DrD

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Everything posted by DrD

  1. "

     

    "I think the human race made a big mistake at the beginning of the industrial revolution, we leaped for the mechanical things, people need the use of their hands to feel creative." - Andre Norton"

    Feel free to reject all the products of the industrial revolution in your own life. Do not ride in automobiles, do not use electricity, do not use any machine of any type, and of goodness sakes, do not use a computer. Just go live in a cave or a mud hut, (no lumber, nails, screws, or glue allowed), burn only wood or cow chips, and do not eat anything cultivated or processed by machinery. This would be a good start, and then I'm sure you will find ways to improve on this beginning. Enjoy your life!!!

    DrD

  2. The fact that it offers a high gear ratio is certainly an advantage, but that can also be achieved by other mechanisms. The major reason is that, under most circumstances, the worm drive can not be back driven. This is a major safety consideration for a hoist. DrD
  3. With regard to materials, you must stay away from most metals, and especially aluminium. They will corrode rapidly in a salt water environment and lose strength accordingly. Think more of polyesters and epoxy materials. Are we to understand that rotation is in a horizontal or vertical plane? Assuming a horizontal plane for the rotation, you will need an airfoil shape, as the turning force is developed by hydrodynamic forces. Where will you generate power, below the water or above? This is a difficult problem, one that I worked on for the US Navy some years ago. You have a lot of hurdles to face to get this to work. DrD
  4. The flywheel does not store force; it stores kinetic energy. This is the source of energy to keep the crank turning during the compression strokes when the cylinder pressure is retarding crank rotation. Imagine that you start a small, single cylinder engine, such as a lawnmower engine, With the lawnmower blade in place, the engine runs just fine, but in many cases if you remove the blade, the engine will not run at idle speed. Why? Because the blade acts as a part of the flywheel, storing energy for the compression stroke. If you remove the blade, there may not be enough energy stored to complete the compression stroke. DrD
  5. In the early designs, the needle was actually attached tot he edge of a metal diaphragm. This caused the diaphragm to move with the needle, thus driving the air column. The horn is simply a motion amplifier (get a book on acoustics to study this). If you want to go electronic but still preserve the appearance of the older style, you might place a very small speaker at the small end of the horn, and let the horn do the rest. DrD
  6. Is P the number of planets, or the number of teeth on a planet gear? If it is the number of planets, I don't think it is true at all; at least, I do not see it. DrD PS: Remember that, for gears that actually mesh, the number of teeth on the two gears are each proportional to the pitch radii of the gears.
  7. I"m glad to hear that you found something useful, Tim. It is almost comic that the name is FreeCAD, but it costs $10. I wonder what it would cost if it were called PayForItCAD? DrD
  8. Look for an opportunity in a company that actually manufactures some product. Such an employer will usually lket you see the whole process, from design, through manufacturing engineering, to sales and service. This is particularly valuable for a student. Do not go to a company that only does paper studies or the like; this is not the whole picture. DrD
  9. Set Gyi said, "Magnetic." Is this a statement, or a question, or something else? What is the points here? DrD
  10. The first question is not fully defined. You are told how far the lift is to travel in the specified time, but nothing is said about the acceleration profile required. We should probably assume that the initial velocity is zero, as is the final velocity. But what is undefined is just how acceleration will vary during the 40 second interval. Without this, the problem cannot be answered. For the second question (assuming that you have somehow managed to solve the first one), you need to separate the total gravity load into the dead load of the lift structure plus the live load of the people. For the third question, this is a simple application of Sum F = m*a, while carefully attending to the signs of all terms. This is not hard, at least not if you are really an engineer. DrD
  11. Many years ago, I disassembled a crank powered gramophone. This was a commercial model, made in the USA in the 1920s, I think. Let me tell you what I found. 1. There was a large main spring for storing the energy applied by the crank. This lets the user crank briefly, then enjoy continuous play without cranking for several minutes. However, a mainspring alone will not give a constant speed, but rather will apply a high torque when initially tightly wound, resulting in a high speed, and then will slow down as the torque is reduced. 2. There was a governor, the sort of mechanism known as a "fly-ball governor" that regulated speed. When the shaft speed is too high, the fly weights move out, and when the speed drops too low, the weights move in. Most fly-ball governors operate on a vertically oriented shaft, so that gravity provides the return action. In my gramophone, the shaft was horizontal, and the balls were pulled toward the shaft by leaf springs. 3. There was a simple friction brake actuated by the fly-ball governor. When the weights moved out due to overspeed, a simple linkage applied a non-rotating "shoe" to the side of a rotating disk on the main shaft; this would cause the shaft speed to drop due to the extra friction. As the shaft torque from the spring was gradually decreased due to unwinding, the shoe would contact the disk ever more lightly. The overall effect was a very good approximation to constant speed. 4. There was a gear train to give the required spindle speed, not necessarily the speed of the governor shaft and brake system. I hope that this helps. If you have any success, or want to discuss more details, I hope you will post a note to let us know how you are getting on with this projects. DrD
