Pros and Cons of jackshaft power.

Discussion in 'Metal Boat Building' started by Capt Sport, Apr 8, 2007.

  1. alan white
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    alan white Senior Member

    Hope that last comment was helpful. My mechanical explanations are not very technical, not knowing the engineering terminology I should be using.

    A.
     
  2. BillyDoc
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    BillyDoc Senior Member

    Good morning Alan,

    Well, you may be right about the "fun" thing, I found myself looking forward to getting to the office to continue this discussion! Weird, I know.

    I think I'm beginning to get it here, but I'm not at all sure! I understand about the prop shaft (or jack shaft, or drive shaft) issue with two "U" joints in it. The driving shaft has a constant rotational speed, the shaft between the two "U" joints speeds and slows every revolution if there is a displacement of the input and output axes, and the output shaft is again constant as the final "U" cancels the effect of the first. Your "V" drive mechanism seems to me to be a horse of a different color, though. Namely, because the output of the mechanism does not travel through the "U" joint at all. The "U" joint's only function that I can see is to constrain the "pie" in rotation about it's long axis.

    But if I understand you correctly, this long axis constraint is not quite perfect, just like in the prop shaft example above, but instead of a rotational velocity variation like with the prop shaft there is a "path" variation at the second crank, i.e., the path described is not quite circular! Which would lock the whole mechanism up, of course.

    Now it seems to me that the problem can be cured by substituting a CV type of joint for the "U" joint you show. Is this correct?

    BillyDoc
     
  3. alan white
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    alan white Senior Member

    The funny thing is, I never took a CV joint apart. I could intuit (given some time) how to make one, but the term "constant velocity" means, to me, friction because i am guessing there are sliding surfaces within to accomplish the same pitchline velocity.
    It is simple to add the mini-cranks (eccentrics) on the two fixed bearings of the U joint and manitain the original design as shown which has high efficiency compared to other V drives. I haven't contemplated the pie arm being supplied with a bearing allowing the arm to tilt, but that's even simpler.
    Here is how I look at drive design: There is no use in simply getting the job done because I can come up with ten ways to replace gears if the ratio is limited to 1:1, but all ten have friction contact, and if one can stay with rolling contact, then it's worth putting an effort into a design.
    You should see my wobble plate reduction drive, which works on the same principles. It transfers a lot of power at maybe 98-99% efficiency.
    Also, differentials can be built with trochoidal races.
    The importance of high efficiency is underrated. A sailboat winch, for example, can waste 15 % of the operator's power, which means the winch handler in a race situation must be 15% stronger to do the same work.
    Another example is the shaft-driven Harken pedestal winch crank that two men operate. Three gearboxes are used minimum, meaning a loss of the power of nearly one whole man! I improved that system on paper, using my own right angle bearing drive, calculating about a 4%-6% loss.
    I also designed a 5 speed winch with only three moving parts that was at least 98% efficient.
    The use of gears is a matter more related to interchangability of jobbers and gear sets, and close ratios like 1.1:1 (11 teeth, and 10 teeth). those ratios are hard to get with roller drives (but not impossible).
    I also like roller drives because almost nobody understands them, leaving the door wide open for experimentation. If you played around with them, you'd get hooked, Billy. Even knowing you probably will never do anything with a design, it's cool to know you are actually creating something new in your head. Something that's never existed before that is better.
    I gave up on the idea of patenting years ago. I realized that I just love to think like a dancer likes to dance. I can, for instance, spend a long roadtrip alone and arrive hours later with a whole new mechanism done.

    Alan
     
  4. SamSam
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    SamSam Senior Member

    I got this from Google, apparently there's more than 1 kind...''1. v-drive The V shaped part of a women's body below the waist.At bikini or wet tee shirt contest: Look at that v-drive on contestant seven. I think the number nine has the best v-drive.''
     
  5. alan white
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    alan white Senior Member

    Talk about Jack shafts invariably shifts to V-drives, usually at about age 12.
    The V-drive simply offers more positions to run the shaft. It's not as efficient, of course, as using a jack shaft. It costs more to install it, and maintenence is higher.
    After it's been installed, the rear end usually is quite a bit heavier. It's unavoidable, and a lot of sailors go back to the simple reliable jack shaft eventually.

    A.
     
  6. alan white
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    alan white Senior Member

    This is the L drive.
     
  7. alan white
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    alan white Senior Member

    The L drive would serve as a variable angle drive, so that the angle could be adjusted easily. It's shown with two outputs, but a single output (the top shaft) would link with another L drive next to it which would swing on the (as drawn) vertical axis. Two internal bearings are used. The little picture on the side is a winch crank station showing three of these boxes, the last one under a winch.
    Again, cranks are used. The upper shaft is pressed around the lower one and a ring on needle bearings between them has a pin onto which the horizontal shaft is attached via a needle bearing (upper right corner).
    This setup has almost no friction, as would a U joint.
    It should handle a huge torque load in a very compact case. It is not much more complicated than a universal joint.
    I've never seen such a drive anywhere, and I don't know why not. It's simple and reliable, has no backlash, and uses almost no energy. It replaces a set of bevel gears, which make noise and will not last as long, nor run as efficiently.
    Many people don't realize that worn gears can set up vibrations that wear bearings (which wear gears more, etc., ad infinitum).

