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Guidance needed in prototype development

  1. Sep 5, 2014 #1


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    Hello. First off I would like to apologize if my questions are common sense, I have done my own research with some progress but with some stopping points that I hope to get pushed in the right direction here. I am trying to build a system that is similar to a bike with a free wheel so it can spin freely in one direction and engage in the other. The issue I am having is finding a way to change how much load is required to rotate the system without switching to different size gears to change ratios. When searching online, I found the Nuvinci continuously variable planetary drive which is what I think I would need to accomplish this. But I do no know if there is something better. There will be no motor to this system, it will use gravity as its drive. I will eventually want to be able to set the "weight" digitally or some other way that can allow for easy changes in the required weight to rotate the system, but my main priority is knowing what to look for. The minimum weight that I am trying to accomplish is 50 pounds, and the maximum 300. I understand that that may be a large gap so I realize the gap may need to be reduced, and if so I would raise the minimum rather than reducing the max. If any can help or tell me whether I am even searching in the right place here than I would greatly appreciate it. If anything is unclear or any more details are needed, please feel free to ask. Thanks you!
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  3. Sep 7, 2014 #2


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    It's difficult to help you decide if the Nuvinci is acceptable for your application without know what it is, but a continuously variable transmission will give you excellent flexibility in terms of gear ratio.

    When you say "there will be no motor to this system, it will use gravity as its drive," are you hoping to develop a continuously-spinning mechanism of some kind that runs on gravity alone?
  4. Sep 8, 2014 #3


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    I think when I said gravity it came out wrong. I mean gravity as the gear system will rotate by a handle that is attached that when a certain load is put on the handle, it will pull down and rotate the chain depending if the drive is set to that weight or less. It will not be a continuously spinning mechanism, it will be a stop and go system that will test different weights for rotating the gear and chain. Thank you for responding, hope I made it a bit more clear.
  5. Sep 9, 2014 #4
    A pair of spur gears, axis of rotation offset (offcenter) equally in both cases,pcd engagement adjusted automatically by a cam & finger arrangement will allow for a high starting torque changing to a high rpm after 180 degrees of rotation.This, hopefully, may act as a stop & go system.
    I can try & make a rough sketch.
  6. Sep 9, 2014 #5


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    Thank you, that would be great! I appreciate it very much, I have everything pictured in my mind as well as rough sketches. Unfortunately I lack the knowledge as of now of what can give me my desired outcome. So any help to get me moving in the right direction will make the world of difference. This is only a step in the door as I have other systems I will pursue building as I complete this one.
  7. Sep 10, 2014 #6
    The attached assembly drawing indicates a cyclic,continuously variable input/output speed/torque for every 180 degrees of rotation.

    Attached Files:

  8. Sep 10, 2014 #7


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    Thank you, that helps a lot in giving me some ground to use to develop my system
  9. Sep 15, 2014 #8
    soo...I'm too stupid to understand from a drawing what that thing is? Is there a gif or something that would let me visualize it better?

    btw, internally geared hubs like the one you suggested are efficient when they're in the direct drive (1:1 gear ratio; or really, no gears), but they start to lose mechanical efficiency as you start shifting, and by the time you get to the highest/lowest, you're at 91%. I don't know how much you care about that, but it's a big deal for cyclists.

    rohloff hubs are different though. they're basically small transmissions, but for bicycles. and super expensive.
  10. Sep 16, 2014 #9
    Both gears are identical, with an off centered axis of rotation.At the max. torque position, the smallest radius of the input driver meets the largest radius of the output driven gear.When the diameters are rotated 180 degrees, the largest radius of the input gear engages the smallest radius of the driven gear.High torque, low speed at start to low torque, high speed after 180 degrees.A cam will maintain the varying gear distances.
    I had prototyped a cycle rickshaw where 360 degree rotation pedals were replaced by semi rotating treadles.These treadles were longer for better leverage.I hope to try out the gear assembly in my next proto.
  11. Sep 17, 2014 #10
    If this gear assembly is coupled to the output shaft of a single cylinder IC engine, would it influence the output characteristics of the engine?
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