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Radial displacement mechanism

  1. Apr 13, 2016 #1
    This is a hard one to describe and I couldnt think of a better tittle, sorry.

    My aim has been for a while to create a mechanism which allows me to move an object (i.e a washer or something) in or out radially along a spoke of a wheel. However I have some restrictions which have made me scrap my designs so far (most of them involved very complicated mechanisms with lots of moving parts) so I've decided to look for some help.

    The mechanism needs to be able to be controlled from off of the axle (it cant be rotating with the spokes, that creates an issue of how you access or actuate the mechanism itself when its spinning with the axle). See the video below for an example.

    The design in the video uses a disc with spiral groves which is rotated relative to the axle and that forces the bolts to slide radially outwards. This presents the issue of how do you isolate the movement of the spiral disc from the rotation of the axle?

    I've seen designs like this
    which use a scissor jack like design. The issue this presents though is that the device takes up a lot of space width wise.

    The washer/object that slides along the spoke must be able to be held in place by the mechanism to stop it from sliding up or down the spoke to a new position.

    Anyone have any ideas?

  2. jcsd
  3. Apr 18, 2016 #2
    Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
  4. Apr 18, 2016 #3


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    A differential can solve this issue. A relative change in position between an inner shaft and a sleeve would actuate the motion desired. The differential would hold the relative speed between the inner shaft and outer sleeve at zero. You would move the last part of the differential to vary the relative position of the inner shaft and outer sleeve. Make sense?
  5. Apr 18, 2016 #4


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    We need more information:
    1.Is there just one washer, or many on one, or on many spokes?
    2.The technique used to hold the washer to the spoke will depend on the maximum RPM, and what it is doing there. What does it do on the spoke?
    3.Are your spokes round wires like most bicycle spokes, or plastic or cast alloy?

    I would consider an internally sprung unit that self locks to the spoke. Pressing either side unlocks it and permits it to move along the spoke. A fixed diagonal arm with adjustable radial position can then sweep a washer to the radius required. A “Gripple” or “Fastlink Wire Joiner” has two internal spring loaded clutches or wedges. https://en.wikipedia.org/wiki/Gripple

    If the spoke was threaded, the washer could be a nut. Friction to the nut on one side of the wheel will move it outwards, on the other it would move it inwards.
  6. Apr 20, 2016 #5
    My first though was a swash plate, similar to a helicopter rotor. But with the push/pull rods at an angle out radially or another pivot point changing the direction of motion outward.
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