Can you help and show if any where ive gone wrong with any codes

This code is only for Position Analysis

clc; close all; clear; format compact;
% length of links
r1 = 100;
r2 = 50;
r3 = 780;
r4 = 80;
l4 = 125;
eta = deg2rad(30);
% Angle theta 2
th2 = pi/3:2*pi/36:2*pi+pi/3;
n = length(th2)
% Calculations
L = sqrt(r1^2+r2^2-2*r1*r2.*cos(th2));
Sphi = (r2./L).*sin(th2);
Cphi = (r2^2-r1^2-L.^2)./(-2*r1.*L);
phi = atan2(Sphi, Cphi);
th3 = acos((r4^2-r3^2-L.^2)./(-2*r3.*L))-phi;
Cgamma = (r3^2-r4^2-L.^2)./(-2*r4.*L);
Sgamma = (r3/r4).*sin(th3+phi);
gamma = atan2(Sgamma, Cgamma);
th4 = pi-phi-gamma;
% Use this to find the 3rd join on link 4
all = th4-eta;

% Position of joints
xO2 = 0;
yO2 = 0;
xA = r2*cos(th2);
yA = r2*sin(th2);
xB = xA+r3*cos(th3);
yB = yA+r3*sin(th3);
xO4 = r1;
yO4 = 0;
xC5 = xO4+l4*cos(all);
yC5 = yO4+l4*sin(all);

% These are used to plot the length of each link in the Draw-Linkage
Xcrank = [xO2, xA(1)];
Ycrank = [yO2, yA(1)];
Xcoupler = [xA(1), xB(1)];
Ycoupler = [yA(1), yB(1)];
Xrocker = [xB(1), xO4];
Yrocker = [yB(1), yO4];
Xground = [-1.2*r2, r1+10];
Yground = [yO2, yO4];
XC4C5 = [xO4, xC5(1)];
YC4C5 = [yO4, yC5(1)];
XBC5 = [xB(1), xC5(1)];
YBC5 = [yB(1), yC5(1)];

Draw_linkage = plot(xA, yA, '--r',...
    Xcrank, Ycrank, 'r', Xcoupler, Ycoupler, 'b',...
    Xrocker, Yrocker, 'g', XC4C5, YC4C5, 'g',...
    XBC5, YBC5, 'g', Xground, Yground, '--k', 'linewidth', 1.2);
axis([-r2-r3 2*r2+r3 -2*r2 r4]);
axis equal

for i=1:n
    delete(Draw_linkage);
    
    Xcrank = [xO2, xA(i)];
    Ycrank = [yO2, yA(i)];
    Xcoupler = [xA(i), xB(i)];
    Ycoupler = [yA(i), yB(i)];
    Xrocker = [xB(i), xO4];
    Yrocker = [yB(i), yO4];
    Xground = [-1.2*r2, r1+10];
    Yground = [yO2, yO4];
    XC4C5 = [xO4, xC5(i)];
    YC4C5 = [yO4, yC5(i)];
    XBC5 = [xB(i), xC5(i)];
    YBC4 = [yB(i), yC5(i)];
    
    Draw_linkage = plot(xA, yA, '--r',...
        Xcrank, Ycrank, 'r', Xcoupler, Ycoupler, 'b',...
        Xrocker, Yrocker, 'g', XC4C5, YC4C5, 'g',...
        XBC5, YBC5, 'g', Xground, Yground, '--k', 'linewidth', 1.2);
    axis([-r2-r3 2*r2+r3 -2*r2 r4]);
    axis equal
    F(i) = getframe;
    pause(1/20);
end

movie(F, 2);

Answer 1

[Tanmay Das]

Hi,

atan2(Y,X) returns the four-quadrant inverse tangent (tan-1) of Y and X, which must be real. In the given code, Sgamma is a vector of complex quantities. So it generates an error that "Inputs must be real".

[Daniel Martelli]

Im not really undestanding what you are trying to say

[Tanmay Das]

In your code, you have written these lines:

Sgamma = (r3/r4).*sin(th3+phi);
gamma = atan2(Sgamma, Cgamma);

where Sgamma comes out to be a complex quantity. (You may try printing the value of Sgamma in command window)

However, 'atan2' function only takes real input arguments. So, it gnerated the error that "Inputs must be real"