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Everything posted by DrD

Struggling with a worm gear analysis
DrD replied to edave's topic in Machine Dynamics & Design Considerations
Dear JAG, Just to be clear, all those pages are from Faires? DrD 
Struggling with a worm gear analysis
DrD replied to edave's topic in Machine Dynamics & Design Considerations
I've never really gotten into worm gearing, so I am afraid I am unable to help you. Good luck. DrD 
gear box for scissor jack design
DrD replied to edave's topic in Machine Dynamics & Design Considerations
Ian has made a good suggestion. DrD 
Bulldozing equation derivation
DrD replied to Kaustubh Sameer's topic in Machine Dynamics & Design Considerations
After a little bit more thought, I have one more suggestion (probably the best one yet!). Have you heard of an area of study called "dimensional analysis"? I'm not speaking simply of checking dimensions in your calculations, but a process to help you determine the proper form for an empirical equation. (I would not be at all surprised to learn that the equation you posted is largely empirical.) It is a technique to work from what you think you understand about a process to produce at least the form of the describing equations. One of my own teachers often said that he had made more money as a consultant using dimensional analysis that any other tool. Dimensional Analysis is closely allied with a subject called "Similitude" or "Theory of Models." It is more than I can present at this point, but it is a very powerful engineering tool. Do some web research on  dimensional analysis  similitude  theory of models I think this will get you to the answer, but not without a good bit of work. DrD 
You need to ask around to upper classmen, librarians, lab assistants, in addition to the faculty, and the main question is, "How do graduates of this school find jobs? Where do they make the necessary employer contacts?"\I I'd really be surprised if no industry recruiters come to your campus. Most schools encourage this as a way to help their graduates find work. Also, does your school offer a cooperative education (CoOp) experience? If so, take it. If you don't know, ask in the Dean's Office. My school had one, and I wish I had done it. I had never heard of such a thing, and it was only after I was long gone that I learned that it had existed. Ultimately, you have to find your own way. You know that many have done so before you and others are doing it right now. You cannot afford to be shy; you must put yourself out there, even if you find it difficult. DrD

Bulldozing equation derivation
DrD replied to Kaustubh Sameer's topic in Machine Dynamics & Design Considerations
Great question, and I really wish I could help. Sadly, this is way outside my own expertise. That said, I can offer a few suggestions. 1) If you have the book you referenced, study it really carefully, working through it line by line, equation by equation, doing all of the derivations for yourself. 2) If you do not have that book, make a real effort to get it or something else like it. Here the internet can be a huge help. I'm continually amazed at what I find. And what you find tomorrow will likely be different from what you find today. I'm not sure why this is true, but I've found it to be the case a number of times. 3) You might look in some agricultural engineering books. Tractors and other farm machinery operate on soil, and this is definitely a soil oriented problem. Good luck!1 DrD 
What did you most enjoy studying? Did you get a buzz our of thermo and heat transfer? Are you excited by machinery? What do you think you'd like to work on in the future? Your career is what YOU make of it. It can be this, or it can be that, or perhaps it can be the other. YOU have to choose which direction you want to go, and then make the necessary inquiries as to how to get there. Talk to the faculty, talk to any company representatives that come to campus to interview graduates, talk to everyone you can. I have no idea what the opportunities are in your location, but there are folks who do know. Ask them. DrD

With no question, it is not possible to help you. DrD

Posting twice, an hour apart, is a bit of overkill. DrD

I recommend that you choose the area where you think you are best. I know what I would choose, but that is irrelevant to your choice. DrD

How do I calculate point load failure for various distances?
DrD replied to TragicWarrior's topic in Engineering Materials
You might start by calculating the bending stress for the known case with the load at the middle. Unfortunately, all you know is that this stress is too much. The pipe might also fail with a 90 lb load, but you have no way to know. Consequently, you only know a value too high, but you need the maximum load that does not cause failure. If somehow you come up with a max load that avoids failure, then you can define a failure maximum stress. Then you could calculate the bending stress for the load at an alternate position and compare that to the known max safe value. DrD 
Please see my answer to your previous note. DrD