  12. There is no such thing as a "curved rack." By definition, a rack is straight. It appears that what you intend is a sequence of racks and gear segments, joined in such a way as to present a continuously running tooth profile. Looked at in this way, I don't think it will be too difficult. You simply need to assure continuity of the tooth profile at the joints. DrD
  13. So, ..... when are you going to post some more? Or did you think that this exhausts the field? I'm feeling all brushed up, at least to this point, and eagerly await further enlightenment from you. DrD
  14. By tradition / convention, watches and clocks use cycloidal gear teeth. These produce a constant velocity ratio and a fixed pitch point, just as with the much more common involute gears. However, the center-to-center distance is very critical for correct action with cycloidal teeth, in contrast to the considerable flexibility offered by involute gears.
  15. When I have interviewed candidates, I have been known to sketch a problem on my blackboard and ask them to set up the describing differential equation and solve it. (They usually get the shakes and collapse at this point!) I have also asked if the candidate is familiar with particular textbooks that I considered important for work in the area at hand. I have asked if they know how to code is various computer languages, depending on what was in use at the time and place. I have asked why the candidate wishes to work for this particular employer. They usually don't know, or at least cannot express it.
  16. FEA stands for Finite Element Analysis. The FEA approach breaks a domain into many small (but not infinitesimal) subdomains or elements, and then attempts to satisfy the describing equations within each element. The result is a very large number of usually linear equations to be solved simultaneously to obtain the describing values in each element. There are many good books and countless papers on this subject. Go find some of them and read more to obtain a greater understanding. DrD
  17. Look at the construction of a small IC engine, such as for a motorcycle. That has all the construction features you need, but be aware that hydraulic oil is only slightly compressible. If you ever try to move the piston to compress the oil, the valves must be open to allow oil to flow out; otherwise, you will bend the connecting rod and/or crank. DrD
  18. The sonic boom in air is a compressibility effect. Water is almost incompressible, therefore, I would not anticipate any boom in water. DrD
  19. Industrial safety does not have a whole lot to do with the mass moment of inertia. Industrial safety is largely common sense. If you don't understand what is going on in an area, stay out of it. If there is the possibility that there may be something moving so fast you cannot see it, stay away. If there is the possibility of something falling on you, don't go under it. If there is the possibility of you falling, use a safety belt, a safety line, or stay out. Always wear your hard hat and watch for overhead obstructions (like pipes, machine parts, etc) and holes in the floor. (My hard hat from my steel mill days if covered in black marks where I ran into things while I was looking at the floor to avoid pitfalls.) Stay out of high noise areas. If you must, wear hearing protection and limit your exposure time. (I'm deaf because I worked too long one high powered sonar transducers.) Wear safety glasses wherever indicated. They are a pain in the neck, but they sure beat being blind! Wear gloves, aprons, steel toed shoes, etc as indicated for the situation you are going into. That's about it. DrD
  20. Just what does M.S. pipes refer to? I read this as "Main Steam pipes," but perhaps you had something else in mind. It would be really nice if that actual question had a direct relation to headline. DrD Just what does M.S. pipes refer to? I read this as "Main Steam pipes," but perhaps you had something else in mind. It would be really nice if that actual question had a direct relation to headline. DrD
  21. Off hand, I cannot see any reason why this would not be possible, provided you had sufficient power available. More to the point, why would you want to do this? What is the point? In what circumstance can you see this being useful? DrD
  22. And the design of a gantry crane has what to do with bolts in bending? It would be a real benefit to other readers for the title and the question to have some obvious connection!! DrD
  23. Have any of you ever worked on an actual IC engine? This is absurd!! Such an engine would produce power only once in 3 crank revolutions. It would require a huge flywheel simply to keep it moving during the remainder of the time. If this was a viable idea, why do you think it is not already in production? Someone would have already done it, except that it does not work well at all. DrD
  24. Much of the answer depends on whether your system is static or dynamic. If it is static, alpha is zero, so that I*alpha is also zero. For a static system, you usually do not need to know I. If your system is dynamic, then you will need a value for I in many situations. DrD
  25. I think you are asking what is the use for the mass moment of inertia (MMOI) in mechanical design. Any time you want to apply the rotational form of Newton's Second Law, T = I * alpha, you will need the MMOI calculation to provide the value for I. If you are asking specifically about the expression for a solid, homogeneous sphere, the I might suggest that you consider writing the T = I * alpha relation for a ball, such as a single ball in a ball bearing. DrD