 = 0x31; 
    }
    return; 
  }
}

Like that. Also, use code tags and indent or I'll kill you.

 

[puremobi]

haha..u cant kill me..but u can try..

Hi again,
I tried the code..this is exactly what happens
Whenever the P3.2 ==0 the servo rotates clockwise,if i give continous zero without a break,the servo rotates clockwise to its limits

there is no counter clockwise rotation(2ms)

am i really missin any basic points here?..will it move anti clockwise in this case(the code above)?

duffy, i have one more file,which mite interest you...pls check it out..
iam gonna get a new breadboard to out this stuff in a day or two..
thanks again..have fun!

=========================
the code in the file is meant to run 8 servos using 89c51.the eg code given inthat is to run the servo in clockwise n anticlockwise upto the extremities w/o any defined timing..i.e.it runs irregularly relative to the timer..

 

[duffy]

If P3.2 == 1, does the servo move at all?

 

[puremobi]

nope..
there is no movement at all..
it only responds when p3.2==0

 

[duffy]

Did you remove the conditional statement on the timer function call?

 

[puremobi]

hi,
yes i had removed..
the timer runs continously.
i guess its supposed to run anti clockwise ..when 3.2 is 1..

what else could be the issue?..

 

[Nigel Goodwin]

If you have a scope, then check the output signal - it should be a pulse between 1mS and 2mS, repeated every 20mS or so (the 20mS doesn't need to be accurate, only the 1-2mS matters.

 

[puremobi]

ok,
i will take it to my univ n check it up..only option i hav.
in keil,there is somethin called..logic view analyser..it shows waveforms from a port pin...any clue abt it?...
i was thinkin of switching to 12Mhz crystal...easy calculations perhaps..

 

[duffy]

Try switching these two TH0/TL0 around -

      TH0 = 0xFA; // 1.5ms 
      TL0 = 0x24; 
    }
    else { 
      TH0 = 0xF8; // 2.0ms 
      TL0 = 0x31;

If everything else is correct, it should at least turn clockwise when p3.2==1. See if that happens.

 

[puremobi]

hi..
sry for the late..
i had tried interchanging..but it din work..it still went clockwise when P3.2 = 0.
i even tried the exact value wrt 11.0592 Mhz..
most prolly my univ opens 2mrw..i will check it up there..
there must be some issue with the 1-2 ms..
if any other options...pls lemme knw...
sam

 

[duffy]

Well, that should tell you something right there. If you did that, it should be loading the OTHER timing variable and P3.2 should work the opposite way.

Try this - remove the conditional statement (the "if" clause) so that it just executes one of the timing variables all the time. Now P3.2 shouldn't make any difference. See what happens.

 

[LALAMALIK]

suezmalik

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