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# From Angular Velocity to rpm

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### #1jujunosuke  Members   -  Reputation: 188

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Posted 20 April 2012 - 03:41 AM

Hi all,

In my car simulation i have change a lot of settings and i am trying a new approach.
I try to simulate an Engine and then get the resulting speed of the wheels.

Here is what i have done so far, but i don't think that my engine_rpm calculation is correct..
I try to calculate it from the engine angular velocity.

var maxTorque = getTorqueCurve( getRPMEngine() ); //This function return a Torque at a given rpm ( rpm minimum is 1000 )

engineAngularAcceleration = maxTorque / getCylinderInertia( 1000, 0.5 );
engineAngularVelocity += engineAngularAcceleration * TIME_STEP;

var rps_engine = engineAngularVelocity * Math.PI * 2;
rpm_engine = rps_engine * 60;


Any help to clear this out would be welcome.
Thank you very much.

### #2Álvaro  Crossbones+   -  Reputation: 17464

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Posted 20 April 2012 - 07:42 AM

What seems to be the problem? Do you have an example of a situation where that code produces a clearly absurd output?

And why did you call that variable maxTorque'? Isn't it just torque'?

### #3kunos  Crossbones+   -  Reputation: 2245

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Posted 20 April 2012 - 08:59 AM

To convert from rad/s to rpm this is the macro I use:

So ya, your calculation is wrong.

### #4Álvaro  Crossbones+   -  Reputation: 17464

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Posted 20 April 2012 - 12:00 PM

kunos is right:

var rps_engine = engineAngularVelocity * Math.PI * 2;

should be

var rps_engine = engineAngularVelocity / (Math.PI * 2);

### #5jujunosuke  Members   -  Reputation: 188

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Posted 22 April 2012 - 07:18 PM

What seems to be the problem? Do you have an example of a situation where that code produces a clearly absurd output?

I don't have totally strange output but, any wrong calculation will lead to wrong simulation of course...

And why did you call that variable maxTorque'? Isn't it just torque'?

Yeah, This is just an example, in fact, i have some previous calculation with the variable torque, but anyway..

Thank you Kunos my master !
And thank you alvaro.

I really appreciate both of your help !
Thanks again !

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