Dear Fatima, The only places where I am likely to be able to help you are Theory of Machines, Vibrations, Dynamics, Machine Design, and Numerical Methods. As a start, I suggest you download a copy of my textbook, Mechanics of Machines, Ver. 2.1, available here at the ME Forum (I'm not sure where they have put it now) or at Academia.edu or at Mekanizmalar.com. I think you may find a lot of interesting material in there. Also, write to me as you have here with other questions. DrD

Why You Shouuld NOT Use the D'Alembert's Principle
DrD commented on DrD's blog entry in Mechanics Corner
Double Wow!! The number of cursory lookers has more than doubled, and the number serious enough to open the PDF is all the way up to 16!! Just wow!! DrD 
Timing belt drive system
DrD replied to Manikandanmech's topic in Machine Dynamics & Design Considerations
When you say you want faster response, I presume you mean you want a quicker motion at the load. You don't show any load on the intermediate (idler) shaft, so I will assume that there is none. The answer is not entirely simple, but there are two factors to consider. (1) How much inertia is involved in the system? (2) How stiff is the system? Both systems have nearly the same amount of belt inertia, but the three shaft system definitely has more inertia due too the double pulley and idler shaft. This works to slow the system response. In terms of stiffness, it is difficult to say. It depends upon the axial stiffness of the belts involved. I suggest that you make a mathematical model of both systems, get some actual numerical values for the parameters, and see which one has the better response. DrD 
Timing belt drive system
DrD replied to Manikandanmech's topic in Machine Dynamics & Design Considerations
Are you talking about two belts side by side between the same two shafts, or are you talking about three shafts connected by two belts? An intelligent answer is not possible without a clear question. A figure would help. DrD 
Your drawing seems to imply the magnet on the stationary part and the winding on the moving part. Do yourself a favor and reverse those two items. Then you will not have to pass winding current onto a rotating element. Better yet, rather than reinvent the wheel, buy a book on motor design and discover what is already well known. Might not be as much fun, but if you are serious about this, it will lead to much better results. DrD

So what is the point? We have a gripper, but aren't grippers fairly common? DrD

You might want to consider an animal powered drive. I'm thinking of a horse or mule walking in a circle or something similar. DrD

Binomial and Taylor expansion of differential Equations
DrD replied to G B Reid MIMechE, SIMarEST's topic in Ideas
I'm pretty familiar with variational methods, but I'm not quite clear about what you want. Can you cast your question in the context of a specific problem, perhaps? If not, shoot me a PM and we'll talk. DrD 
Why You Shouuld NOT Use the D'Alembert's Principle
DrD commented on DrD's blog entry in Mechanics Corner
Wow! 60 people looked at the introduction, but only 10 bothered to download the file. I really should learn that nobody cares. DrD 
There is a major question as to how the two vertical supports are attached to the boxes. Are these simple supports, or is the support rigidly attached to the box so as to transfer a moment between the support and the box? Is the lower end of the support embedded in the ground, or is it simply attached? I think your drawing is incomplete in that these matters are not clear. The question cannot be addressed without this information. Also, why do you label the figure backwards from t he picture with respect to left and right? DrD

Mechanics Corner #50 A Journal of Applied Mechanics and Mathematics by DrD Why You Should NOT Use the D'Alembert's Principle I think it is safe to say that every engineering student studies both Statics and Dynamics. We are told that Statics is easier than Dynamics, which is often true but not so in all cases. When we get to Dynamics, many teachers, particularly physics teachers, will urge the use of something called D'Alembert's Principle. They tell us that it reduces dynamics problems to statics problems and thus makes life so much easier. This is a lie! It just is not true!! For an extended discussion about why this is the case, read on please. NoDAlembert.pdf

Dear All, For any of you who may have read my previous post on this question, I have to tell you that it has an error. I left out the tangential forces on the fluid element, and thus got a wrong result. I hope to have a better result for you in a few days, but for now, do not make any use of the result posted earlier. Sorry about that! DrD