A Better Turret

ISR Motion Control

Reworked the code to use an ISR (Interrupt Service Routine).

The ISR is pretty heavy duty but with the code optimisation it runs in less than 25 us. So it will run with a 16 MHz input clock (i.e. 31372.55 Hz interrupt rate). Still I slowed input clock down to 2 MHz for a 3921.57 Hz interrupt rate. As there is no ramp code, it is likely the stepper motors will miss steps if you try to go too fast.

Here is the updated code:

/*
  Simple 3 Axis Motion Controller
  ===============================
  Written by Alan Cooper (agp.cooper@gmail.com)
  This work is licensed under the Creative Commons Attribution-NonCommercial 2.5 License.
  This means you are free to copy and share the code (but not to sell it).
*/

// Motor controller (CNC board) pin mapping: 
#define DirX     2
#define DirY     3
#define DirZ     4
#define StepX    5
#define StepY    6
#define StepZ    7
#define Enable   8  // Active low
#define Laser   12  // Turn laser on or off

// Set motion (rate) steps per second
unsigned long rate=1000;

// Motor Controller direction settings
bool xReverse=false;
bool yReverse=true;
bool zReverse=false;

/* Motion ISR */
volatile long xNew=0;           // The target X co-ordinate
volatile long yNew=0;           // The target Y co-ordinate
volatile long zNew=0;           // The target Z co-ordinate
volatile long xCurrent=0;       // The current X co-ordinate
volatile long yCurrent=0;       // The current Y co-ordinate
volatile long zCurrent=0;       // The current Z co-ordinate
volatile long steps=-1;         // Number of steps remaining in motion
volatile unsigned int magic=0;  // Magic number (used by ISR)
volatile unsigned int phase=0;  // Accumulator (used by ISR)
ISR(TIMER2_OVF_vect)
{
  static long stepX,stepY,stepZ;
  static long dx,dy,dz,ax,ay,az,sx,sy,sz,mx,my,mz;
  
  if (phase<0x8000) {
    phase+=magic;
    if (phase>=0x8000) {
      if (steps>0) {
        // Advance steppers
        stepX=0;
        stepY=0;
        stepZ=0;
        if ((ax>=ay)&&(ax>=az)) {
          if (my>=0) {
            my-=ax;
            stepY=sy;
          }
          if (mz>=0) {
            mz-=ax;
            stepZ=sz;
          }
          my+=ay;
          mz+=az;
          stepX=sx;
        } else if ((ay>=ax)&&(ay>=az)) {
          if (mx>=0) {
            mx-=ay;
            stepX=sx;
          }
          if (mz>=0) {
            mz-=ay;
            stepZ=sz;
          }
          mx+=ax;
          mz+=az;
          stepY=sy;
        } else {
          if (mx>=0) {
            mx-=az;
            stepX=sx;
          }
          if (my>=0) {
            my-=az;
            stepY=sy;
          }
          mx+=ax;
          my+=ay;
          stepZ=sz;
        }
        xCurrent+=stepX;
        yCurrent+=stepY;
        zCurrent+=stepZ;
        // Step HIGH
        if (stepX!=0) PORTD|=1<<StepX;
        if (stepY!=0) PORTD|=1<<StepY;
        if (stepZ!=0) PORTD|=1<<StepZ;
        steps--;
        // Disable ISR 
        if (steps==0) steps=-1;
      }
    }
    if (steps==0) {
      // Determine next movement parameters
      dx=xNew-xCurrent;
      dy=yNew-yCurrent;
      dz=zNew-zCurrent;
      // Check that there is something to do
      if ((dx!=0)||(dy!=0)||(dz!=0)) {
        ax=abs(dx);
        ay=abs(dy);
        az=abs(dz);
        sx=xNew<xCurrent?-1:xNew>xCurrent?1:0;
        sy=yNew<yCurrent?-1:yNew>yCurrent?1:0;
        sz=zNew<zCurrent?-1:zNew>zCurrent?1:0;
        if ((ax>=ay)&&(ax>=az)) {
          mx=0;
          my=ay-(ax>>1);
          mz=az-(ax>>1);
          steps=ax;
        } else if ((ay>=ax)&&(ay>=az)) {
          mx=ax-(ay>>1);
          my=0;
          mz=az-(ay>>1);
          steps=ay;
        } else {
          mx=ax-(az>>1);
          my=ay-(az>>1);
          mz=0;
          steps=az;
        }
        // Set the stepper directions
        if (xReverse) {
          // digitalWrite(DirX,(1-sx)>>1);
          if (sx==1) PORTD&=~(1<<DirX); else PORTD|=1<<DirX;
        } else {
          // digitalWrite(DirX,(sx+1)>>1);
          if (sx==-1) PORTD&=~(1<<DirX); else PORTD|=1<<DirX;
        } 
        if (yReverse) {
          // digitalWrite(DirY,(1-sy)>>1);
          if (sy==1) PORTD&=~(1<<DirY); else PORTD|=1<<DirY;
        } else {
          // digitalWrite(DirY,(sy+1)>>1);
          if (sy==-1) PORTD&=~(1<<DirY); else PORTD|=1<<DirY;
        } 
        if (zReverse) {
          // digitalWrite(DirZ,(1-sz)>>1);
          if (sz==1) PORTD&=~(1<<DirZ); else PORTD|=1<<DirZ;
        } else {
          // digitalWrite(DirZ,(sz+1)>>1);
          if (sz==-1) PORTD&=~(1<<DirZ); else PORTD|=1<<DirZ;
        } 
      }
    }
  } else {
    phase+=magic;
    // Reset step LOW
    PORTD&=~(1<<StepX);
    PORTD&=~(1<<StepY);
    PORTD&=~(1<<StepZ);
  }
}

