I need help to figure out how to turn acceleration data into Horsepower/Torque


by soundengineer
Tags: horsepower torque
soundengineer
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#1
Dec19-08, 01:01 PM
P: 33
I have a vehicle with some known info...
weight: 3400lbs
Speed at a specific time: see data in chart linked below
overall gear ratio: 2.922
Tire size: 25.68 inch Radius
RPM at speed: see data in chart linked below

heres the data
Acceleration Data via Google Documents

where do I start??
I dont mind doing math....but I need some help understanding what I need to do and where I need to start.

I probably want to do this over a 1 second sample so that I dont have to do any x1000 or /1000 math in there...
I can convert the speed into Kph and the mass I can do in kg if it makes it easier

I hope to come up with a basic understanding of the math involved and do a little chart of Horsepower and torque vs RPM in the end
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buffordboy23
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#2
Dec19-08, 02:08 PM
P: 540
I tried to a car analysis at one time. Here is a link with a lot of formulas:

http://www.rdrop.com/~/larry/download/formulas.pdf

See if this helps. I couldn't see your car data.
soundengineer
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#3
Dec19-08, 03:31 PM
P: 33
Quote Quote by buffordboy23 View Post
I tried to a car analysis at one time. Here is a link with a lot of formulas:

http://www.rdrop.com/~/larry/download/formulas.pdf

See if this helps. I couldn't see your car data.

not really...I can find all of those formulas and I understand them on their own....
its making them work together to get my formula here...

I know the mass and I know that it accelerates a certain amount over a given time....
how do I calculate horsepower for that given time...
I can set it at 1 second or 10 seconds....I dont care about teh interval...al I want to know is how to get from acceleration of 12mph in one second to horsepower value for that tme

buffordboy23
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#4
Dec19-08, 04:11 PM
P: 540

I need help to figure out how to turn acceleration data into Horsepower/Torque


Did you try looking for any dyno chart data for your stock vehicle online? This could simplify your task tremendously.

I'll take a better look at your question when time permits.
berkeman
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#5
Dec19-08, 04:19 PM
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Quote Quote by soundengineer View Post
not really...I can find all of those formulas and I understand them on their own....
its making them work together to get my formula here...

I know the mass and I know that it accelerates a certain amount over a given time....
how do I calculate horsepower for that given time...
I can set it at 1 second or 10 seconds....I dont care about teh interval...al I want to know is how to get from acceleration of 12mph in one second to horsepower value for that tme
If you know the acceleration and mass, you know the force. If you know the force and distance, you know the work. If you know the work and time, you know the power. And 1hp is about 750W (I don't remember the exact conversion). Does any of that help?
buffordboy23
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#6
Dec19-08, 04:26 PM
P: 540
Acceleration of the car is caused by a force. When the force acts over a certain distance it does work. If you assume that the acceleration is constant, then the force is constant: force = mass x acceleration. When you accelerate your car and it moves over a distance d, work is done: Work = force x distance and has units of joules (energy). Now, it takes your car some amount of time to traverse this distance. Power is the rate at which work is applied: power = work / time and has units of joules per second (or watts). Horsepower conversion: 1 hp = 750 watts (approx.).

Don't forget that the car has to overcome numerous frictional forces so this may complicate your analysis.

Does this give you a better idea?
swraman
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#7
Dec19-08, 04:30 PM
P: 145
I did this for a math experiment to test horsepower of cars and compare them to manufacturers data.
I fitted a curve to the data as a function of time, then used that as position function x(t). from there there are many ways to get to power as a function of time; remember a car's power changes with time (it is not constant).
soundengineer
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#8
Dec19-08, 07:09 PM
P: 33
Quote Quote by buffordboy23 View Post
I tried to a car analysis at one time. Here is a link with a lot of formulas:

http://www.rdrop.com/~/larry/download/formulas.pdf

See if this helps. I couldn't see your car data.

I re-did the URL
you should be able to see it now....I forgot to put it in share mode
soundengineer
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#9
Dec19-08, 07:20 PM
P: 33
Quote Quote by buffordboy23 View Post
Acceleration of the car is caused by a force. When the force acts over a certain distance it does work. If you assume that the acceleration is constant, then the force is constant: force = mass x acceleration. When you accelerate your car and it moves over a distance d, work is done: Work = force x distance and has units of joules (energy). Now, it takes your car some amount of time to traverse this distance. Power is the rate at which work is applied: power = work / time and has units of joules per second (or watts). Horsepower conversion: 1 hp = 750 watts (approx.).

Don't forget that the car has to overcome numerous frictional forces so this may complicate your analysis.

Does this give you a better idea?


