torque / force problem

Project for our class. Garage door opening with a electric motor, input for time when child holds on and lets go, also childs weight, plot torque and force with respect to time. I am getting a vertical line in one plot ( barely) and nothing in the other.

I am given a garage door system with equations for force and Torque. The given equations are given in my code. The problem wants me to graph the data, for time going from 0 to 60, and at some time a child with a certain weight jumps on and off, These are inputed in the code, I am having a problem with my graph I feel the code is correct but I am not certain. I have been stariing at it for awhile, Here it is:

function [  ] =Part_B(  )
% This function calculates the force that is created  from a
% underground garage door opening, then from the force calculation it
% calculates the torque on a motor that is attached to the garage door. 
% Both calculations occur between a time period of 0 to 60 seconds.
% During this time period we will also calculate the added force that is
% created when a child hangs onto the door until he lets go
% The output for this data will be represented in a graph
% we are given:
Ld= 16; % this is the length of the door in feet
Wd= 225; % this is the weight of the door in lbs
Ll= 7; % this is the length of the lever arm from motor to door in feet
% we will asssume that the lever arm has negligible weight

% we need to define our inputs and set parameters for them that will be
% within the domain of this system
A= input(' Please enter the weight of the child \n');
% The weight of the child is represented by Wk in the equation
if A<0
    error(' The weight of the child must be a positive integer')
end
B= input('What is the time that the child starts to hold onto the door? \n');
if B < 0 || B > 60
    error('Please enter a time that is between 0 to 60 seconds')
end
C=input('What time does the child let go of the door? \n');
if  C < 0 || C > 60
     error('Please enter a time that is between 0 to 60 seconds')
end
if C < B
    error('The value needs to be greater than the starting time for child')
end

% For efficiency we need to initialize the values for Force, Torque, and
% time; creating arrays for these will help in plotting and calculation
F = zeros([1,60]); % variable assigned for Force
t= zeros ([1,60]); % variable assigned for time 
T= zeros([1,60]); % variable assigned for Torque

% with everything defined we begin the for loop to proceed with the
% calculation
for t=1:60
    O = (3*t); % This value is for the angle we are told that the 
    % for every second the angle increases by 3 degrees, we need this to be
    % in Radians in order to make the correct calculations.
    if t< B && t > C % this calculates the force when the child is not holding on
    F(t)= ((Wd*(Ld/2))* (cos((pi/180)* (O/2)))^2)/(Ll*(1+cos((pi/180)*O)))

      else  % this is for when the child is holding onto the door
      F(t)= ((Wd*(Ld/2)+(A*Ld)) * (cos((pi/180) * (O/2)))^2)/(Ll*(1+cos((pi/180)*O)))

        % we now calculate the Torque on the system

      T(t) = F(t) * Ll * sin(pi/180*(90 - O/2))
      end
  end

    % top subplot
  subplot(2,1,1);
  plot(t,F);
  % bottom subplot
  subplot(2,1,2);
  plot(t,T);

end

[Allen McCoin]

I am sorry but apparently my code did not copy into the post correctly, it went in as stanndard text above, again I am sorry, Thank you for your patience.

[Walter Roberson]

I formatted it for you.

Answer 1

[Geoff]

Yep you have a couple of errors.

First, you set your time variable t as an array of zeros. You do this above your loop, which also uses the variable t. That overwrites your array, so the final value of t is the last value of the loop.

I removed this line (because it's not even used in the loop):

t= zeros ([1,60]); % variable assigned for time

And put the following line just after your loop:

t = 1:60;

Secondly, this line doesn't look right:

if t< B && t > C % this calculates the force when the child is not holding on

It should be this:

if t < B || t > C

Finally, I recommend you put semi-colons at the end of your force and torque calculations to avoid them being constantly displayed during iteration.

-g-