order od system

Hi ,
I am bit confused in answering the following question, although it is very basic.
Can we predict the number of masses in the system from the order of the
characteristic equation developed by identifying the step response of the system?
or
if a system has 4 masses then how much would be the order of the system?
Looking for urgent reply,
bye
Zia
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virtualthinking wrote: ...

That depends on how they are connected and on the compliances.
Jerry
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Jerry Avins wrote:

And what your inputs and outputs are (i.e. with a single mass, force input and velocity output the order = 1, not 2, at least until someone asks how you're measuring velocity).
Any real system, of course, is of infinite order. The question isn't "what is that system's order?", the question is "what order should I assign to that system for the problem at hand?".
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Tim Wescott
Wescott Design Services
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Hi,
well thanx for quick replies.
Well I am doing the system identification of the electrical power steering system( with double pinion, pinion and rack assembly from ZFLS), with steering wheel angle as input and Wheel steering angle as output.
Both of them are angles.
After identification of the system by SID and LS method , I have found a 4th order (order of characteristic equation) arx model for the system satisfying to input and outputs. Now I am in fix well how can I describe the system interms of masses approx. whether this would be a 4 mass system( masses means inertial masses ) or more or less. (in terms of simplified modelling or reduce order modelling).
I have an idea of representing the system by 4 inertial masses, Tyres, rack, pinion and column assembly, motor( residing on the rack), and all connected in series. As pinion and column assembly could be transformed to the rack side.
So my last questions were from this. Now how can estimate approx. no. of masses involved ?
Regards,
Zia
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virtualthinking wrote:

I would try to make some intelligent guesses about what the actual mechanics of the system are, and see what I needed to do to make the models line up. A 4th order system is most likely two masses and two springs, but the exceptions occur often enough that you can't count on it.
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Tim Wescott
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virtualthinking wrote:

Assuming that the tie rods and car frame are rigid enough, both wheels and their linkages form basically a single mass for purposes of analysis. There will be a slight nonlinearity from the geometry of the Ackerman steering, but that won't count for much.
Jerry
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