Question about Servo function and angle detection at first run.

[i33SoDA]

Greetings,

While waiting for some components for my robotic arm I decided to write the code. Searching for documentation I managed to finish the code but I have a question. Let's see for example the following lines:

int angle1=0;

if(button='1')
{
for(angle1 = 0; angle1 < 180; angle1 += 1)
{
servo_moto1.write(angle1);
delay(5);
}

• as long as button '1' is pressed the servo_motor1 will rotate to one direction 180 degrees.

If I am understanding correctly the motor needs to be physically at 0 degrees for that for-function to work, right?

What happens if physically my motor is at 35 degrees when I first power/run it? Will this for-function break the motor?

Thank you in advance

[system]

It will swing from 35 to 0 in one "go", then start the 1 degree-at-a-time stepping.

A servo on its own should be ok with doing that, but whether or not that breaks anything, will depend on the mechanical setup.

[Slumpert]

Your code snipe is concerning as your seeming to be using a for loop even without a next call, when would it stop as “button” is never checked inside the “for”.

Even the use of a delay 5 makes little sense as it’s a servo motor and it’s going to go to the specified PWM position regardless what the Arduino does next.

[system]

Servos get updated every 20ms and move slowly, so a delay of 5ms is a bit pointless.

[i33SoDA]

It seems that every time when I reset the program, the position of the motor will reset too.

For example if I set the initial angle to 90 degrees, the servo motor first will go at 90 degrees physically and then will start to rotate depending of what I wrote.

It's interesting, I need to find how does the motor know to start at the default position.

[system]

The default position of 90 is in the servo library.

You can specify the position you start the servo at, if 90 doesn't suit, by doing a write() to your preferred position before the attach(). But if it's not already sitting there from the previous time, it will (try to) move to that position.

Unless you use uncommon 4-wire servos like these for example and read the extra wire for position, there is no way of knowing where a servo actually is at any point.

[system]

meltDown:
The default position of 90 [edit: degrees] is in the servo library.

Strictly speaking I should have said the default pulse is 1500 [edit: ms]. From servo.h:

#define DEFAULT_PULSE_WIDTH  1500     // default pulse width when servo is attached

[i33SoDA]

I managed to write this code.

I have a phone witch sends a byte in ASCII code for the bluetooth functin -if-

For example: if bluetooth=='1' , it checks if the ASCII code sent from phone is 49. When any of the arrows/button are stopped being pressed the phone transmits the ASCII code corresponding to X.

I check with a servo motor every button if it works, and it does but strangely when I connect 2 servo motors, in paralel with 5V line and ground + the PWM accordingly to the axis, the motors shake and start moving randomly without pressing any keys.

The following code is:

#include <Servo.h>
int bluetooth=0;
Servo servo_moto1; //functia servo, de fapt e o functie liniara
Servo servo_moto2;
Servo servo_moto3;
Servo servo_moto4;
Servo servo_moto5;
Servo servo_moto6;

int angle1=1;
int angle2=1;
int angle3=1;
int angle4=1;
int angle5=1;
int angle6=1;

void setup()
{
servo_moto1.attach(3); // A1
servo_moto2.attach(4); // A2
servo_moto3.attach(5); // B1
servo_moto4.attach(6); // C1
servo_moto5.attach(7); // D1
servo_moto6.attach(8); // Cleste
Serial.begin(9600); //default comm
}

void loop()
{
if(Serial.available()>0)
{
bluetooth=Serial.read();
}
if(bluetooth=='1') //motorul A1 49,50
{
for(angle1; angle1 < 180; angle1 += 1)
{
servo_moto1.write(angle1);
delay(20);
bluetooth=Serial.read();
if(bluetooth=='X')
{
break;
}
}
}
if(bluetooth=='2')
{
for(angle1; angle1 >= 1; angle1 -= 1)
{
servo_moto1.write(angle1);
delay(20);
bluetooth=Serial.read();
if(bluetooth=='X')
{
break;
}
}
}

if(bluetooth=='3') //motorul A2 51,52
{
for(angle2; angle2 < 180; angle2 += 1)
{
servo_moto2.write(angle2);
delay(20);
bluetooth=Serial.read();
if(bluetooth=='X')
{
break;
}
}
}
if(bluetooth=='4')
{
for(angle2; angle2 >= 1; angle2 -= 1)
{
servo_moto2.write(angle2);
delay(20);
bluetooth=Serial.read();
if(bluetooth=='X')
{
break;
}
}
}

if(bluetooth=='5') //motorul B1 53,54
{
for(angle3; angle3 < 180; angle3 += 1)
{
servo_moto3.write(angle3);
delay(20);
bluetooth=Serial.read();
if(bluetooth=='X')
{
break;
}
}
}
if(bluetooth=='6')
{
for(angle3; angle3 >= 1; angle3 -= 1)
{
servo_moto3.write(angle3);
delay(20);
bluetooth=Serial.read();
if(bluetooth=='X')
{
break;
}
}
}

if(bluetooth=='7') //motorul C1 55,56
{
for(angle4; angle4 < 180; angle4 += 1)
{
servo_moto4.write(angle4);
delay(20);
bluetooth=Serial.read();
if(bluetooth=='X')
{
break;
}
}
}
if(bluetooth=='8')
{
for(angle4; angle4 >= 1; angle4 -= 1)
{
servo_moto4.write(angle4);
delay(20);
bluetooth=Serial.read();
if(bluetooth=='X')
{
break;
}
}
}

if(bluetooth=='9') //motorul D1 55,56
{
for(angle5; angle5 < 180; angle5 += 1)
{
servo_moto5.write(angle5);
delay(20);
bluetooth=Serial.read();
if(bluetooth=='X')
{
break;
}
}
}
if(bluetooth=='0')
{
for(angle5; angle5 >= 1; angle5 -= 1)
{
servo_moto5.write(angle5);
delay(20);
bluetooth=Serial.read();
if(bluetooth=='X')
{
break;
}
}
}

if(bluetooth=='A') //motorul cleste 65,66
{
for(angle6; angle6 < 180; angle6 += 1)
{
servo_moto6.write(angle6);
delay(20);
bluetooth=Serial.read();
if(bluetooth=='X')
{
break;
}
}
}
if(bluetooth=='B')
{
for(angle6; angle6 >= 1; angle6 -= 1)
{
servo_moto6.write(angle6);
delay(20);
bluetooth=Serial.read();
if(bluetooth=='X')
{
break;
}
}
}

}

What I am doing wrong?

[vinceherman]

i33SoDA:
What I am doing wrong?

Failing to use code tags? If you have to ask, go read the sticky post at the top of the forum named How to use this forum - please read.

Please give us a wiring diagram of your project. Pencil, paper and a camera are good enough. Pay special attention to how you power the servos.

Hint, 95% of all servo problems are inadequate power supply.

[slipstick]

If you'd done any reading of the many threads about servos in this forum you'd know that powering even one small servo from the Arduino's 5V pin is a bad idea. More than one is a very bad idea. Trying to power 6 servos from that low current 5V pin is sheer insanity.

It would be quite surprising if you haven't already damaged the Arduino. Power your servos from a separate supply, 4 or 5 NiMH rechargeable cells might probably be o.k., depending on exactly what servos you are using.

Steve

[i33SoDA]

Thank you all for the information.

It works perfectly now and I understand perfectly what I did wrong.

You guys rock!