When theta2 makes a complete cycle, I get error message.

clear all
clc

L2 = 10;
L3 = 20;
theta2 = 0:pi/18:2*pi;
% theta2 = pi/12;
omega2 = 1.6;

      theta3 = (2 * pi) + asin((-L2/L3)* sin(theta2))

   L1 = L2 * cos(theta2) + L3 * cos(theta3);

   C = [L2*sin(theta2)*omega2;-L2*cos(theta2)*omega2]
   D = [-L3*sin(theta3) -1 ;L3*cos(theta3) 0]  

    B = inv(D) * C

     plot(theta2,theta3)
   grid on
   xlabel('theta2(degrees)')
  ylabel('theta3(degrees)')
  title('crank angle(theta2) vs link 3 angle(theta3)')

   figure
   plot(theta2,L1)
   grid on
   xlabel('theta2(degrees)')
  ylabel('L1(m)')
  title('crank angle(theta2) vs link 1 angle(L1)')

[Ben Rancici]

What is the real question here? Are you asking for the community to help you debugging your script? If so, why don't you share with us the error message you get?

[KSSV]

Your D is not a square matrix, that's why error popped.

[Ben Rancici]

Indeed, if theta2 is a vector, then D is not square and cannot be inverted.

Answer 1

[KSSV]

clc; clear all ;
clear all
clc
L2 = 10;
L3 = 20;
theta2 = 0:pi/18:2*pi;
% theta2 = pi/12;
omega2 = 1.6;
theta3 = (2 * pi) + asin((-L2/L3)* sin(theta2)) ;
L1 = zeros(1,length(theta3)) ;
for i = 1:length(theta3)
    L1(i) = L2 * cos(theta2(i)) + L3 * cos(theta3(i));
    C = [L2*sin(theta2(i))*omega2;-L2*cos(theta2(i))*omega2] ;
    D = [-L3*sin(theta3(i)) -1 ;L3*cos(theta3(i)) 0] ;
    B = D\C ;
end
plot(theta2,theta3) ;
grid on
xlabel('theta2(degrees)')
ylabel('theta3(degrees)')
title('crank angle(theta2) vs link 3 angle(theta3)')
figure
plot(theta2,L1)
grid on
xlabel('theta2(degrees)')
ylabel('L1(m)')
title('crank angle(theta2) vs link 1 angle(L1)')

[oroskic007]

Thank you so much. Exactly my expectation

Answer 2

[Walter Roberson]

When theta2 has a complete cycle from 0 to 2*Pi, then the sin and cos entries go from [0 1] at the beginning, through a bunch of different possibilities and return to [0 1] at the end. Those lead to the entries in D being the same for the first and last element. Duplicate rows in a matrix to be inverted guarantee that the matrix is singular.

You need to end your theta2 just before it completes a cycle to 2*Pi. For example,

theta2 = 0:pi/18:2*pi;
theta2(end) = [];