Design: The design for our CNC mill will consist of three parts: platform, electronics, and software. (The hardware design is based on the work of Tom McWire.)
Platform: The platform consists of two horizontal layers - one which moves in the x-direction and the other in the y-direction - and a motor mounted on an arm capable of moving vertically in the z-direction. Each layer moves on rails and is pulled by a stepper motor. From left to right, the base with arm, x-direction platform, y-direction platform, and z-direction platform with motor.
Electronics: The motor is an old food blender. The platforms will be moved using bi-polar stepper motors with threaded rods attached to their shafts. A L298N Dual H-Bridge will be used to power the motors with the Arduino board providing control. (The motor control circuit is based on the work of Lewis Loflin.)
Program: A complete CNC program will not be produced for the project. A simple CNC program will be written in Excel which will then convert the code into x, y, and z coordinates. The Arduino can read input through a serial port and then output the required motor controls. Stepper motors are controlled by alternating the polarity of the motor's windings. Using the circuit diagram above, the bi-polar step motor can be controlled in three ways by changing the polarity. If the polarity is changed in sequence going down, the motor turns one direction, and if the polarity is changed in sequence going up, the motor turns in the opposite direction. (More can be read about step motors at Stepperworld.)
Wave Drive, One-Phase
(consumes the least power)
Black
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Yellow
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Brown
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Orange
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-
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-
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-
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+
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-
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-
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+
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-
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-
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+
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-
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-
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+
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-
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-
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-
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Hi-Torque, Two-Phase
(improved speed and torque)
Black
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Yellow
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Brown
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Orange
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-
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-
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+
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+
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-
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+
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+
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-
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+
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+
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-
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-
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+
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-
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-
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+
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Half-Step
(doubles stepping resolution)
Black
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Yellow
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Brown
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Orange
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-
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-
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-
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+
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-
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-
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+
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+
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-
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-
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+
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-
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-
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+
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+
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-
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-
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+
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-
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-
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+
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+
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-
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-
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+
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-
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+
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+
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Here is the code to be used for the Arduino:
#ifndef Motor_h
#define Motor_h
#include "Arduino.h"
class Motor
{
public:
Motor(int en, int coil_1, int coil_2);
float drive(float
inches);
private:
int _en;
int _coil_1;
int _coil_2;
int STEPS; //steps per inch
int DELAY_TIME; //delay
time per step
int sequence; //step motor is at this step in sequence of polarity
};
#endif
#include "Arduino.h"
#include "Motor.h"
Motor::Motor(int
en, int coil_1, int
coil_2)
{
pinMode(en, OUTPUT);
pinMode(coil_1, OUTPUT);
pinMode(coil_2, OUTPUT);
_en =
en;
_coil_1
= coil_1;
_coil_2
= coil_2;
STEPS =
4000; //steps per inch
DELAY_TIME = 10; //delay time per step
sequence
= 0;
}
float Motor::drive(float inches)
{
int POLARITY[2][4] = {1, 1, 1, 0, 0, 0, 0, 1};
//motor makes discrete moves, this is the remainder it
didn't turn
float remainder;
//negative inches to move backward
int i = 1; //increment
polarity sequence
if (inches < 0) i = -1; //move
backward through sequence if negative
int turnCounter = abs(inches * STEPS); //total number of steps needed
remainder = inches - turnCounter * STEPS;
digitalWrite(_en, HIGH); //turn output to
stepper on
while (1){
digitalWrite(_coil_1, POLARITY[sequence][1]);
digitalWrite(_coil_2, POLARITY[sequence][2]);
delay(DELAY_TIME);
turnCounter--; //turn completed
//polarity pattern moves to next pattern in sequence
sequence = (sequence + i) % 4;
if (turnCounter == 0) break;
//if finished turning, stop loop
}
digitalWrite(_en, LOW); //turn output to
stepper off
return remainder;
}
/*
This code uses a L298N dual H-bridge
to operate three 4-wire,
1.8 degree/step, bi-polar stepper
motors in high torque,
two-phase mode. Each motor is
attached to a 20 thread/inch rod.
Therefore, it takes 4000 steps for
the nut on the rod
to progress 1 inch.
