# Calculate the force of a vehicle applied to a speed bump

Hello,
I am working on a project which consists in measuring the effort of a vehicle on a speed bump by implanting sensors connected to an Arduino board,
i want to use pressure sensors and i am considering putting them in the shocks but i don't know how?
do you know how? or do you have any other ideas that may help?
Thank you

An accelerometer will measure the acceleration of the vehicle as it goes over the bump. To get the applied force in N, multiply the acceleration in m/s^2 by the vehicle mass in kg.

the problem is that the force you mentioned is the sum of the forces that govern the dynamics of the vehicle, I'm not sure that it corresponds to the force applied to the speed bump.
thank you

Correct. You are facing a nontrivial problem, no matter what measuring technique you use.

Surely a set of vectors in connection with a suspension accelerometer should get you close.

I didn't understand what you mean, you can explain to me please.

Just to clarify, are you definitely interested in the force that the speed bump is subject to? And do you actually mean force, or pressure?

I ask because if this is the case, then you need the sensors on the speed bump, not the car.

I want to determine the pressure applied to the speed bump, we can also deduce it from the force, because the pressure is the force / surface.
I had thought of putting the sensors on the speed bump except that the application requires that the sensors must be installed on the car, beacause the state prohibits the placing of an object on the speed bump.

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It has almost nothing to do with the car mass and almost everything to do with the wheel mass and all suspension parts that are moving when reacting to the bump.
You would get a good measure from measuring the pressure in the tyre while it goes over the bump. Calibrate that against a laboratory setup, where you can verify the values with pressure sensors on the bump.

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Hmmm.... this does make things more complicated. The compliance of the tyre, the mass of the wheel, the compliance of the suspension, the static and dynamic friction from the dampers... all these will affect the measurements you take. Several of these variables will be non-linear, too.

I agree with the previous post: the only realistic way to achieve this will be to build your own speed bump with the necessary sensors on it. Then you would attach various sensors to the car to see if you can find a close correlation between one of them and the force sensors on the speed bump.

Once you have characterised the car in this way, then you can take measurements from a real speed bump.

Tyre pressure would seem tempting, although I don't know how you would monitor it at a high enough sample rate. An accelerometer attached to the upper or lower suspension arm would probably be the best place to start. But honestly, I do think you'll need to characterise, or "calibrate" it against a test speed bump equipped with force sensors. I bet you can find one on private property you'd be allowed to experiment with.

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do you think that the tire pressure can undergo a variation at the time of crossing on speed bump?

I think so, yes, although I bet the pressure variation is quite small. It will vary a lot from car to car, so you would still need to calibrate it against a known force and not change anything during the tests.

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ok thank you.

thank you.

Consider the approach taken in the following URL. Their focus was on response at the vehicle c.g., but you could do something similar at the wheel level. SAGE Journals: Your gateway to world-class journal research

Speed of the vehicle will impact the outcome also.

don't think different cars. there is one test vehicle.
running it at different speeds will generate data.
things that can alter the data might be temperature of the tires, the air, humidity, air pressure, etc.
but the more data you gather, the more data you have and the less speculation there is, until you find enough data that verifies the readings.

I would consider putting a tire in front of a vehicle and measuring the effects at different speeds. you could monitor the forces .

lots of data could be gathered.

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I think you need to define your parameters with a bit more accuracy.
What is the surface area you are going to divide the force by? Bearing in mind the tyre footprint shape and area are going to change as it goes over the speed bump?

Alternatively if you are going to use the area of the road occupied by the speed bump (ie a constant) (and assume the speed bump is inflexible or make a guesstimate of its "effective" area)
then really you are wanting to measure the foce applied.

The car consists of a complex system of sprung (and damped) masses with (often) 4 wheels that will encounter the speed bump at different times. And each car is different!

@DaveEvans thats a great reference!

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Well, if you are referring to the pressure applied to the speed bump, distinct from the force applied, then for a pneumatic tyre it follows that the pressure is very closely, the tyre pressure.

Because you see, that is exactly how a pneumatic tyre works!

We may be over thinking this.
If you fabricated something like a motorcycle back suspension. With momo- shockabsorber and monitored the acceleration the pressure in the shock ansorber.

You would get a lot of raw data
Monitor tire pressure in real time.
Monitor piston temperature ambient temperature, etc,etc
Do what NASA did. Put sensors on everything then put sensors on the sensors.
Once you have some sort of data you can change the test aparatus to get other data.

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