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Beyond velocity and acceleration: jerk, snap and higher derivatives (2016)

(iopscience.iop.org)
181 points EndXA | 1 comments | 19 Jun 24 10:16 UTC | HN request time: 0.243s | source
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londons_explore ◴[19 Jun 24 11:39 UTC] No.40727286[source]▶
I wish designers of vehicles - particularly cars, trains and busses, would work to minimize jerk, snap and crackle.

Turns out if you minimize those, you get a far more comfortable ride. It matters far more than acceleration.

Finite element models of the whole system (tyres and suspension components and flexing elements of the vehicle body and road/track) can quickly allow analysis of the jerk, snap and crackle, and allow tuning of damping and drive system control loops to make a far more comfortable ride.

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constantcrying ◴[19 Jun 24 13:19 UTC] No.40728030[source]▶
>I wish designers of vehicles - particularly cars, trains and busses, would work to minimize jerk, snap and crackle.

They do.

>Turns out if you minimize those, you get a far more comfortable ride. It matters far more than acceleration.

They know that this is the case. And put a lot of effort into making sure your car has the desired feel.

Besides your comfort these considerations are extremely important for the durability analysis for the vehicle.

>Finite element models of the whole system (tyres and suspension components and flexing elements of the vehicle body and road/track) can quickly allow analysis of the jerk, snap and crackle, and allow tuning of damping and drive system control loops to make a far more comfortable ride.

Finite element simulations are undesirable, they are extremely calculation expensive for those kind of large models and somewhat unsuitable. They are used in crash tests.

For the application you described multi body systems are used, where the car is decomposed into its functional components, which can be modeled either as stiff or flexible. With that you have a reasonably accurate model of a car which you can use to test on a virtual test track.

Basically every competent car manufacturer is doing this.

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amelius ◴[19 Jun 24 15:52 UTC] No.40729433[source]▶
I have two questions:

1) does this hold for all 3 of jerk, snap and crackle, like OP suggested?

2) In applications where no humans are involved (robot actuators etc.), would it make sense to minimize jerk, snap and crackle too?

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1. constantcrying ◴[19 Jun 24 16:19 UTC] No.40729695[source]▶
>1) does this hold for all 3 of jerk, snap and crackle, like OP suggested?

They aren't the fundamental quantities you would look at, typically the output of a multi body system are displacement/velocity/acceleration, but of course if you look at a plot of acceleration you can just see these quantities (at least the first and second derivative are quite easy to see) or calculate them. And of course the ride comfort is related to the smoothness of the forces you experience, which is the same as wanting to minimize the derivatives of force. But I would suggest that these quantities are quite hard to analyze quantitatively as they are, naturally, subject to far more noise.

Where these quantities definitely are considered is when you look at vibrations.

>2) In applications where no humans are involved (robot actuators etc.), would it make sense to minimize jerk, snap and crackle too?

Yes, if you care about durability. Parts can break for different reasons, intuitively you easily understand that exceeding certain loads breaks them. Another, far more insidious, failure case is a cyclic load, which never exceeds a particular threshold. Again, vibrations play an important role there.