The circuit diagram at
csmengineeringclub.blogspot.com
shows the pin connections for the
L298N. Pins 5 and 7
control coil 1 and are linked
together with an inverter
on pin 7. Pins 10 and 12 control
coil 2 and are linked
together with an inverter on pin 12.
L298N Pins Function
5, 7 Coil 1
10, 12 Coil 2
6, 11 Enable High (EN)
Arduino digital pins control the
stepper motors.
Ardunio Digital Pins
13 - ENa
12 - Coil 1a
11 - Coil 2a
10 - ENb
9 - Coil 1b
8 - Coil 2b
7 - ENc
6 - Coil 1c
5 - Coil 2c
Arduino analog in-pins control the
calibration buttons.
Arduino Analog In-Pins
0 - x+
1 - x-
2 - y+
3 - y-
4 - z+
5 - z-
The program reads a comma
deliminated text file of x, y, and z
coordinates entered through the
serial port. The origin is at the
bottom left corner of the platform.
*/
#include <Motor.h>
// create 3 motor objects
Motor myMotorX(13, 12, 11);
Motor myMotorY(10, 9, 8);
Motor myMotorZ(7, 6, 5);
void setup(){
Serial.begin(9600);// initialize the serial
port
for (int i = 5; i
<= 13; i++){
pinMode(i, OUTPUT);
}
}//end setup
void loop(){
Serial.println("Is the machine
calibrated? (Y/N)");
int selection;
if (Serial.available() > 0){// user has typed something
selection = Serial.read();
if (selection == 'y'
|| selection == 'Y'){
Serial.println("Enter
coordinates.");
drill();
}
else {
Serial.println("Finished calibrating?
(Y)");
// if buttons are pushed down, move platform in that
direction
while (Serial.available() <= 0){
// keep moving until user has typed something
if (analogRead(A0) > 500) myMotorX.drive(0.001);
if
(analogRead(A1) > 500) myMotorX.drive(-0.001);
if (analogRead(A2) > 500) myMotorY.drive(0.001);
if (analogRead(A3) > 500) myMotorY.drive(-0.001);
if (analogRead(A4) > 500) myMotorZ.drive(0.001);
if (analogRead(A5) > 500) myMotorZ.drive(-0.001);
}// end while
}// end if
}// end if
}//end loop
void drill(){
// drill will be moving between points 1 and 2
float x1, x2;
float y1, y2;
float z1, z2;
// if coordinates available, read it
if (Serial.available() > 0) {
// look for the next valid float in the incoming serial
stream:
x1 =
Serial.parseFloat();
// do it again:
y1 =
Serial.parseFloat();
// do it again:
z1 =
Serial.parseFloat();
}
while (Serial.available() > 0) {
// look for second coordinate
x2 =
Serial.parseFloat();
y2 =
Serial.parseFloat();
z2 =
Serial.parseFloat();
// the smallest distance a platform can move is 1/4000
inch, so to
// calculate the smallest increment the motor should take
to get the
// smoothest linear interpolation, the shortest distance in
each
// direction is calculated and
then multipled by a number less than
// 4000 steps/inch
int n = min (min( abs(x2 - x1), abs(y2 - y1)) ,
abs(z2 - z1) ) * 3000;
for (int i = 0; i
< n; i++){// move platforms
// new coordinate becomes old coordinate so drill can move
to the
// next coordinate
x1 =
x2 - myMotorX.drive( (x2 - x1) / n );
y1 =
y2 - myMotorY.drive( (y2 - y1) / n );
z1 =
z2 - myMotorZ.drive( (z2 - z1) / n );
