Questions about the Performance-Box.

[karabiner98k]

1) How can a Performance-Box calculate power at the wheels (and at the flywheel) by just knowing the weight of car?


PerformanceBox - Datalogger and Performance Meter

2) Can it measure acceleration of speeds more than 300km/h? (for example 0-350km/h)

[Matra et Alpine]

1) application of physics ..... By knowing acceleration of a known weight you can calculate the power. The GPS provides acceleration measurement - SO accuracy of power is dependant on quality of GPS signal and device.
Power at flywheel is by applying a "fudge factor" to account for losses in the drivetrain.

2) GPS-based meters are limited by the update rate and accuracy of the GPS receiver.
10 per second is reasonable for consumer use and no reason for an upper speed limit.
The device specs will give limits though as software processing may limit it.

[karabiner98k]

1) application of physics ..... By knowing acceleration of a known weight you can calculate the power. The GPS provides acceleration measurement - SO accuracy of power is dependant on quality of GPS signal and device.
Power at flywheel is by applying a "fudge factor" to account for losses in the drivetrain.

Thanks.
But i want to know how it calculates?
It certainly uses some formulas to calculate power.
I want to know those formulas and calculations.

[karabiner98k]

1) application of physics ..... By knowing acceleration of a known weight you can calculate the power. The GPS provides acceleration measurement - SO accuracy of power is dependant on quality of GPS signal and device.
Power at flywheel is by applying a "fudge factor" to account for losses in the drivetrain.

Thanks.
But i want to know how it calculates?
It certainly uses some formulas to calculate power.
I want to know those formulas and calculations.

[drakkie]

Thanks.
But i want to know how it calculates?
It certainly uses some formulas to calculate power.
I want to know those formulas and calculations.

You have Matlab? I can send you some M-files with all the calculations needed (school assignment)

[karabiner98k]

You have Matlab? I can send you some M-files with all the calculations needed (school assignment)

No. i don't have it. What is it?
I think it is a kind of language for computing.
Could you explain?

[Matra et Alpine]

Google is your friend

for 1/4 mile terminal speed measurement http://media1.ajdesigner.com/horsepower_trap_speed.swf

loads of them out there

If you want to go at it from math principles Car Acceleration Calculator will help ( or blow your mind dependant on how you are at calculus )

[Alastor]

Thanks.
But i want to know how it calculates?
It certainly uses some formulas to calculate power.
I want to know those formulas and calculations.

The GPS calculates changes in position and time. So basically the GPS can measure change in distance and change in time and using that information you can find the following:

Velocity = 'Change in Distance' / 'Change in Time'
Acceleration = 'Change in Velocity' / 'Change in Time'

Force = Mass * Acceleration [Mass is the vehicle weight you have to enter]

Power = Force * Velocity

In summary the GPS calculates velocity and force (where the force depends on the vehicle weight) and from those quantities power can be estimated.

[susane]

Hey this is all that we learn t in the school,in our science theory hope you remember force x mars =acceleration this is the same kind of language to measure the speed .
Cheap Volkswagen Parts

[drakkie]

No. i don't have it. What is it?
I think it is a kind of language for computing.
Could you explain?

It's a scientific mathematic programme we use very intensive to calculate almost everything on a vehicle.

The GPS calculates changes in position and time. So basically the GPS can measure change in distance and change in time and using that information you can find the following:

Velocity = 'Change in Distance' / 'Change in Time'
Acceleration = 'Change in Velocity' / 'Change in Time'

Force = Mass * Acceleration [Mass is the vehicle weight you have to enter]

Power = Force * Velocity

In summary the GPS calculates velocity and force (where the force depends on the vehicle weight) and from those quantities power can be estimated.

What might be nice to add is the way to calculate the resistances on a vehicle. When the sum of all resistances is larger than the torque on the wheels provided you are at top speed.



This graph shows you the resistances I calculated for my own car, a Ford Puma. As you can see I calculated the total resistance of the vehicle (F_Tot_s in this graph), the rolling resistance (F_rol) and air resistance(F_lucht). Now how is this calculated. I will start of with the air resistance:

F_air = 0.5 * rho * v^2 * A * C_d

rho = The density of air (1.293 kg/m^3)
v = velocity
A = frontal surface of the vehicle
C_d = drag coefficient

Now the velocity, air density and drag coefficient are usually a known value or can be found. The frontal surface is quite complex to calculate so we usually take a estimated value.

Next up is the rolling resistance. This is best explained I think by the pretty good Wikipedia article found here:
[ame="http://en.wikipedia.org/wiki/Rolling_resistance"]Rolling resistance - Wikipedia, the free encyclopedia[/ame]



Above is the theoretical power (P) and torque(M) of my car. In reality it differs slightly, but it's a bit hard to calculate the effect of Variable Cam Timing, besides it wasn't needed for the assignment anyway..



The above graph shows you how much power is needed and available for accelaration. I now notice I have the numbers on the y-axis a bit wrong, but it's about the general picture anyway. So what we see here is that the power needed for acceleration increases with the speed. The power available decreases because of the resistances of the vehicle, until it reaches 0. At 0, you reach the top speed.

It's getting pretty damn late, so I will finish this off tomorrow. Feel free to add something or correct this years old assignment guys!