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Thread: Pulley Simulation..HELP
 06182008, 04:16 PM #1Member
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Pulley Simulation..HELP
Hi
I am trying to simulate a line being effected by a pulley.
At the moment this is very simple. I have 3 plotted points. 1 The begining point, 2 the pully and 3 the end point. A line is drawn to each point so point 1 to point 2, point 2 to point 3.
I want to say if I move point 1 down then point 2 will stay static but point 3 will move up to point 2 by the equal amount of travel applied to point 1. Can do this easily just on the x axis but when I start mixing in the y axis as well I can't figure out how to plot the new position of point 3. I am guessing I would have to use triganomatry (sp?)
Please help.
 06182008, 04:47 PM #2Member
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It's ok, I have figured it. I just use the x position of the pully and decrease the x position of point 3 whilst doing the same to the y until the x position of 3 is equal to that of the pully. The nearer I get to the pully the more x I decrease. I would like some help later as I will be applying forces and pressures to the pulley system so would like the pulleys to act in different ways. I.e The pulley could be attached to a weight and the top of the pulley connected to a tow point via a elastic chord. So the pulley would move somewhat until the elastic overcomes the weight.
Actually any thoughts and tips would be good
 06182008, 11:51 PM #3Java Code:
import java.awt.*; import java.awt.geom.*; import javax.swing.*; import javax.swing.event.*; public class PulleyTest extends JPanel implements ChangeListener { PulleyModel model = new PulleyModel(200,50,40,400); Rectangle weight = new Rectangle(65, 40); int bitterEndHeight = 100; public void stateChanged(ChangeEvent e) { bitterEndHeight = ((JSlider)e.getSource()).getValue(); repaint(); } protected void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2 = (Graphics2D)g; g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); // draw pulley g2.setPaint(Color.blue); int dia = model.diameter; Point p = model.loc; double x = p.x  dia/2; double y = p.y  dia/2; Ellipse2D.Double pulley = new Ellipse2D.Double(x, y, dia, dia); g2.draw(pulley); // mark center g2.setPaint(Color.orange); g2.fill(new Ellipse2D.Double(p.x2, p.y2, 4, 4)); // int h = getHeight(); int bitterLength = h  bitterEndHeight  p.y; double loadLength = model.getLoadLength(bitterLength); //System.out.printf("bitterLength = %d loadLength = %.1f%n", // bitterLength, loadLength); // check calculations double totalLength = bitterLength + Math.PI*dia/2 + loadLength; //System.out.printf("totalHeight = %.1f%n", totalLength); // locate and draw weight weight.setLocation(p.x+dia/2weight.width/2, (int)(p.y+loadLength)); g2.setPaint(Color.green.darker()); g2.draw(weight); // draw line g2.setPaint(Color.black); x = p.xdia/2; g2.draw(new Line2D.Double(x, p.y, x, p.y+bitterLength)); x = p.x+dia/2; g2.draw(new Line2D.Double(x, p.y, x, p.y+loadLength)); } private JSlider getSlider() { JSlider slider = new JSlider(JSlider.VERTICAL, 10, 280, bitterEndHeight); slider.addChangeListener(this); return slider; } public static void main(String[] args) { PulleyTest test = new PulleyTest(); JFrame f = new JFrame(); f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); f.add(test); f.add(test.getSlider(), "After"); f.setSize(400,400); f.setLocation(200,200); f.setVisible(true); } } class PulleyModel { int diameter; Point loc; int lineLength; PulleyModel(int x, int y, int dia, int line) { loc = new Point(x, y); diameter = dia; lineLength = line; } public double getLoadLength(int bitterLength) { // loadLength = lineLength  bitterLength  circumference/2 return lineLength  bitterLength  Math.PI*diameter/2; } }
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