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Topic: I can't get sevo to work right (Read 6549 times) previous topic - next topic

zoomkat

Quote
don't think the arduino can handle continous rotation on a servo.


Sure it does. You just need to understand how they work. I have two continous rotation servos and my code controls them without issue. Often people have issues with their servos due to inadequate power supplies. How is your servo powered? Below is a recomended setup using an external power supply.

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retrolefty

#16
Jun 22, 2011, 02:47 am Last Edit: Jun 22, 2011, 02:58 am by retrolefty Reason: 1
Ok here are the key things to utilise from your basic program to arudino code:

Quote

Stamp uses:
SDelay    Con 15    ' 10 millisecond delay for Servo
Mstop     Con 150   ' Brake Servo
MfFor     Con 200   ' Run Servo Foward Fast
MsFor     Con 160   ' Run Servo Forward Slow
MfRev     Con 80    ' Run Servo Reverse Fast
MsRev     Con 140   ' Run Servo Reverse Slow

Arduino would use:

#define Mstop  1500  // Brake Servo
#define MfFor  2000  // Run Servo Foward Fast
#define MsFor  1600  // Run Servo Forward Slow
#define MfRev  800   // Run Servo Reverse Fast
#define MsRev  1400 // Run Servo Reverse Slow
#define SDelay  2000    // 2 second delay for Servo

And where your stamp program uses:


forward:
debug "Forward",cr
for x=1 to 200
pulsout 0,mffor
pulsout 1,mffor
pause sdelay
next
return

// and

Brake:
debug "Brake",cr
for z=1 to 1000
pulsout 0,mStop
pulsout 1,mStop
pause sdelay
next
return



your arduino code would use:

void forward(void)
{
  Serial.println("Forward");
  myservo.writeMicroseconds(MfFor);
  delay(SDelay);  // delay for 2 secs
}

// and


void Brake(void)
{
   Serial.println("Break");
   myservo.writeMicroseconds(Mstop);
   delay(SDelay * 5); //delay for 10 sec
}



Certainly not a complete sketch, and probably not the best use of the C syntex, but it's more to show a simple conversion from basic to C equivelent.  It shows the critical servo statment and constant values to duplicate what your basic stamp program uses. Hope that's enough to get you headed in the right direction. Now after having to read a basic program I feel kind of dirty and need to go take a shower.  :D

Lefty

oldPGMguy

thanks RETROLEFTY

here is the code i came up with as a test it works.......

Code: [Select]

#include <Servo.h>

Servo myservo;
int pos;
int x;

void forward(){
pos = 2000;  // use 1000 or 2000 for forward or backward
  myservo.writeMicroseconds(pos);  // servo forward
delay(15);
}

void reverse(){
pos = 1000;  // use 1000 or 2000 for forward or backward
  myservo.writeMicroseconds(pos);  // servo forward
delay(15);
}


void servoStop(){
pos = 1500;  // use 1000 or 2000 for forward or backward
  myservo.writeMicroseconds(pos);  // servo forward
delay(15);
}

void setup()
{
   myservo.attach(9);

}

void loop() {
for(x=0; x<1000; x++){
  forward(); }

for(x=0; x<1000; x++){
  servoStop(); }

for(x=0; x<1000; x++){
  reverse(); }
  }


retrolefty

Quote
here is the code i came up with as a test it works.......


Great, you got the idea. The arduino servo library code is automatically handling (and hiding from you) a lot of the stuff that the stamp code had to deal with.

See we can help you 'unlearn' all that nasty BASIC stuff and help you on the journey to learning a real programming language.  ;)

Lefty

oldPGMguy

Hey..i want to learn C....RetroLefty.....thanks to all...for the help

PaulS

The servo library has two functions to send data to a servo - write() and writeMicroseconds(). Continuous rotation "servos" are generally commanded using writeMicroseconds().

The values for writeMicroseconds() generally range from about 500 to about 2500. The lowest value causes fastest speed in one direction. As the values get larger, the speed gets smaller. At some point, around 1500, the "servo" stops altogether. As the values continue to increase, the direction changes, and the servo moves slowly in the other direction, increasing speed up to the upper limit.