#include <math.h> // For PI, radians(), sin() and cos()
int iSin[360];
int iCos[360];
void setup()
{
  // LED
  pinMode(LED_BUILTIN,OUTPUT);

  // Initialise Motor Controller
  pinMode(DirX,OUTPUT);
  pinMode(StepX,OUTPUT);
  pinMode(DirY,OUTPUT);
  pinMode(StepY,OUTPUT);
  pinMode(DirZ,OUTPUT);
  pinMode(StepZ,OUTPUT);
  pinMode(Enable,OUTPUT);
  pinMode(Laser,OUTPUT);

  digitalWrite(DirX,LOW);
  digitalWrite(StepX,LOW);
  digitalWrite(DirY,LOW);
  digitalWrite(StepY,LOW);
  digitalWrite(DirZ,LOW);
  digitalWrite(StepZ,LOW);
  digitalWrite(Enable,LOW);   // Active low
  digitalWrite(Laser,LOW);    // Active high

  // Disable interrupts
  cli();

  // Use Timer 2 for ISR 
  // Good for ATmega48A/PA/88A/PA/168A/PA/328/P
  TIMSK2=0;                                     // Timer interrupts off
  TCCR2A=(0<<COM2A0)|(0<<COM2B0)|(1<<WGM20);    // Phase correct PWM, no output
  TCCR2B=(0<<WGM22)|(2<<CS20);                  // 2 MHz clock (3921.57 Hz)
  OCR2A=128;                                    // Set 50% duty
  TIMSK2=(1<<TOIE2);                            // Set interrupt on overflow (=BOTTOM)

  // Enable interrupts
  sei();
  
  // Prepare circle array
  for (int i=0;i<360;i++) {
    iSin[i]=(int)(200*sin(radians(i)));
    iCos[i]=(int)(200*cos(radians(i)));   
  }
  
  // Restart Timer
  phase=0;
  magic=rate*52224/3125;   // 2 MHz clock
}

void loop()
{
  // Used to keep track of motion
  static int angle=-1;
  
  // Update only when "steps==-1"
  if (steps==-1) {
    // Make a circle
    if (angle==-1) {
      digitalWrite(Laser,LOW);
      angle=0;
      xNew=iCos[angle];
      yNew=iSin[angle];
      zNew=0;
    } else {
      digitalWrite(Laser,HIGH);
      angle+=15;
      if (angle>=360) angle=0;
      xNew=iCos[angle];
      yNew=iSin[angle];
      zNew=0;
    }
    // Set ready for ISR
    steps=0;
    
    // Working indicator
    digitalWrite(LED_BUILTIN,!digitalRead(LED_BUILTIN));    
  }
}

AlanX

Update to Code

Spent the morning checking the code to determine why the X axis motor controller smoked. I don't know! The code seems to be doing what it should.

The code now scans a circles. The circle is pretty rough:

Set the driver to 1/8 micro-steps:

It has taken me a while to determine that what I am seeing is overshoot:

The overshoot is in the order of half a full step. Unfortunately there is not much I can do about it.

