SLIP_Flight.m

function dy = SLIP_Flight(t, q, s)
% SLIP_Flight attempt at a passive SLIP model by Roy X.
% Find (x, y) of the point mass!
% This is the FLIGHT phase DYNAMICS
% s stands for the struct of all the parameters
%
% q = [ x, x dot, y, y dot, ft pos, phase, touchdown theta]
% NOTE: changed the y state vector name to q just for clarity
% Thus, in order to define x and y you must do
% x = y(:,1), y = y(:,3)

% These are the equations of motion for the dynamics of flight phase

    dy(1, 1) = q(2);     % x dot
    dy(2, 1) = 0;        % x double dot
    dy(3, 1) = q(4);     % y dot
    dy(4, 1) = -s.g;     % y double dot
    dy(5, 1) = 0;        % foot position upon touchdown
    dy(6, 1) = 0;        % what phase you're in, but you don't want to set the value here or else it will be part of the integration
    dy(7, 1) = 0;        % touchdown theta
end