    Alan
     
  8. BillyDoc
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    BillyDoc Senior Member

    Alan, you will love the CV joint. Go here to look at a drawing: http://en.wikipedia.org/wiki/Constant-velocity_joint. There are no sliding surfaces, only rolling. In fact, it functionally resembles a bunch of ball-bearing sections with deep grooves to take axial loads. I think using one in your design would make one hell of a good "V" drive!

    And I see how the "L" drive inspired you, that is also a damn good idea.

    Your comments about driving and designing also touched a chord, I do exactly the same thing. I actually like to take long road trips alone for exactly this reason. Of course, I sometimes arrive somewhere I didn't intend to go . . . but at least (so far) I have arrived intact, albeit in a bit of shock as I realize no one was driving for the last 50 miles or so.

    I fear we hijacked this thread, and I did the same thing on the "Pirate" thread not too long ago (mea culpa everyone, sorry!) but on that thread a little piracy is to be expected. I would, however, hate to see your "V" drive concept get lost, so I wonder if there is any way to clip out this part of the discussion and move it over to the "propulsion" thread where it belongs. Does anyone know how to do this?

    BillyDoc
     
  9. TerryKing
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    TerryKing On The Water SOON

    HiJackers!

    This is too good a discussion to lose it. Jeff can move a section or a whole thread to another name/forum. If you make a new thread in PROPULSION, um... Hmmm. There are only sub-forums, not a general discussion. INBOARDS (Inboard and Vee-drive hardware) is OK if you think this is primarily propulsion-related. Or ask Jeff to make a new sub-forum on "Mechanisms and Drive Systems" or something like that??

    Then this part of the discussion can be moved there...

    I want to start a thread on using modern integrated transverse auto/truck engine/drive systems, but that fits pretty well in "DIY Marinising".

    Maybe there should be a "General Discussion" section in PROPULSION where tradeoffs and decision-making and stuff like this could go???

    What do you guys think??
     
  10. alan white
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    alan white Senior Member

    The discussion began with a drive component. I leave it up to others to decide if the thread should be moved. I vote for a thread entitled "investigating devices and mechanisms".
    Thanks for the word on the CV joint. I would have assumed balls in semi-circular curved grooves (I haven't yet gone to that link). The contact is rolling, yes, but not without sliding surfaces. If you don't agree, make a gutter out of sandpaper and roll a billiard ball down it. See how the sides of the ball scuff, but not the middle. They are efficient, but in theory no part of them actually rolls! You could say ONE line on the balls rolls, but it is really a nonexistent line on a perfect sphere. Finding it is like finding the last distance to the wall that can't any longer be divided by two.
    I'm glad to have some comrades here who enjoy the challenges of geometric thought. I find it very rewarding. If anyone remembers the German airplane designer from "Flight of the Phoenix", they might guess that character was the one I relaed to.

    Alan
     
  11. TerryKing
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    TerryKing On The Water SOON

    Great Movie!!

    Alan, you mean you only make MODEL boats?????? We're depending on you to float US!!
     
  12. alan white
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    alan white Senior Member

    Having gone to the CV link, I see it is as imagined. I invented a similar mechanism when I was nineteen. My next door neighbor had a friend who was a retired GE turbine designer. My neighbor sent him the drawing and wrote back a short note telling me the mechanism would lock up.
    I was a bit miffed! I got his number and called him. It took about ten minutes to explain to him why it wouldn't lock up, and he was pretty embarrassed.
    So much for engineers with phds.
    My device was a 90 degree drive, any ratio. A wheel with ball bearings contacted (dipped into) a wheel (as if one took a cartridge off a turntable tone arm and replaced it with a wheel that rolled. Like a turntable, the ball wheel axis was offset (also like a differential hypoid gearset). The semi-circular grooves on the "platter" wheel were shaped like the letter S, starting towards the center and ending near the rim.
    Soon after, I showed the design to a Ratheon engineer (who was also the owner of a 42 ft Alden cutter), an old friend of my fathers with whom I had more in common with than my father ever did).
    He was quite astute in mechanical stuff. He was the one who pointed out the scuffing problem with balls in grooves. Aha, I said.

    Alan
     
  13. alan white
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    alan white Senior Member

    Es macht nichts. Aber ich brauche doppel freuleinen so mein kopf kann klaar sein. Verstehen?

    Alan
     
  14. BillyDoc
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    BillyDoc Senior Member

    Yup! Verstehen gut! Got Bable Fish!

    "It does not make anything. But I need double being pleased linen so my head can klaar be. Understand?"

    But on a completely different topic, I think the grooves on the (C)V joint can be designed so that there is no more scuffing than in any other ball type mechanism. I agree that needle-type bearings are far better though! And they fit in tighter enclosures as well. I reference your post #50, above.

    BillyDoc
     

  15. TerryKing
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    TerryKing On The Water SOON

    Flying and Floating Models

    Nicht nur kenne Ich nicht die antwort, aber verstehe Ich nicht die frage!

    (And I thought I forgot all that high school Deutsch)...

    It seems your head can see mechanisms very clearly... but I really have trouble visualizing some of your ideas. Maybe you can get to drawing in some CAD or Visio thing.. (I could mail you Visio if you want...)
     
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