groundreactionforces.m

```
function [grf,grt,cop] = groundreactionforces(t, x, walk)
% GROUNDREACTIONFORCES Computes ground reaction forces for 2-D rimless
% wheel
% [grf, grt, cop] = groundreactionforces(t, x, walk) computes the ground
% reaction forces in grf, and ground reaction torques in grt, given input
% consisting of time t, state x, and a walk object containing the
% parameters.
% For this model, grf = [fx; fy], the forward horizontal and vertical
% components. grt = tz, the moment about the ground3 axis.
% cop = copx, the center of pressure along the forward horizontal axis.
parms = get(walk, 'parms');
gamma = parms.gamma; rgyr = parms.rgyr;
% q1 = x(1);
% u1 = x(2);
sigma2 = 1/(1 + rgyr*rgyr); % this is sigma-squared from McGeer (1990)
% u1dot = fwalk(t, x, walk); % need state-derivative %ORIGINAL
u_dot = [];
for i = 1:length(x)
u_dot(i,:) = fwalk2(t(i), x(i,:), walk, parms, get(walk, 'bumps')); % %<--------osman
end
% find(u1dot(:,1)-x(:,2) ~=0) %this sould be empty
u1dot= u_dot(:,2);
% acceleration tangential to com path
atang = -u1dot; % minus sign is because path is cw
u1 = x(:,2);
% acceleration normal to path, along leg
anorm = u1.*u1; % this is towards ground
c1 = cos(x(:,1)); s1 = sin(x(:,1));%<--------osman, this was missing
% grf = [c1 s1; s1 -c1]*[atang; anorm]%orginal
grf = [c1.*atang + s1.*anorm s1.*atang-c1.*anorm+1];
grt = 0;
cop = 0;
```