Here is the current code:

/*
  Simple 3 Axis Motion Controller
  ===============================
  Written by Alan Cooper (agp.cooper@gmail.com)
  This work is licensed under the Creative Commons Attribution-NonCommercial 2.5 License.
  This means you are free to copy and share the code (but not to sell it).
*/
#include <math.h> // For PI, radians(), sin() and cos()

// Motor controller (CNC board) pin mapping: 
#define DirX     2
#define DirY     3
#define DirZ     4
#define StepX    5
#define StepY    6
#define StepZ    7
#define Enable   8  // Active low
#define Laser   12  // Turn laser on or off

// Motor Controller direction settings
bool xReverse=false;
bool yReverse=true;
bool zReverse=false;

// Movement control parameters
long stepCountDown;              // Movement steps remaining
unsigned long movementRate;      // Steps per second
unsigned long movementInterval;  // Step period (uS)
unsigned long movementRampIncr;  // Step period (uS)
long xNew,yNew,zNew;             // New co-ordinates
long xCurrent,yCurrent,zCurrent; // Current co-ordinates

void motionControl(void)
{  
  static unsigned long movementPreviousMicros=0;
  static unsigned long movementCurrentMicros=0;
  static unsigned long movementRamp;
  static long stepCountUp=0; 
  static long stepX,stepY,stepZ;
  static long dx,dy,dz,ax,ay,az,sx,sy,sz,mx,my,mz;

  // Process motion command at end of current movement
  if (stepCountDown==-1) {
    stepCountDown=0;
    stepCountUp=0;

    // Determine movement parameters
    dx=xNew-xCurrent;
    dy=yNew-yCurrent;
    dz=zNew-zCurrent;
    ax=abs(dx);
    ay=abs(dy);
    az=abs(dz);
    sx=xNew<xCurrent?-1:xNew>xCurrent?1:0;
    sy=yNew<yCurrent?-1:yNew>yCurrent?1:0;
    sz=zNew<zCurrent?-1:zNew>zCurrent?1:0;
    if ((ax>=ay)&&(ax>=az)) {
      mx=0;
      my=ay-(ax>>1);
      mz=az-(ax>>1);
      stepCountDown=ax;
    } else if ((ay>=ax)&&(ay>=az)) {
      mx=ax-(ay>>1);
      my=0;
      mz=az-(ay>>1);
      stepCountDown=ay;
    } else {
      mx=ax-(az>>1);
      my=ay-(az>>1);
      mz=0;
      stepCountDown=az;
    }

    // Set counters
    if (stepCountDown>0) {
      stepCountUp=1;
    } else {
      stepCountDown=-1;
      stepCountUp=-1;        
    }

    // Set the stepper directions
    if (xReverse) {
      digitalWrite(DirX,(1-sx)>>1);
    } else {
      digitalWrite(DirX,(sx+1)>>1);
    } 
    if (yReverse) {
      digitalWrite(DirY,(1-sy)>>1);
    } else {
      digitalWrite(DirY,(sy+1)>>1);
    }
    if (zReverse) {
      digitalWrite(DirZ,(1-sz)>>1);
    } else {
      digitalWrite(DirZ,(sz+1)>>1);
    }
  }

  // Advance Steppers 
  if (stepCountDown>0) {
    movementRamp=movementInterval;
    if ((stepCountUp==1)||(stepCountDown==1)) movementRamp+=movementRampIncr;
    
    movementCurrentMicros=micros();    
    if (movementCurrentMicros-movementPreviousMicros>movementRamp) {
      movementPreviousMicros=movementCurrentMicros;
            
      // Advance steppers
      stepX=0;
      stepY=0;
      stepZ=0;
      if ((ax>=ay)&&(ax>=az)) {
        if (my>=0) {
          my-=ax;
          stepY=sy;
        }
        if (mz>=0) {
          mz-=ax;
          stepZ=sz;
        }
        my+=ay;
        mz+=az;
        stepX=sx;
      } else if ((ay>=ax)&&(ay>=az)) {
        if (mx>=0) {
          mx-=ay;
          stepX=sx;
        }
        if (mz>=0) {
          mz-=ay;
          stepZ=sz;
        }
        mx+=ax;
        mz+=az;
        stepY=sy;
      } else {
        if (mx>=0) {
          mx-=az;
          stepX=sx;
        }
        if (my>=0) {
          my-=az;
          stepY=sy;
        }
        mx+=ax;
        my+=ay;
        stepZ=sz;
      }
      xCurrent+=stepX;
      yCurrent+=stepY;
      zCurrent+=stepZ;