Try a loop that calls Servo::writeMicroseconds() with values from 500 to 2500, in steps of 100, with a 1 second delay between calls.
The art of getting good answers lies in asking good questions.

oldPGMguy

ok here's what i came up with......it works great

Code: [Select]
// Continous Rotation Servo Test
// By Herman O Darr (OldElectroGuy)
// June 12 2011
// Revised June 25 2011
// Use Numbers between 0 to 180...90 is usually stop
// Adjust for your servo's using the pot adjust,if installed
// this is for continous rotating servo's...not standard
// servo's from 0 to 180 degree's rotation only



//----------------------- Include's -------------------------

#include <Servo.h>

//------------------------ Variables -------------------------

Servo servo;             // Define servo

//-------------------------- Setup ----------------------------
void setup() {
    servo.attach(9);     // Set servo to digital pin 9
}
//----------------------- Main Loop ------------------------

void loop() {            // Loop through motion tests
  forward();           
  stopRobot();
  reverseslow();
  stopRobot();
  forwardslow();
  stopRobot();
  reverse();
  stopRobot();
}
//------------------------ Sub Voids ------------------------


     // Motion routines for forward, reverse, slow, and stop
void forward() {
   servo.write(0);delay(6000);   }

void reverse() {
  servo.write(180);delay(6000);    }

void stopRobot() {
   servo.write(90);delay(5000);    }
   
void forwardslow() {
   servo.write(88);delay(6000);   }
   
void reverseslow() {
   servo.write(92);delay(6000);   }   

oldPGMguy

@PaulS....yeah i did that with 1000 being forward and 2000 being reverse and 1500 being stop......if you have servo's with an adjustable pot you can set the stop with what ever number yo use....thanks for the info code

gelfling6

It also depends on ho the Constant Rotation servos are wired.. Even though I saw a plan for converting standard servos to C-R type, using 2x 2.2K resistors wired in series, across the old POT pins, with the center bridge to the wiper solder point, I never liked the idea of sloppy tolerance on the resistors. (and, isn't 2.2K a bit low? I thought the POTs were closer to 10K end to end?)

I've done this with modified HiTec & Futaba servos, grinding down the stop tab, and replacing the POT with a mini PC mount 10K, accessible through a side hole... Even replaced the two C-R servos on an old BOE-Bot that the motors had begun screaming.

The servo code works with the VEX Motor modules (essentially Futababa servos with the post ground down, and a square key in the center, but with a custom chip for the driver).

Unlike the VEX controller code to motors, there is no constant pulse going to the signal pins, just for the brief moment you digitalwrite to the pin, or servowrite to the pin.. Once you finish that instruction, the servo would stop anyways, because you are no-longer sending the pulses to it. just a dead GND signal.  Same goes with the Basic Stamp, once you write the pulsout, there is no constant signal.. the delay, just gives the code time to stop, while the servo performs the movement, then waits for the next pulse. (with the VEX, if you wrote out to the motors, the 2nd PIC inside would maintain the pulses, until you told it to stop, which lead to a lot of run-away problems if the code crashed.)


mem


Unlike the VEX controller code to motors, there is no constant pulse going to the signal pins, just for the brief moment you digitalwrite to the pin, or servowrite to the pin.. Once you finish that instruction, the servo would stop anyways, because you are no-longer sending the pulses to it. just a dead GND signal.  Same goes with the Basic Stamp, once you write the pulsout, there is no constant signal.. the delay, just gives the code time to stop, while the servo performs the movement, then waits for the next pulse. (with the VEX, if you wrote out to the motors, the 2nd PIC inside would maintain the pulses, until you told it to stop, which lead to a lot of run-away problems if the code crashed.)


The Arduino Servo library is constantly sending pulses to the servos (every 20ms) without requiring any attention from the sketch.
You only need to write a new values when you want to change the angle, or as in this application, speed.

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