Is this valuable to build such a platform?

We have to do some research on a flexible manipulator but it seems to be a total failure for the already built experiment devices. And my
adviser suggest me to create a model first on the computer, and try to do it as much accurate as possible, and make it as the real one, as a standard. And at the same time, I have to build an approximate one to carry out the control scheme, and make comparions between the 2 models, so I can assess the control scheme.
Is this reasonable?
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I am really sorry to bother you on this topic, but I am nearlly brought down to such a tricky problem, please share me some experience and guidance..
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No. Tell your advisor to do it first. If he can't do then he should be replaced. Why must the manipulator be flexible? This makes the project MUCH more difficult. Ihe design should be as stiff as possible. It can be done but not easily/cheaply. Controlling a flexible maniplator is beyond a college project. I am not saying it cant't be done. It will take too much time and effort when the correct solution is to keep the manipluator design stiff. I would fire the advisor. Show this to your advisor.
I dug up your old post http://groups.google.com/group/sci.engr.control/browse_frm/thread/e70506a4eeda5c1b/09ff3efcdc99e460#09ff3efcdc99e460 You are not ready for this. I doubt you instructor is. I can also see I missed a post where I got flamed.
Peter Nachtwey
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On Sat, 19 Jan 2008 19:21:03 -0800, workaholic wrote:

In what way?
No model can be exact; trying to make an exact model is a guarantee of failure.
No matter what you do, your model must capture the salient points of the system in such a manner that your results mean something. Most importantly, the salient points that you capture must be the _right_ ones for the question _at hand_ -- you may find yourself modeling the same system in many different ways as you try to choke various different answers out of the math.
For example, if you can create a model of the manipulator that demonstrates that it'll never work right then you shouldn't have to go any farther. Basically, if you have a (hopefully simple) model that models a better mechanism than you can ever build, and show through analysis that such a mechanism just won't work, you've shown that the upper performance bound is lower than the minimum acceptable.
Conversely, if you create a model of the manipulator that demonstrates that it can always work, you can proceed with confidence. Here you would want a (hopefully simple) model that models a mechanism that you can always better in practice, and show through analysis that the lower performance bound is acceptable.
So ask yourself (and your adviser) just what exactly you're trying to achieve with your model, and aim to make it do that, and not too much more.
--
Tim Wescott
Control systems and communications consulting
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This is true

This is pure BS and you know it.
Peter Nachtwey
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On Sun, 20 Jan 2008 02:12:54 -0800, pnachtwey wrote:

A: No model can be exact (you agreed to this). B: Failure happens when you try to do something and don't succeed (this is the commonly accepted definition, I think?)
If A is true, then no attempt to exactly model a real-world process can possibly succeed, because no model is exact.
Ergo, any try at making an exact model guarantees failure.
It's not BS, it's just a logical restatement of the original statement (with which you agree).
Fortunately we're engineers, not mathematicians, so we know (or should know) that we don't _need_ an exact model, we just need a model that's good enough.
That was my point in my original response -- if you try for an "exact" model you will fail. I have seen (and done in my younger years) attempts to make a model "exact" -- one either works on it for an indefinite period of time and then stops, or one gets a model that fits everywhere except in one's blind spots.
--
Tim Wescott
Control systems and communications consulting
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Thanks for everybody, you help me to make things clearer, since my advisor, as a mathematican, is not an expert in mechanics, who is just assigned to a task of superivising a lab doing this...
If a relatively exact model is not quite reasonable, what if I establish one on a commercial simulation platform? There are some brand new software can help to do this, however, it seems to be unacceptable by the academics.
So it seems that I have to do some theoretical research instead of this...
BTW, what the material of the Canada's Arm? Where can I get some specific information about it$B!)(BAre there any related papers?
Best regards,
Jie
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On Sun, 20 Jan 2008 23:28:06 -0800, workaholic wrote:

There's a world of difference between "exact" and "relatively exact". Getting a model that's close enough ("exact enough") for a wide range of purposes is probably doable -- but only if you start with a notion of what those purposes are, and what effects you can leave out and what you must leave in. This is _not_ something that will necessarily be successful if you just go at it in a hit or miss fashion.
I'm not sure what commercial simulation platform you're talking about. At best, a simulation tool is going to insulate you from the knowledge and experience you're supposed to be developing; at worst you'll be depending on someone else getting it right, and my experience is that where such tools don't have outright bugs they can be very poorly documented.
Whatever mathematical model you develop, it should be just that: a mathematical model. Were I your adviser I'd be looking for something of the form
x(t) = f(x(t), u(t), t), y(t) = g(x(t), u(t), t)
where x(t) is your system's state vector (hopefully it's a finite collection of discrete states), u(t) is the system's input (both command and disturbance), t is time, y(t) is the system output, f is a memoryless state evolution function, and g is a memoryless output function. You _should_ be able to describe just about any real dynamic system with the above pair of equations. Analyzing it is another problem, but you should be able to _describe_ it that way.
--
Tim Wescott
Control systems and communications consulting
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On Sun, 20 Jan 2008 23:28:06 -0800, workaholic wrote:

Another thought:
Is your adviser the only only control theorist on campus? This sort of modeling is the kind of thing that you would expect a guy with a PhD in mechanical engineering, with a specialty in control, would be able to help you out with.
In the US it would be appropriate to find out who he or she is, and show up at his/her office to politely ask for help -- then thank him/her later with a six pack of Really Good Beer. In the US a university would be considered pretty dysfunctional if no such cross-discipline help were to occur. If you're too shy, you may consider forwarding the notion to your adviser and asking if they'd do the asking for you.
--
Tim Wescott
Control systems and communications consulting
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Thanks for your guidance, I am fortunate enough to have a Ph.D student in my lab, who got a bachelor's degree in ME. But since his opinion is always reverse to my advisor's, I am not sure who's suggestion I should choose...
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It looks to me that the Phd with the ME degree, Bruce and I think this is unrealistically difficult. Tim's idea of asking for help may not work because the professors may not be able to help. I know I don't ask professor's for help. Modeling in one dimention is hard enough. Look through this use group and see how much information there is on modeling. Not much. You need to pick something to do that is outside your comfort zone but just barely. How about moving a pendulum from a over head carriage or something like that. The idea would be to get the pendulum to stop at the destination without swinging. This has practical application in crane operation.
Peter Nachtwey
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It seems that little progress have been on flexibla manipulator, since I have seen bunches of papers on IEEE journals and transactions. Much of them are aiming at such arm in one dimension.
Sometimes researchers are prone to utilize different control scheme, which is often advanced and obscure, on a different plant, instead of solving realistic questions...
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Aside from what's already been mentioned, that this project is probably unrealistically difficult, I get the impression that you may need help with setting up the project itself. That includes clearly defining the objectives, activities (including how long things will take)and resources, and structuring the whole thing as a series of linked tasks.
Your supervisor has a responsibility to guide you through this, it's something that you learn by doing. This wouldn't be the first time that I've come across supervision on academic projects that is possibly both ignorant and negligent in regard to mentoring inexperienced people in the project management aspects. If Mr C is still alive and reading this, you're a good example!!
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