      // Step pulse (high for at least 10 us)
      digitalWrite(StepX,abs(stepX));
      digitalWrite(StepY,abs(stepY));
      digitalWrite(StepZ,abs(stepZ));
      delayMicroseconds(10);
      digitalWrite(StepX,LOW);
      digitalWrite(StepY,LOW);
      digitalWrite(StepZ,LOW);
      stepCountDown--;
      stepCountUp++;

      // Flag end of movement 
      if (stepCountDown==0) {
        stepCountDown=-1;
        stepCountUp=-1;
      }
      
    }
    
  } else {
    movementPreviousMicros=micros(); // Reset movement rate clock to ensure near full cycle on start
  }
}

int iSin[360];
int iCos[360];

void setup()
{
  // Initialise Motor Controller
  // Note: The motor controller is using 1/16 micro-stepping
  pinMode(DirX,OUTPUT);
  pinMode(StepX,OUTPUT);
  pinMode(DirY,OUTPUT);
  pinMode(StepY,OUTPUT);
  pinMode(DirZ,OUTPUT);
  pinMode(StepZ,OUTPUT);
  pinMode(Enable,OUTPUT);
  pinMode(Laser,OUTPUT);
  digitalWrite(DirX,LOW);
  digitalWrite(StepX,LOW);
  digitalWrite(DirY,LOW);
  digitalWrite(StepY,LOW);
  digitalWrite(DirZ,LOW);
  digitalWrite(StepZ,LOW);
  digitalWrite(Enable,LOW); // Active low
  digitalWrite(Laser,LOW);  // Active high
  
  // Set Global Variables
  xNew=0;
  yNew=0;
  zNew=0;
  xCurrent=0;
  yCurrent=0;
  zCurrent=0;
  stepCountDown=-1;                      // Number of steps remaining in motion
  movementRate=2000;                     // Step per second
  movementInterval=1000000/movementRate; // Micro-seconds
  movementRampIncr=500;                  // Micro-seconds
  // LED
  pinMode(LED_BUILTIN,OUTPUT);
  digitalWrite(LED_BUILTIN,LOW);
  
  // Prepare circle array
  for (int i=0;i<360;i++) {
    iSin[i]=(int)(200*sin(radians(i)));
    iCos[i]=(int)(200*cos(radians(i)));   
  }
}

void loop()
{
  // LED timer
  static unsigned long intervalMillisLED=0;
  static unsigned long currentMillisLED=0;
  static unsigned long previousMillisLED=0;

  // Use LED to indicate working
  if (stepCountDown==0) {
    intervalMillisLED=1000;
  } else {
    intervalMillisLED=100;    
  }
  currentMillisLED=millis();
  if (currentMillisLED-previousMillisLED>intervalMillisLED) {
    previousMillisLED=currentMillisLED;   
    digitalWrite(LED_BUILTIN,!digitalRead(LED_BUILTIN));
  }

  /* Motion Command */
  static int angle=-1;
  // Make a circle
  if (stepCountDown==-1) {
    if (angle==-1) {
      digitalWrite(Laser,LOW);
      angle=0;
      xNew=iCos[angle];
      yNew=iSin[angle];
      zNew=0;
    } else {
      digitalWrite(Laser,HIGH);
      angle+=15;
      if (angle>=360) angle=0;
      xNew=iCos[angle];
      yNew=iSin[angle];
      zNew=0;
    }  
  }

  // Process Motion Command
  motionControl();
}

Well that just about wraps it up.

AlanX

Code

I wrote some code (using Bresenham's algorithm) for the turret:

/*
  Simple 3 Axis Motion Controller
  ===============================
  Written by Alan Cooper (agp.cooper@gmail.com)
  This work is licensed under the Creative Commons Attribution-NonCommercial 2.5 License.
  This means you are free to copy and share the code (but not to sell it).
*/

// Motor controller (CNC board) pin mapping: 
#define DirX     2
#define DirY     3
#define DirZ     4
#define StepX    5
#define StepY    6
#define StepZ    7
#define Enable   8  // Active low
#define Laser   12  // Turn laser on or off

// Motor Controller direction settings
bool xReverse=false;
bool yReverse=true;
bool zReverse=false;

