Trouble calculating Acceleration from given velocity vector.

I want to create a for loop to use the iterative formula for acceleration using given velocity values:

ai = (vi+1 - vi) / dt

I have tried repeatedly but am new to MATLAB. I used the following:

a = diff(V)/diff(T)

where V is velocity and T is time

but the acceleration vector is then 1 smaller than I want to be able to plot the graph a,T

forgive my poor syntax, I am very new to MATLAB

In summary, I need to calculate Acceleration and keep it in the same vector size as Time in order to plot these, not one value smaller.

[darova]

Can you attach an example code? Your code?

[Connor Watkins]

%Data was imported as a table using the import wizard, found in the home section.
A = readtable('Log_U0006387_160311_740d0(1).csv');

%% Electric Vehicle Performance

%Starting by extracting each data set from the table
%Converting where necessary immediately to avoid mess
Time = A{:,1};              %Time in seconds
Speed = A{:,3}*1.60934;     %Speed in KpH
Gear = A{:,142};            %Gear used
Elevation = A{:,2}/3.281;   %Elevation in metres
SOC = A{:,5}/10000;         %State of Charge in '%'
PackVolts = A{:,7};         %Battery Voltage in Volts
PackAmps = A{:,8};          %Battery Current in Amps

%Plotting the graphs
%First I create my subplot figure, with 6 rows and 1 column
subplot(6,1,1)
plot(Time, Speed, 'r'), xlabel('Time (s)'), ylabel('Speed (kph)') %I then plot Speed against Time in pos. 1
%Then I create the second subplot, being Gear over Time
subplot(6,1,2), plot(Time, Gear, 'b'), xlabel('Time (s)'), ylabel('Gear')
%Third subplot - Elevation over Time
subplot(6,1,3), plot(Time, Elevation, 'magenta'), xlabel('Time (s)'), ylabel('Elevation (m)')
%Fourth subplot - State Of Charge over Time
subplot(6,1,4), plot(Time, SOC, 'Yellow'), xlabel('Time (s)'), ylabel('SOC (%)')
%Fifth subplot - Battery voltage over Time
subplot(6,1,5), plot(Time, PackVolts, 'g'), xlabel('Time (s)'), ylabel('Voltage (Volts)')
%Sixth subplot - Battery Current over Time
subplot(6,1,6), plot(Time, PackAmps, 'cyan'), xlabel('Time (s)'), ylabel('Current (Amps)')

%%Power Consumption
%Data Extraction
MotorPwr = A{:,133}/10; %Motor Power in kW
AuxPwr = A{:,134}/10; %Auxillary Equipment Power in kW
ACPwr = A{:,135}/5; %Air Conditioning in kW

%Battery Power Calculation

BatPwr = PackVolts.*PackAmps/ 1000; %Power in Watts

%Powers against Time Plot 
figure (2)
plot(Time, MotorPwr, '-.r')
grid on
title('Motor, Auxillary, A/C and Battery Power over Time')
hold on 
plot(Time, AuxPwr, ':k')
plot(Time, ACPwr, '--b')
plot(Time, BatPwr, 'g')
hold off
xlabel('Time (s)')
ylabel('Power (kW)')
legend('MotorPwr','AuxPwr','ACPwr','BatPwr')

%% Acceleration and Driving Styles
%Converting speed into metres per second

V = Speed.*1000/3600 ;
a0=;  %Similarly to given equation, Delta V/ Delta T = A in m/s^2
if a <0
    a=inv(a);   %To receive positive values for acceleration
end
%If statements for the Driving Style Mapping 
if a >= 0.7
    ds_mapping = 1;
elseif a <= 2.81
    ds_mapping = 2;
elseif a <= 3.65
    ds_mapping = 3;
else
    ds_mapping = 0;
end

The bottom section (Acceleration and Driving Styles section) is the area which is giving me trouble

[Saad Hussain]

Hey i was wondering if you still have your code file saved to this assignment and you can send me? ive got a similar one

Answer 1

[darova]

So what about this formula?

a = diff(V)/diff(T)

Just forgot about ./ element-wise operator

a = diff(V)./diff(Time);

Then use for loop

ds_mapping = a*0;
for i = 1:length(a)
    if a(i) >= 0.7
        ds_mapping(i) = 1;
    elseif a <= 2.81
        ds_mapping(i) = 2;
    elseif a <= 3.65
        ds_mapping(i) = 3;
    end
end

What are trying to do here? You want absolute value ?

if a <0
    a=inv(a);   %To receive positive values for acceleration
end
% a = abs(a);

Note: once you used diff you have one element less (because it calculates difference v(i+1)-v(i))

[Connor Watkins]

I'm trying to plot a graph of acceleration over time, which means I need to increase the size of the accceleration vector back to the Time vector size. I then want the if statement to deduce values for driving style (either 1, 2, 3 or 0) based on acceleration so that I can plot that over the top of the acceleration.

At the minute, the ds_mapping only receives one value which is 0.

Thank you for you help so far by the way, appreciate the response :)

[darova]

• I need to increase the size of the accceleration

Or you can plot without first value

plot(Time(2:end),a)

a(i) can be greater 0.7 and less than 2.81. What then?

if a(i) >= 0.7
elseif a <= 2.81

[Connor Watkins]

a(i) can be greater 0.7 and less than 2.81. What then?

the idea was that the other 'elseif's would cover what would happen in those circumstances. So if the value was above 2.81 but below 3.64 then its ds_mapping = 2, higher than 3.64 but lower than 6.5: ds_mapping = 3 and if it doesnt apply to any of these, the ds_mapping is zero.

I tried using && to allow me to have multiple conditions for each if statement "if a <=0.7 && a >= 2.80" for instance, but it didnt seem to like the use of && or ||.

thank you for the suggestion of plotting Time from 2:end instead of the whole vector. I didn't think of that