Arduino and kop encoder

[SeanPerez]

do i have to divide the rpm by 360 since my encoder has 360 positions in 1 rotation?

[SeanPerez]

i noticed that your code resets back to zero after 60,000 rpm. it is reading much faster that actually spinning. what do i do to make it the actual rpm

My encoder is the kop encoder and it has 360 positions in 1 rotation

[Michael Hill]

Originally Posted by SeanPerez

do i have to divide the rpm by 360 since my encoder has 360 positions in 1 rotation?

Actually, I just modified my code. I realized I had a mistake:

// Controlling a servo position using a potentiometer (variable resistor) 
// by Michal Rinott <http://people.interaction-ivrea.it/m.rinott> 

#include <Servo.h> 
 
Servo motor1;  // create servo object to control a motor 
Servo motor2;  // ditto
 
int potpin = 0;  // analog pin used to connect the potentiometer
int val;    // variable to read the value from the analog pin 
float dt;
volatile byte rpmcount;
float rpm;
unsigned long timeold;

 
void setup() 
{ 
  motor1.attach(9);  // attaches motor 1 on pin 9 to the servo object 
  motor2.attach(10); // ditto
  attachInterrupt(0, rpm_fun, RISING);
  rpmcount = 0;
  rpm = 0;
  timeold = 0;
  digitalWrite(2, HIGH);
  Serial.begin(9600);
} 
 
void loop() 
{ 
  val = analogRead(potpin);            // reads the value of the potentiometer (value between 0 and 1023) 
  val = map(val, 0, 1023, 0, 179);     // scale it to use it with the motor (value between 0 and 180) 
  
  
  if (rpmcount >= 20) {
    dt = (float)(millis() - timeold)/1000;
    Serial.print(dt);
    rpm = rpmcount/dt*60;
    timeold = millis();
    rpmcount = 0;
    Serial.print(" RPM: ");
    Serial.print(rpm);
    Serial.print(" Pot: ");
    Serial.print(val);
    Serial.print("\n");
  }  
  
  motor1.write(val);                  // sets the motor speed according to the scaled value 
  motor2.write(val);
}

void rpm_fun()
{
  rpmcount++;
}

At any rate, when used as an interrupt, it only counts once per revolution.

[SeanPerez]

At any rate, when used as an interrupt, it only counts once per revolution.

it may only count once, but i was getting around 8000 rpm.


with your new code, the faster it spins, the lower the rpm.

[Michael Hill]

Originally Posted by SeanPerez

it may only count once, but i was getting around 8000 rpm.


with your new code, the faster it spins, the lower the rpm.

Are you looking at the first column?

If you are, disregard that. That's the "dt" value. Sorry, I didn't make it very legible. Look at the second set of numbers.

0.43 RPM: 2803.74 Pot: 82

means that 0.43 is the time between calculations, 2803.74 is the revolutions per minute, and 82 is the potentiometer value.

[SeanPerez]

ok now im reading the right number. but it seems the rpm is way to high then the actual rpm.

im spinning it by hand and its reading around 21,000 rpm. this is way to high. im spinning it at around 60 rpm +or- 10 rpm

[Michael Hill]

Originally Posted by SeanPerez

ok now im reading the right number. but it seems the rpm is way to high then the actual rpm.

im spinning it by hand and its reading around 21,000 rpm. this is way to high. im spinning it at around 60 rpm +or- 10 rpm

You didn't multiply it by 360 did you? If not, The arduino board MIGHT somehow me picking up every encoder tick. If that's the case, divide by 360. (Notice that 21000/360 = 58.3)

[Michael Hill]

It would make sense, by the way, if it is. My code is for a hall effect sensor being used as an encoder that reads a screw once per revolution.

[SeanPerez]

sorry if i was unclear but i was looking for code for a encoder that reads 360 positions per revolution compared to your 1 . no worries, all i did was divide your rpm by 360.

[Michael Hill]

Originally Posted by SeanPerez

sorry if i was unclear but i was looking for code for a encoder that reads 360 positions per revolution compared to your 1 . no worries, all i did was divide your rpm by 360.

So you got it working then? Dividing by 360 would be the solution I think.

[Michael Hill]

Oh, and I thought I'd caution you. There's a maximum read rate on the arduinos. It takes about 100 microseconds to take a reading, so it can read about 10,000 times/second. Since you're reading all 360 values every rotation, you've got a maximum of 27.78 rev/sec, or 1666.67 RPM. Not really sure what you're using it for, but keep that in mind.

[docdavies]

Thank you folks. I found this thread very informative and useful.

We are also working to "off-load" more robot functions to an Arduino Mega.

Doc

[SeanPerez]

Originally Posted by Michael Hill

Oh, and I thought I'd caution you. There's a maximum read rate on the arduinos. It takes about 100 microseconds to take a reading, so it can read about 10,000 times/second. Since you're reading all 360 values every rotation, you've got a maximum of 27.78 rev/sec, or 1666.67 RPM. Not really sure what you're using it for, but keep that in mind.

are you sure its 1666? i went up to as high as 2000 multiple times in a row

[SeanPerez]

i think the fastest i could spin it was 2100rpm