// Movement control parameters
bool pause=false;                // Pause movement
long rampSteps;                  // start and stop ramp steps
long stepCountDown;              // Movement steps remaining
long stepCountUp;                // Movement steps completed
long movementRate;               // Steps per second
long movementInterval;           // Step period (uS)
long ramp;                       // Ramp up/down period
long xNew,yNew,zNew;             // New co-ordinates
long xCurrent,yCurrent,zCurrent; // Current co-ordinates

void motionControl(void)
{  
  static unsigned long movementPreviousMicros=0;
  static unsigned long movementCurrentMicros=0;
  static long stepX,stepY,stepZ;
  static long dx,dy,dz,ax,ay,az,sx,sy,sz,mx,my,mz;

  // Process motion at end of current movement
  if (stepCountDown==-1) {
    stepCountDown=0;
    stepCountUp=0;

    // Determine movement parameters
    dx=xNew-xCurrent;
    dy=yNew-yCurrent;
    dz=zNew-zCurrent;
    ax=abs(dx);
    ay=abs(dy);
    az=abs(dz);
    sx=xNew<xCurrent?-1:xNew>xCurrent?1:0;
    sy=yNew<yCurrent?-1:yNew>yCurrent?1:0;
    sz=zNew<zCurrent?-1:zNew>zCurrent?1:0;
    if ((ax>=ay)&&(ax>=az)) {
      mx=0;
      my=ay-(ax>>1);
      mz=az-(ax>>1);
      stepCountDown=ax;
    } else if ((ay>=ax)&&(ay>=az)) {
      mx=ax-(ay>>1);
      my=0;
      mz=az-(ay>>1);
      stepCountDown=ay;
    } else {
      mx=ax-(az>>1);
      my=ay-(az>>1);
      mz=0;
      stepCountDown=az;
    }

    // Set counters
    if (stepCountDown>0) {
      stepCountUp=1;
    } else {
      stepCountDown=-1;
      stepCountUp=-1;        
    }

    // Set the stepper directions
    if (xReverse) {
      digitalWrite(DirX,(1-sx)>>1);
    } else {
      digitalWrite(DirX,(sx+1)>>1);
    } 
    if (yReverse) {
      digitalWrite(DirY,(1-sy)>>1);
    } else {
      digitalWrite(DirY,(sy+1)>>1);
    }
    if (zReverse) {
      digitalWrite(DirZ,(1-sz)>>1);
    } else {
      digitalWrite(DirZ,(sz+1)>>1);
    }

  }

  // Advance Steppers 
  if ((pause==false)&&(stepCountDown>0)) {
    movementCurrentMicros=micros();
    if (movementCurrentMicros-movementPreviousMicros>ramp) {
      movementPreviousMicros=movementCurrentMicros;
      
      // Start/stop ramp
      if (stepCountUp<=rampSteps) ramp-=movementInterval;
      if (stepCountDown<=rampSteps) ramp+=movementInterval;
      
      // Advance steppers
      stepX=0;
      stepY=0;
      stepZ=0;
      if ((ax>=ay)&&(ax>=az)) {
        if (my>=0) {
          my-=ax;
          stepY=sy;
        }
        if (mz>=0) {
          mz-=ax;
          stepZ=sz;
        }
        my+=ay;
        mz+=az;
        stepX=sx;
      } else if ((ay>=ax)&&(ay>=az)) {
        if (mx>=0) {
          mx-=ay;
          stepX=sx;
        }
        if (mz>=0) {
          mz-=ay;
          stepZ=sz;
        }
        mx+=ax;
        mz+=az;
        stepY=sy;
      } else {
        if (mx>=0) {
          mx-=az;
          stepX=sx;
        }
        if (my>=0) {
          my-=az;
          stepY=sy;
        }
        mx+=ax;
        my+=ay;
        stepZ=sz;
      }
      xCurrent+=stepX;
      yCurrent+=stepY;
      zCurrent+=stepZ;

      // Step pulse (high for at least 10 us)
      digitalWrite(StepX,abs(stepX));
      digitalWrite(StepY,abs(stepY));
      digitalWrite(StepZ,abs(stepZ));
      delayMicroseconds(10);
      digitalWrite(StepX,LOW);
      digitalWrite(StepY,LOW);
      digitalWrite(StepZ,LOW);
      stepCountDown--;
      stepCountUp++;

      // Flag end of movement 
      if (stepCountDown==0) {
        stepCountDown=-1;
        stepCountUp=-1;
      }
      
    }
    
  } else {
    movementPreviousMicros=micros(); // Reset movement rate clock to ensure near full cycle on start
  }
  
