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Thread: Debate of the Day: Experimental Chain Tensioner

              
   
   
  1. #11
    Senior Member Stevo's Avatar
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    It looks like his design pivots in the center allowing for chain tightening as the rear suspension compresses. Applying my tensioner's spring load the opposite of the way I have it now, will be a similar effect, I think.
    Current rides: '96 Honda Ohlins VFR, '03 Cannondale C440R, '03 Cannondale Cannibal, '06 Yamaha 450 Wolverine 4x4
    Current builds: WORX.VOR.v3.2

  2. #12
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    Quote Originally Posted by Michael Moore View Post
    With a rear suspension set up like a modern dirt bike (or even many modern street bikes) there is no slack-tight-slack because the axle/pivot/counter shaft are never in line. Instead, the high pivot means the chain is always tightening as it goes from droop to bump. In this case you can often find a point for a stationary roller on the lower run that will take up the slack at full droop and as the suspension compresses and the chain gets tighter the lower run lifts away from the roller. If you can arrange that then you don't need to have a spring-loaded tensioner.

    The ATK system was designed to have an effect on squat characteristics which the spring loaded tensioner won't have. Here's Leitner's patent:

    https://patentimages.storage.googlea.../US4299582.pdf

    cheers,
    Michael
    MMs right. I forgot this is a dirt bike with the always or nearly always downward angled swing arm. Like he says an adjustable but non-articulating(no spring action) idler pully(no teeth) pushing up on the bottom run of the chain would probably be the way to go. I'm thinking you first want to to establish the best drive ratio and then size the sprockets for minimum chain contact with the swing arm slider?
    Last edited by Electro Flyers; 1 Week Ago at 1601.

  3. #13
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    Quote Originally Posted by Electro Flyers View Post
    Because the axis of the drive sprocket is forward of the swing arm pivot axis, the chain tension moves through a slack-tight-slack action as the swing arm moves through its travel. On ICE bikes, normally this action is not excessive because the drive sprocket axis is close to the swing arm. Look at the position of the drive sprocket on this bike. It's much further forward, increasing the slack-tight-slack action and increasing the need for a tensioner.
    Not sure I agree with this - the alignment of the swingarm pivot, drive sprocket and driven sprocket has a bearing certainly; assuming good alignment, for any reasonable measure of suspension travel, the distance from the swingarm pivot to the drive sprocket does not (as long as it's still much smaller than the length of the swingarm itself). Hence, the need for a chain tensioner does not arise as a result of the nature of the mechanism, but rather on account of an angular deviation from 'straight' between the line made by the swingarm under static sag, and line between the swingarm axis and the drive sprocket at the same time.

    As as result, the notion of a tensioner is a tailored solution to deal with a consequence of a given drivetrain layout, and not something that would ever see broader application unless there some very good reason why, in design, the alignment issues couldn't be addessed.

    Eyeballing the alignment in that video, I can see no good reason for the amount of slack present in that chain.

  4. #14
    Senior Member Ted Dillard's Avatar
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    A drawing would be nice...

    (My visual imagination is on the fritz right now lol)
    Power in Flux: The History of Electric Motorcycles
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  5. #15
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    As requested Ted (and in nice Crayola colours too ).

    It all comes down to the ratio of the lengths and the manitude of the Cos scalar. As long as the L1 << L2 then you're never going to be too sensitive to any reasonable deflection.


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  7. #16
    Senior Member Stevo's Avatar
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    That's nice Spoonman!
    Here is my setup (not to scale):
    chaintensioner.jpg

    The stationary "idler" is there to guide the chain between the swingarm pivot and chassis frame crossmember in order to prevent chain wearing on either. There is and needs to be chain slack. As the rear wheel travels up into compression, the chain tightens. That's why when you adjust chain tension for routine maintenance, there must be set slack and your adjustment shouldn't be too tight. Right??!!
    Current rides: '96 Honda Ohlins VFR, '03 Cannondale C440R, '03 Cannondale Cannibal, '06 Yamaha 450 Wolverine 4x4
    Current builds: WORX.VOR.v3.2

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  9. #17
    Senior Member Ted Dillard's Avatar
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    HIS drawing is more better than yours is.




    (well... this IS fight club, RIGHT?)


    yeah, feeling kinda stoopid today, forgive me...
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  10. #18
    Senior Member Stevo's Avatar
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    Who's arguing?!
    I asked for opinions... that could be flaming as well as constructive criticism or suggestions. I really don't know what the optimal way is for me to go with this. I do know that there is a lot of chain slack that needs to be there... I just need to figure out how to deal with it.

    Aww Hell! Maybe I'm overthinking this too much!!
    Last edited by Stevo; 1 Week Ago at 1041.
    Current rides: '96 Honda Ohlins VFR, '03 Cannondale C440R, '03 Cannondale Cannibal, '06 Yamaha 450 Wolverine 4x4
    Current builds: WORX.VOR.v3.2

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  12. #19
    Senior Member Ted Dillard's Avatar
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    LOL

    Well, my first reaction, which isn't at all helpful, is that it sure looks like that chain goes around a lot of corners. Like I said, not helpful...
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  13. #20
    I should be working! furyphoto's Avatar
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    Quote Originally Posted by Spoonman View Post
    As requested Ted (and in nice Crayola colours too ).

    It all comes down to the ratio of the lengths and the manitude of the Cos scalar. As long as the L1 << L2 then you're never going to be too sensitive to any reasonable deflection.

    Chain deflection.jpg
    Can I just say than my understanding of swingarm alignment, and chain deflection just increased about 10000% from seeing this diagram.

    I am in this phase now, I need to add new suspension mounts on my swapped out swingarm, and finalize my motor mount for the drive sprocket position (a tiny bit forward to allow space for future motor upgrade) so this has been on my mind. Now I'm excited to figure out my AUW neutral suspension position, and see if the chain will rub on deflection.

    In your formula, do you have an ball park idea of what actual ratio is represented by "much less than" ( << ) for an averageish motorcycle, before slack becomes excessive?
    -Andrew

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