Controlling Servo Speed

Projects Programming
1

I've created a Arduino sketch using an HW-201 IR Sensor and a Micro Servo Motor. I'm able to control the speed of the servo to go from 0 to 90 degrees once the Sensor detects and object. I can also control the amount of time it the servo stays at 90 degrees before returning to 0 degrees.
But I can't seem to control the speed for the return of the Servo back to 0 degrees. Can anyone tell me where I've gone wrong with this sketch? I get no compiling errors and it uploads to the Arduino Uno board with no issues. I've tried for a week changing and altering different parts but still no luck. HELP Please.

#include <Servo.h>

Servo servo;
const int analogInPin = A0;
int val=0;               
int servoPin=9;
int angle=90;



void setup() {
servo.attach(servoPin);
}

void loop() {
  val = analogRead(analogInPin);   // This reads the value of the sensor to see if an object is detected. Then saved in the val variable.          
 
  if(val < 600)
  {
  for (angle = 90; angle < 180; angle += 1)
  {
    servo.write(angle);
    delay(6);               // This controls the speed of the Servo (gate) opening. Lower# lower speed.
  }

  delay(3000);               // Sets the delay time. 3000 means the Servo (gate) stays open for 3 seconds before returning.

    for (angle = 0; angle < 90; angle += 1)
    {
    servo.write(angle);     // If object detected the Servo rotates to 90 degrees.
    delay(1);               // This controls the speed of the Servo (gate) returning. Lower# lower speed.
    }                   
}

}
2

this seems like the right approach. have you tried larger delay values? 90 6 msec steps is on ~half a second. and don't you want to used the same delay in both cases?

3

Neither of the for loops in the sketch that you posted move the servo to an angle of 0 degrees

    for (angle = 90; angle < 180; angle += 1)

    for (angle = 0; angle < 90; angle += 1)

Did you post the correct sketch ?

4

The code is exactly as I have wrote it. If I remove the either code for (angle = 90; angle < 180; angle += 1) the servo does not rotate.

5

The delay value for the Servo to go from 0 to 90 works fine with any value I type.
The issue seems to be the delay in the last part of the sketch. This number messes up the servo return and or no speed control.

6

you mean in the above "part of the sketch"?
delay(1) seems kinda fast and may not be guaranteed to even be 1 if the resolution is +/-1.
what does is do with the same value in the other "part"?

7

The delay(6) section operates the servo correctly. A lower number apparently speeds up the rotation.
The delay(1) section has no effect on the servo speed but if I change the number from to 6 to be the same as both sections, the servo over rotates before returning to original position and still no speed control. I used to have a lot of hair.... but now I'm almost bald from pulling my hair out. I know there is an error in there I just don't know where.

8

you have a 3 sec delay "after" moving the servo to 90 deg but no delay "after" rotating it to zero, so it immediately repeats the upper part of the code

9

Greg, the 3 second delay works perfectly and after 3 seconds the servo will return to 0 degrees again but I still have no control of the returning speed. Even though the sketch code line says ......

delay(2) it doesn't seem to have any effect. If I change it to delay(1); no speed changes but still returns to original position after the 3 second delay. If I change the delay(2); to a 5 then the servo over rotates a few degrees before coming back to 0 its original position. I believe the error is somewhere in else other than in these delay settings. I just can't figure it out.
Greg... I appreciate your help so very much but if you want to leave it for now I understand.

10

i didn't notice this before but you first rotate the servo from 90 to 180 and the lower part from 0 to 90. i had assumed the lower part just moves form 180 back to 90.

is the movement to zero what you mean by over-rotates?

11

Yes, that's correct.

12

Then change the loop to go from 180 to 90. You will have to count backwards:

    for (angle = 180; angle > 90; angle -= 1)
    {
    servo.write(angle);     // If object detected the Servo rotates to 90 degrees.
    delay(6);               // This controls the speed of the Servo (gate) returning. Lower# lower speed.
    }

This should go back from 180 to 90 at the same speed as the move from 90 to 180.

13

If you wrote:

for (angle; angle > 90; angle -= 1)
    {
    servo.write(angle);     // If object detected the Servo rotates to 90 degrees.
    delay(6);               // This controls the speed of the Servo (gate) returning. Lower# lower speed.
    }

Would the for loop not start at the current value of angle? I don't have a servo handy at the moment to try.

14

Yes, but since we know the current value is 180 it is clearer to specify.

The "(angle;" part does nothing so a more proper version would be:
for ( ; angle > 90; angle -= 1)

15

Thanks.

16

consider following which uses a sub-function to increment the servo angle from the previous position

#undef MyHW
#ifdef MyHW
struct Servo {
    Servo (void)       { }
    void attach (int pin)  { }
    void write  (int ang)  { Serial.println (ang); }
};

#else
# include <Servo.h>
#endif

Servo servo;

const int analogInPin = A0;

int val=0;
int servoPin = 9;
int angle=90;

// -----------------------------------------------------------------------------
void
servoAng (
    int            ang,
    unsigned long  msec )
{
    static int angLst;

    int dir = ang > angLst ? 1 : -1;

    for ( ; ang != angLst; angLst += dir)  {
        servo.write (angLst);
        delay (msec);
    }
    servo.write (angLst);
}

// -----------------------------------------------------------------------------
void loop() {
    int val = analogRead(analogInPin);   // This reads the value of the sensor to see if an object is detected. Then saved in the val variable.

    if(val < 600) {
        servoAng (180, 6);
        delay    (1000); 

        servoAng (90, 6);
        delay    (1000); 
    }
}

// -----------------------------------------------------------------------------
void setup() {
    Serial.begin (9600);

    servo.attach (servoPin);
    servoAng (90, 2);
}
17

Hi Greg, Roy here again. I live in Hong Kong so that is the reason for my response time being off a little. So far I've tried everything in this list and when I alter the value of angles as suggested above the servo does not rotate. I've copied and pasted your code but plenty of it is a little beyond my level of experience. some of it I have no idea of the syntax. But when I run the Arduino sketch to verify I get the error message as below:

/private/var/folders/zk/1_yd0rj946l4sg6xdl7611ww0000gn/T/.arduinoIDE-unsaved20221011-85098-13ig3yj.fcfrj/sketch_nov11a/sketch_nov11a.ino:39:11: error: two or more data types in declaration of 'loop'
/private/var/folders/zk/1_yd0rj946l4sg6xdl7611ww0000gn/T/.arduinoIDE-unsaved20221011-85098-13ig3yj.fcfrj/sketch_nov11a/sketch_nov11a.ino:50:1: error: expected declaration before '}' token

exit status 1

Compilation error: two or more data types in declaration of 'loop'

18

Hi John... Roy here. When I alter the (angle) code as suggested here the servo does not rotate at all.

19

please post the code with these errors

20

I have copied your sketch code and got this error message when verifying:

/private/var/folders/zk/1_yd0rj946l4sg6xdl7611ww0000gn/T/.arduinoIDE-unsaved20221011-85098-13ig3yj.fcfrj/sketch_nov11a/sketch_nov11a.ino:40:11: error: two or more data types in declaration of 'loop'
/private/var/folders/zk/1_yd0rj946l4sg6xdl7611ww0000gn/T/.arduinoIDE-unsaved20221011-85098-13ig3yj.fcfrj/sketch_nov11a/sketch_nov11a.ino:51:1: error: expected declaration before '}' token

exit status 1

Compilation error: two or more data types in declaration of 'loop'