}

void setup()
{
  // Initialise Motor Controller
  // Note: The motor controller is using 1/16 micro-stepping
  pinMode(DirX,OUTPUT);
  pinMode(StepX,OUTPUT);
  pinMode(DirY,OUTPUT);
  pinMode(StepY,OUTPUT);
  pinMode(DirZ,OUTPUT);
  pinMode(StepZ,OUTPUT);
  pinMode(Enable,OUTPUT);
  pinMode(Laser,OUTPUT);
  digitalWrite(DirX,LOW);
  digitalWrite(StepX,LOW);
  digitalWrite(DirY,LOW);
  digitalWrite(StepY,LOW);
  digitalWrite(DirZ,LOW);
  digitalWrite(StepZ,LOW);
  digitalWrite(Enable,LOW); // Active low
  digitalWrite(Laser,LOW);  // Laser off
  
  // Reset Global Variables
  pause=false;
  xNew=0;
  yNew=0;
  zNew=0;
  xCurrent=0;
  yCurrent=0;
  zCurrent=0;
  stepCountDown=-1;
  stepCountUp=-1;
  movementRate=3200;                     // Step per second
  movementInterval=1000000/movementRate; // Micro-seconds
  rampSteps=6;                           // Number for steps for ramp up/down
  
  // Precalculate ramp constant
  ramp=movementInterval*(rampSteps+1);
  
  // LED
  pinMode(LED_BUILTIN,OUTPUT);
  digitalWrite(LED_BUILTIN,LOW);
}

void loop()
{
  // Used to keep track of motion
  static int state=0;

  // LED timer
  static unsigned long intervalMillisLED=0;
  static unsigned long currentMillisLED=0;
  static unsigned long previousMillisLED=0;

  // Use LED to indicate working
  if (stepCountDown==0) {
    intervalMillisLED=1000;
  } else {
    intervalMillisLED=100;    
  }
  currentMillisLED=millis();
  if (currentMillisLED-previousMillisLED>intervalMillisLED) {
    previousMillisLED=currentMillisLED;   
    digitalWrite(LED_BUILTIN,!digitalRead(LED_BUILTIN));
  }

  /* Motion Command */
  // Line scanner (-100 to 100 x -100 to 100 )
  if (stepCountDown==-1) {
    if ((state&2)==0) {
      // Laser off
      digitalWrite(Laser,LOW);
      xNew=-100;
      yNew=-100+(state>>1);
      zNew=0;
    } else {
      // Laser on
      digitalWrite(Laser,HIGH);
      xNew=+100;
      yNew=-100+(state>>1);
      zNew=0;
    }
    state++;
    if (state>401) state=0;
  }

  /* Process Motion Command */
  motionControl();

}

The code scans left to right, top to bottom, 201 lines high by 201 pixels wide.

I set the stepper drive up for 0.5A per phase (because the 12v wall plug power supply is a bit under rated for this application) and 1/16 micro stepping.

The CNC board has a design fault in that the micro-steeping shunts are to ground rather than to Vcc, so it is alway set to full step regardless of the shunt setting. I had to jump the shunts pins to Vcc.

The code still needs fine tuning to peak the maximum step rate. It is currently running fine at 3200 PPS (60 RPM).

Assembled and Operating

Here is the turret assembled and operating:

And here is part of the trace on the wall about 5m away:

It is only about 50% of the trace due to the camera shutter speed.

Notice the wiggle! It is about a one micro step (i.e. 1/16 of a full step) high and is quite consistent, probably vibration. If you watch each scan line, some scan lines appear to not move at 1/16 micro stepping. Suggesting the turret accuracy is about 1/8 of a step or about 0.1 degrees. For the next iteration I will drop back to 1/8 micro stepping.

Magic

Inspirational

I found this doing an Internet search of "Animatronics":

Source: "See RoboBones and RoboHead" (http://www.animatronics.org)

Back to Work

Elected not to shunt the external Nano power supply to the motor power supply.

The external power supply input has a schottky to protected against reverse power supply connections. This has the unintended consequence of preventing back EMF from returning to the battery (usually desirable). Instead any back EMF has to be absorbed by the driver boards or the Nano board.

I had lots of problems with back EMF trying to use a common external battery in the past so this time around I will have two separate power supplies.

Added some cable sleeves:

Working on the Code

A bit more complicated then I expected. Do I want to move at an arbitary  direction? I suppose I do, so I will gave to code a Bessenham's line drawing algorithm.

Set up an Interrupt Service Routine (ISR) for the step pulse generator. I have limited the maximum pulse rate to 500 PPS, which is safe from a standing start for full step operation for nearly all common stepper motors. Should be able to bump this up for micro-stepping.

Magic