I get this......
I just have a hard time with understanding the units
force = mass x acceleration
what units are force?
is mass LBS or KG
what is the acceleration unit?

so work(joules) = (mass x acceleration) x distance

how can I get the distance? tire diameter math and speed correct?
and does that need to be in inches? feet? meters?

so...Power(watts) =((mass x acceleration) x distance) / time(in seconds?)
and that whole thing...
watts * 0.00134102209 = Horsepower
or watts / 745.699872 = Horsepower


am I correct in the math formula??
if yes..then I just need help with the units of measure being used in my variables
Saladsamurai
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#10
Dec19-08, 07:28 PM
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Force should be in Newtons or pound-force. You need to get the mass of your car instead of weight. I would go with metric units for now. Covert your weight to Newtons and then divide by local gravity 9.81 m/s2 should be fine.
soundengineer
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#11
Dec19-08, 07:40 PM
P: 33
Quote Quote by Saladsamurai View Post
Force should be in Newtons or pound-force. You need to get the mass of your car instead of weight. I would go with metric units for now. Covert your weight to Newtons and then divide by local gravity 9.81 m/s2 should be fine.
so my mass should be
3400 * 4.4482216 = 15123.95344 newtons / 9.81 = 1541.6874046890927624872579001019
rounded = 1541.6874 (what unit???)

and what about the acceleration part...
what formula is my acceleration? and what are my units for acceleration?
Saladsamurai
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#12
Dec19-08, 07:48 PM
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mass=kgs
acceleration should be in meters per second squared. But you do not have acceleration, you have the vehicles speed (or velocity) at various times.

You need to come up with a formula or function that relates the sample velocities to time.
soundengineer
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#13
Dec19-08, 07:57 PM
P: 33
Quote Quote by Saladsamurai View Post
mass=kgs
acceleration should be in meters per second squared. But you do not have acceleration, you have the vehicles speed (or velocity) at various times.

You need to come up with a formula or function that relates the sample velocities to time.
so could I have just done

1 pound = 0.45359237 kilograms (google)
and taken 3400lbs * 0.45359237 = 1542.214058 kilograms
even though it doesnt quite match up to the previous math 1541.6874 kg?

as far as the acceleration...
difference in velocity over difference in time ? correct??
this formula just popped back in my head...
so (dV2-dV1)/(dT2-dT2)
velocity in meters/second and time in seconds
which gives me the acceleration in m/s^2


so...Power(watts) =(([mass_in_kg] x [(dV2-dV1)/(dT2-dT2)]) x [meters_traveled]) / time(in seconds)
Saladsamurai
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#14
Dec19-08, 08:24 PM
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Looks pretty good to me. (dV2-dV1)/(dT2-dT2) will get you the average acceleration and hence the average force and hence the average power.

You might be able to get a better approximation of acceleration by plotting a portion of your data in excel and finding a regression line and then using that to find the work done. But, that is only if you want to.
soundengineer
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#15
Dec19-08, 08:40 PM
P: 33
Quote Quote by Saladsamurai View Post
Looks pretty good to me. (dV2-dV1)/(dT2-dT2) will get you the average acceleration and hence the average force and hence the average power.

You might be able to get a better approximation of acceleration by plotting a portion of your data in excel and finding a regression line and then using that to find the work done. But, that is only if you want to.
I was planning on that :)
I have plans on using the data to solving for horsepower in vehicles at the dragstrip...
lets me know if the vehicle is running it tip top shape or if we need to adjust some things to get a little more power out of it..
we know what it does at its best...and we know what to adjust to compensate for various weather/climate conditions to get back to that....we've only figured that stuff out from the dyno....if we can come up with a dyno on the dragstrip then we can run a better race

one thing I dont get
Power(watts) =(([mass_in_kg] x [(dV2-dV1)/(dT2-dT2)]) x [meters_traveled]) / time(in seconds)

what is my bold type time in seconds?
where do I get that value?
Saladsamurai
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#16
Dec19-08, 08:54 PM
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I believe that should be the same time as used in the formula for acceleration. Think about it, you want to know how much Work (Force*displacement) this thing does PER second (Power). So if your force was calculated over a certain time interval (and then work with a corresponding distance interval) than you need to divide that work by THAT time interval to get Power over that interval.
soundengineer
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#17
Dec19-08, 09:04 PM
P: 33
Quote Quote by Saladsamurai View Post
I believe that should be the same time as used in the formula for acceleration. Think about it, you want to know how much Work (Force*displacement) this thing does PER second (Power). So if your force was calculated over a certain time interval (and then work with a corresponding distance interval) than you need to divide that work by THAT time interval to get Power over that interval.

so a recap to make sure this is right

((([mass_in_kg] x [(dV2-dV1)/(dT2-dT1)]) x [meters_traveled]) / [(dT2-dT1)seconds])* 0.00134102209 = Horsepower

Torque = (Horsepower x 5252)/RPM

then I can plot them both in excel and do some comparisons :)
soundengineer
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#18
Dec19-08, 09:53 PM
P: 33
ok...so I think I did some bad math somewhere...
seconds/rpm/mph/gear/dv/dt/distance/HP
7.52 3551 22.37 2.922 0.62 0.07 0.65 0.83
7.65 3605 22.99 2.922 0.62 0.13 1.34 1.71
obviously my HP math is wrong somewhere


=(((3400*0.45359237)*(DV/DT)*Distance)*DT)*0.00134102209


I also re-updated the Data in the google documents page
you are looking at data in line 10/11


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