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Thread: leverage angles?

  1. #11
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    As there perhaps seems to be a little confusion understanding my drawings i've added 2 more. These are just 2D plans, viewed from directly overhead.
    Pic 1 shows the wheel axle offset to put it perpendicular to the central shaft of the muller, and pic 2 shows the pivot point for the arm offset so as to bring the axle to a perpendicular from the central shaft.
    My original question was whether anyone thought either design would change the downforce from the muller wheel, however a few posts here have led me to put some more thought into this.
    Roller 1.png Roller 2.png
    Quote Originally Posted by kcoffield View Post
    ......However, the position of the pivot and arm geometry can/will affect if the wheel stays tangent to the arc throughout various sand depth and as it travels through its range of motion. ......Kelly
    The pivoting arm is just for allowing the wheel to move up and down as it passes over "lumps&bumps". Whilst its range of motion appears large, in use it should only go up and down a small amount, thus keeping the axle close to perpendicular to the circle of rotation.

    Quote Originally Posted by mpowley66 View Post
    Personally I don't like the first design because I think it will cause a greater moment at the pin joint between the fixed and the pivoting arm. I would favour a design like others here have done where the arm that attaches to the wheel pivots like a control arm on a car.
    Both designs are trying to allow the arm to pivot up and down. Can you elaborate a bit more on what you mean by the "greater moment at the pin joint"?

    Quote Originally Posted by Petee716 View Post
    .......Does the torque you're trying to change pertain to the sizing of the power source, or the wheels interaction with the sand? Maybe this will help, maybe it won't............The wheel is set at 90 degrees to the drum rotation and the axle is parallel to the floor of the drum. The scrubbing action under the wheel that Kelly describes above is what I'm looking for. That's really where the desired action is. Just the basic physics of the motion of the thing will always create that scrub (radial motion of the drum plus linear vector of the wheel). I can change how much the wheel "drags arse" a little bit by its position on the mounting bar. The plows just fold and mix the sand. Additionally though, the plows also channel and guide the sand stream to the wheel. This is where things get interesting and a little difficult. Long story short, the wheel stops turning when the contact point gets choked with sand.............
    Pete
    Thanks Pete, I did read your build thread thoroughly. I hope my new drawings portray my design better. I'm not so concerned at the torque to drive it. More so that either one should keep the wheel at 90 degrees to rotation, and the axle parallel to the floor. I am hoping with a longer trailing arm that the wheel should ride up if the contact patch gets choked and prevent the wheel from stalling.

    Quote Originally Posted by r4z0r7o3 View Post
    .........The longer the axle, the more opportunity for it to flex in the direction you don't want. One idea to mitigate that, and a related topic: Has anybody ever experimented with a hinged axle? i.e. so the wheel can hinge "up" and ride over bumps in the sand...relying on it's weight to smoush, rather than a rigid axle.
    In my crappy renderings I may have given the impression that the pivot point for the trailing arm and the wheel axle are a bit lengthy. But they wont be as long as they appear. I just drew them that way so the points of interest were more obvious. Sorry 'bout that.

    Cheers Phil
    So, whats your Plan B?

  2. #12
    if you draw a line from the center of the wheel to the center of the muller shaft, this will form a triangle with the pivot arm and the muller offset arm, the height of the triangle in feet times the weight of the wheel in lbs will give you the delivered ft/lbs of torque to the wheel. the angles between the arms won't make any difference whether they are at the wheel or at the offset arm, the longer the pivot distance the more torque delivered.

    Art b

  3. #13
    Senior Member r4z0r7o3's Avatar
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    Quote Originally Posted by 12bolts View Post
    But they wont be as long as they appear. I just drew them that way so the points of interest were more obvious.
    ...my bad too, I shoulda said wheel-arm instead of axle. Meaning the entire structure between center-pivot and wheel.

    Quote Originally Posted by master53yoda View Post
    if you draw a line from the center of the wheel to the center of the muller shaft, this will form a triangle with the pivot arm and the muller offset arm, the height of the triangle in feet times the weight of the wheel in lbs will give you the delivered ft/lbs of torque to the wheel. the angles between the arms won't make any difference whether they are at the wheel or at the offset arm, the longer the pivot distance the more torque delivered.
    Aye, yoda's right, and also remember in reality, this isn't a perfectly rigid structure, steel flexes. The more the steel between the center pivot and the wheel, the more opportunity for flex. Keep it short, keep it simple. That's why I asked about just using a hinge, it would allow for a straight arm. If you're worried about a hinge tilting the wheel, make a trapezoidal joint. So, viewed from the side:

    Code:
    (ASCII-CAD - not to scale)
    
                          ##
      |                   ## |
      |             o--o  ## |
      |          []-|  |==## |
      |          [] o--o  ## |
      |          []       ## |
      |          []       ## |
      \----------[]----------/
    
    Key:
    
    [] - center column
     | - steel
     - - steel
     o - joint
     = - wheel axle
     # - wheel
    Besides being more complicated, the other down-side is the joints will allow more front/back slop in wheel position. That's why I like the simple hinge idea better. It's three fewer joints to worry about getting sand inside.
    "Things that are complex are not useful, things that are useful are simple."
    - Mikhail Kalashnikov

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