Hi,
I now have finished my self build polargraph and play around with the software. Is it planned to improve the speed by adding a look ahead algorithm? I drive my stepper motors with Pololu drivers and I use accelaration. The problem is that the machine accelerates at each starting point of a line and slows down to the end of each line. Regardless at which angle they are connected. So if you have a lot of lines connected which point in the same direction the machine will always slow down at each connection point.

I modified the source to work with this shield:
http://www.watterott.com/en/Arduino-FabScan-Shield

and I improved the pen up/down methods.

If you want I can send you the code.

Best Regards,
Andreas

Hi sandy,

sorry for the late reply. Here is my code for lifting the pen. It also works if the up position is negative. I added penlift_movePenUpHome for moving the pen up regardless in which position it was before.

Andreas

/**
*  Polargraph Server. - CORE
*  Written by Sandy Noble
*  Released under GNU License version 3.
*  http://www.polargraph.co.uk
*  http://code.google.com/p/polargraph/

Penlift.

This is one of the core files for the polargraph server program.  
This file contains the servo calls that raise or lower the pen from
the page.

*/

void penlift_movePen(int start, int end, int delay_ms)
{
	penHeight.attach(PEN_HEIGHT_SERVO_PIN);
	if(start < end)
	{
  		for (int i=start; i<=end; i++) 
		{
    		penHeight.write(i);
    		delay(delay_ms);
  		}
	}
	else
	{
  		for (int i=start; i>=end; i--) 
		{
    		penHeight.write(i);
    		delay(delay_ms);
  		}
	}
	penHeight.detach();
}

void penlift_movePenUpHome()
{
  penHeight.attach(PEN_HEIGHT_SERVO_PIN);
  penHeight.write(UP_POSITION);
  delay(500);
  penHeight.detach();
  isPenUp = true;
}

void penlift_penUp()
{
  	if (isPenUp == false)
	{
    penlift_movePen(DOWN_POSITION, UP_POSITION, 10);
		isPenUp = true;
	}
}

void penlift_penDown()
{
  	if (isPenUp == true)
	{
	   penlift_movePen(UP_POSITION, DOWN_POSITION, 15);
		 isPenUp = false;
	}
}

void penlift_testServoRange()
{
  penHeight.attach(PEN_HEIGHT_SERVO_PIN);
  for (int i=0; i<200; i++) {
    Serial.println(i);
    penHeight.write(i);
    delay(15);
  }
  penHeight.detach();
}

Andreas I am also really keen to get some look ahead function into the firmware. I think vector drawing would really benefit from a constant feed with less bleeding, increased speed and line smoothness. Also it would allow for large scale painting with an airbrush or similar, and that's what i'm really interested in.

I guess the first thing to do would be have two commands in memory at once. once you know where the machine is headed after the 1st move you can decelerate each of the motors to the speeds required at the start of the 2nd move. Then you need to read the 3rd command asap while moving to point 2. Might run into issues here if the moves can't be read in time while the controller is moving

Also because the motors aren't moving at constant velocities while drawing a straight line there will probably be implications to positioning during the deceleration - ie the motors would need to maintain their velocity ratio while decelerating to the speeds needed at the start of the next move... Pretty confusing but I think this is worth the effort to get rid of the stop start motion. What do you think Sandy?