The same plotting problem, it is appear that one of the marker does not show on the graph but it should have been properly plot and the legend has shown properly too

% Plot
figure;
plot(l_new, angular_a_n, 'b');

Unrecognized function or variable 'l_new'.

xlabel('Arm Length (m)');
ylabel('Angular Acceleration (rad/s^2)');
title('Angular Acceleration vs Arm Length');
grid on;
hold on;
%c
% Find the maximum angular acceleration
[max_a, i_max] = max(angular_a_n);
max_l = length(i_max);
fprintf('Maximum Achievable Angular Acceleration:%.2f rad/s^2 \n',max_a);
%d
plot(l_c, angular_a_c, 'or', 'MarkerFaceColor', 'r');
plot(max_l, max_a, 'og', 'MarkerFaceColor', 'g');
text1=sprintf('Current: %.2f rad/s^2 at length: %.2f m\n', angular_a_c, l_c);
text2=sprintf('Max: %.2f rad/s^2 at length: %.2f m', max_a, max_l);
legend({'Angular Acceleration',text1,text2});

[Elisa]

also my graph does not start at 0

[Elisa]

this is the code for the line

l_new=0.15:0.01:2;
num_l=length(l_new);
angular_a_n= [];
for i = 1:num_l
    l = l_new(i);
    %New Differential Thrust
    delta_T_n = 0.25 * l^0.9;
    
    % Torque
    tor_n = delta_T_n * l;
    
    % New Arm
    v_arm_n = pi * (diam_arm / 2)^2 * l;
    m_arm_n = d_arm * v_arm_n;
    I_arma_n = (1/12) * m_arm_n * l^2;
    
    % New Hub 
    I_hub_n = (1/12) * m_hub * (side_hub^2 + side_hub^2);
    
    % New Motors 
    I_motor_n = 4 * m_motor * l^2;
    
    % New Electronics 
    I_elec_n = 4 * m_elec * (l / 2)^2;
    
    % New Total Moment of Inertia
    I_total_n = I_hub_n + I_arma_n + I_motor_n + I_elec_n;
    %New angular acceleration
    angular_a_n = [angular_a_n, tor_n / I_total_n];
end

Unrecognized function or variable 'diam_arm'.

%b
% Plot
figure;
plot(l_new, angular_a_n, 'b');
xlabel('Arm Length (m)');
ylabel('Angular Acceleration (rad/s^2)');
title('Angular Acceleration vs Arm Length');
grid on;
hold on;

Answer 1

[Walter Roberson]

The green marker is probably covered up by the legend.

[max_a, i_max] = max(angular_a_n);

angular_a_n is a vector. max of it is a scalar. The second output of max() is the location of the maximum, so it will be a scalar.

max_l = length(i_max);

The length of a scalar is 1.

plot(max_l, max_a, 'og', 'MarkerFaceColor', 'g');

max_l is 1. Your are plotting (1, max_a) . max_a is roughly 0.324 . The location (1, 0.324) happens to be under the legend box.

Answer 2

[Jatin]

Hi @Elisa,

After running your code with dummy values I found that your plot does show the marker. You may want to check your logic where you are trying to calcuate the value of "max_l".

max_l = length(i_max);

This will always give the max_l as 1 becuase the length of a scalar is always 1. You may want to update your logic with the following:

max_l = l_new(i_max);

This logic correctly calculates the value of arm length at maximum speed.

Here is the code with dummy values.

l_new=0.15:0.01:2;
diam_arm = 0.05;
d_arm = 0.5;
m_hub = 0.2;
side_hub = 0.1;
m_motor = 0.3;
m_elec = 0.1; 
num_l=length(l_new);
angular_a_n= [];
for i = 1:num_l
    l = l_new(i);
    %New Differential Thrust
    delta_T_n = 0.25 * l^0.9;
    
    % Torque
    tor_n = delta_T_n * l;
    
    % New Arm
    v_arm_n = pi * (diam_arm / 2)^2 * l;
    m_arm_n = d_arm * v_arm_n;
    I_arma_n = (1/12) * m_arm_n * l^2;
    
    % New Hub 
    I_hub_n = (1/12) * m_hub * (side_hub^2 + side_hub^2);
    
    % New Motors 
    I_motor_n = 4 * m_motor * l^2;
    
    % New Electronics 
    I_elec_n = 4 * m_elec * (l / 2)^2;
    
    % New Total Moment of Inertia
    I_total_n = I_hub_n + I_arma_n + I_motor_n + I_elec_n;
    %New angular acceleration
    angular_a_n = [angular_a_n, tor_n / I_total_n]; %#ok<AGROW>
end
l_c = 0.5; % Example current arm length
angular_a_c = 10; % Example current angular acceleration

%b
% Plot
figure;
plot(l_new, angular_a_n, 'b');
xlabel('Arm Length (m)');
ylabel('Angular Acceleration (rad/s^2)');
title('Angular Acceleration vs Arm Length');
grid on;
hold on;

%c
% Find the maximum angular acceleration
[max_a, i_max] = max(angular_a_n)

max_a = 0.2299

i_max = 1

max_l = l_new(i_max)

max_l = 0.1500

fprintf('Maximum Achievable Angular Acceleration:%.2f rad/s^2 \n',max_a);

Maximum Achievable Angular Acceleration:0.23 rad/s^2 

%d
plot(l_c, angular_a_c, 'or', 'MarkerFaceColor', 'r');
plot(max_l, max_a, 'og', 'MarkerFaceColor', 'g');

text1=sprintf('Current: %.2f rad/s^2 at length: %.2f m\n', angular_a_c, l_c);
text2=sprintf('Max: %.2f rad/s^2 at length: %.2f m', max_a, max_l);
legend({'Angular Acceleration',text1,text2});

Hope this helps!

[Elisa]

it helps a lot thank you very much

Answer 3

[Sam Chak]

Hi @Elisa

The idea is to reposition the legend box to a region that it doesn't block the green dot.

max_l   = 1.00;
max_a   = 0.32;
plot(max_l, max_a, 'og', 'MarkerFaceColor', 'g'), grid on
axis([0, 2, 0.26, 0.33])
text2   = sprintf('Max: %.2f rad/s^2 at length: %.2f m', max_a, max_l);
legend({text2}, 'location', 'southwest');