Need help with car suspension dampening, current code is exp growing.

Currently trying to model a cars suspension as it runs over a bump, however, my current code is actually growing intstead of dampening. Below are the assignment details as well, my current code:

clear

Mc = 401; %Weight

Mw = 48; %Wheel Mass

Ds = 2300; % Susp Damping Coef

Cs = 230000; % Susp Spring Coef

Cw = 250000; %Wheel Spring Coef

Wact = 0.001; % WActuator Time Const

t = 0; %intial Time

dt = 0.001;

Zc = 0; % Displacement Chass

Zw = 0; % Displacement Wheel

Zr = 0; %Disp Road

Vw = 0; %intial speed wheel vertical

Vc = 0; %intial speed Chassis Vertical

U=0;

alp = 0;

bet = 0;

u = U*exp(-alp*(t(end)-t(1)))*cos(2*pi*bet*(t(end)-t(1)));

Fs = 0; %leaving as 0 until we figure out the non-damp force graphing

Fs(end+1) = Fs(end) + ((Fs(end)/Wact)+(1/Wact)*u)*dt; %Damp force

Aw = 0; %intial Wheel Acc

Ac = 0; %intial Chassis Acc

while t(end) < 5

if t(end) > 1 && t(end) < 1.11

Zr = -0.5;

Aw(end+1) = -(1/Mw)*((Cw+Cs)*Zw(end) + Cs*Zc(end) + Ds*(Vc(end) - Vw(end)) + Cw*Zr(end)-Fs(end));

Vw(end+1) = Vw(end) + Aw(end)*dt;

Zw(end+1) = Zw(end) + Vw(end)*dt;

Ac(end+1) = (1/Mc)*(Cs*(Zw(end)-Zc(end))+Ds*(Vw(end)-Vc(end))+Fs(end));

Vc(end+1) = Vc(end) + Ac(end)*dt;

Zc(end+1) = Zc(end) + Vc(end)*dt;

t(end+1) = t(end) + dt;

else

Zr = 0;

Aw(end+1) = -(1/Mw)*((Cw+Cs)*Zw(end) + Cs*Zc(end) + Ds*(Vc(end) - Vw(end)) + Cw*Zr(end)-Fs(end));

Vw(end+1) = Vw(end) + Aw(end)*dt;

Zw(end+1) = Zw(end) + Vw(end)*dt;

Ac(end+1) = (1/Mc)*(Cs*(Zw(end)-Zc(end))+Ds*(Vw(end)-Vc(end))+Fs(end));

Vc(end+1) = Vc(end) + Ac(end)*dt;

Zc(end+1) = Zc(end) + Vc(end)*dt;

t(end+1) = t(end) + dt;

end

end

plot(t,Zc)

% position, velocity, acceleration of the wheel/chass

Answer 1

[Chris]

Looking at the image, a_w and a_c are independent of previous acceleration values.

Aw(end+1) = -(1/Mw)*((Cw+Cs)*Zw(end) + Cs*Zc(end) + Ds*(Vc(end) - Vw(end)) + Cw*Zr(end)-Fs(end));
Ac(end+1) = (1/Mc)*(Cs*(Zw(end)-Zc(end))+Ds*(Vw(end)-Vc(end))+Fs(end));

You also have pulled a minus sign to the front, when it should only apply to the first term.

Aw(end+1) = (1/Mw)*(-(Cw+Cs)*Zw(end) + Cs*Zc(end) + Ds*(Vc(end) - Vw(end)) + Cw*Zr(end)-Fs(end));

I offer no guarantees on the validity of the rest of your code.

clear
Mc = 401; %Weight
Mw = 48; %Wheel Mass
Ds = 2300; % Susp Damping Coef
Cs = 230000; % Susp Spring Coef
Cw = 250000; %Wheel Spring Coef
Wact = 0.001; % WActuator Time Const
t = 0; %intial Time
dt = 0.001;
Zc = 0; % Displacement Chass
Zw = 0; % Displacement Wheel
Zr = 0; %Disp Road
Vw = 0; %intial speed wheel vertical
Vc = 0; %intial speed Chassis Vertical
U=0;
alp = 0;
bet = 0;
u = U*exp(-alp*(t(end)-t(1)))*cos(2*pi*bet*(t(end)-t(1)));
Fs = 0; %leaving as 0 until we figure out the non-damp force graphing
Fs(end+1) = Fs(end) + ((Fs(end)/Wact)+(1/Wact)*u)*dt; %Damp force
Aw = 0; %intial Wheel Acc
Ac = 0; %intial Chassis Acc
 
 
while t(end) < 5
    if t(end) > 1 && t(end) < 1.11
        Zr = -0.5;
        Aw(end+1) = (1/Mw)*(-(Cw+Cs)*Zw(end) + Cs*Zc(end) + Ds*(Vc(end) - Vw(end)) + Cw*Zr(end)-Fs(end));
        Vw(end+1) = Vw(end) + Aw(end)*dt;
        Zw(end+1) = Zw(end) + Vw(end)*dt;
        Ac(end+1) = (1/Mc)*(Cs*(Zw(end)-Zc(end))+Ds*(Vw(end)-Vc(end))+Fs(end));
        Vc(end+1) = Vc(end) + Ac(end)*dt;
        Zc(end+1) = Zc(end) + Vc(end)*dt;
        t(end+1) = t(end) + dt;
        
        
    else 
        Zr = 0;
        Aw(end+1) = (1/Mw)*(-(Cw+Cs)*Zw(end) + Cs*Zc(end) + Ds*(Vc(end) - Vw(end)) + Cw*Zr(end)-Fs(end));
        Vw(end+1) = Vw(end) + Aw(end)*dt;
        Zw(end+1) = Zw(end) + Vw(end)*dt;
        Ac(end+1) = (1/Mc)*(Cs*(Zw(end)-Zc(end))+Ds*(Vw(end)-Vc(end))+Fs(end));
        Vc(end+1) = Vc(end) + Ac(end)*dt;
        Zc(end+1) = Zc(end) + Vc(end)*dt;
        t(end+1) = t(end) + dt;
    end
   
end
plot(t,Zc)

[Levi Mikesell]

Thank you so much!

[Chris]

No problem :)