}
// look for the newline that marks the end of coordinate
data
if (Serial.peek() == '\n')
break;
}//end while
}// end input
#######################################
# Syntax Coloring Map Motor
#######################################
#######################################
# Datatypes (KEYWORD1)
#######################################
Motor KEYWORD1
#######################################
# Methods and Functions (KEYWORD2)
#######################################
# Syntax Coloring Map Motor
#######################################
#######################################
# Datatypes (KEYWORD1)
#######################################
Motor KEYWORD1
#######################################
# Methods and Functions (KEYWORD2)
#######################################
drive KEYWORD2
Base
|
Quantity
|
Unit Price
|
Total
|
Store
|
Plywood 1/2"
|
1
|
$0.00
|
$0.00
|
Own
|
Stud 2" x 4"
|
2
|
$0.00
|
$0.00
|
Own
|
MDF 1/2"
|
1
|
$0.00
|
$0.00
|
Own
|
Aluminum L-Channel
3/4" x 96" x 1/20"
|
1
|
$9.96
|
$9.96
|
Home Depot
|
Aluminum C-Channel
3/4" x 96" x 1/16"
|
1
|
$0.00
|
$0.00
|
Own
|
1", 1-1/2"
Screws
|
$0.00
|
$0.00
|
Own
|
Arm
|
Quantity
|
Unit Price
|
Total
|
Store
|
3/4" Floor Flange
Pipe
|
2
|
$2.19
|
$4.38
|
Home Depot
|
3/4" Elbow Pipe
|
1
|
$2.37
|
$2.37
|
Home Depot
|
3/4" x 6" Pipe
|
1
|
$2.26
|
$2.26
|
Home Depot
|
3/4" x 12" Pipe
|
1
|
$4.45
|
$4.45
|
Home Depot
|
Movement Mechanism
|
Quantity
|
Unit Price
|
Total
|
Store
|
1/4" x 7/8" Ball
Bearing (2x)
|
3
|
$2.37
|
$7.11
|
Home Depot
|
Extension Springs,
1/4" x 1”
|
3
|
$0.00
|
$0.00
|
Own
|
1-1/2" Slotted Truss,
Angle Bracket
|
2
|
$0.00
|
$0.00
|
Own
|
1” x 1” Angle Bracket
|
4
|
$0.00
|
$0.00
|
Own
|
1/4" Hex Nut
|
15
|
$0.06
|
$0.90
|
Home Depot
|
Washers
|
$0.00
|
$0.00
|
Own
|
|
Binder Clips
|
3
|
$0.00
|
$0.00
|
Own
|
1/4"-20 x 7/8"
Coupling Nut (3x)
|
1
|
$1.24
|
$1.24
|
Home Depot
|
1/4"-20 x 36"
Threaded Rod
|
2
|
$1.97
|
$3.94
|
Home Depot
|
Electrical Tape
|
$0.00
|
$0.00
|
Own
|
Drill
|
Quantity
|
Unit Price
|
Total
|
Store
|
Motor
|
1
|
$0.00
|
$0.00
|
Own
|
Dremel 1/8 in.
Multipurpose Cutting Bit
|
1
|
$5.20
|
$5.20
|
Home Depot
|
3/4" x 10' Metal
Hanger Strap
|
1
|
$0.00
|
$0.00
|
Own
|
Metal Epoxy
|
1
|
$0.00
|
$0.00
|
Own
|
Drill Chuck
|
1
|
$0.00
|
$0.00
|
Ow
|
Electronics
|
Quantity
|
Unit Price
|
Total
|
Store
|
Arduino
|
1
|
$0.00
|
$0.00
|
Own
|
Stepper Motor 24V, 1.8
Degree, 1.2A (x3)
|
1
|
$32.99
|
$32.99
|
Ebay
|
Hex Inverter 74LS04N
|
3
|
$0.49
|
$1.47
|
Jameco
|
0.1uF Capacitor
|
10
|
$0.07
|
$0.70
|
Jameco
|
Dual Full Bridge Driver L298N
|
3
|
$2.75
|
$8.25
|
Jameco
|
Schottky Diode 1N5822
|
30
|
$0.16
|
$4.80
|
Jameco
|
AWG26 Wire
|
0
|
$0.00
|
$0.00
|
Own
|
Totals
|
Subtotal
|
Tax, S/H
|
Total
|
|
Home Depot
|
$41.40
|
$3.48
|
$44.88
|
|
Jameco
|
$15.22
|
$1.26
|
$16.48
|
|
Ebay
|
$32.99
|
$6.99
|
$39.98
|
|
Grand Total:
|
$101.34
|
|||
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