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I want to convert rotary motion (the orange propeller) onto a square path (the dark gray path). Is this a valid way to go about it? Would it be possible to use a square peg instead of a round one (the red circle) in order to keep the peg level as it travels? If not how could I keep it level? I'm a noob.

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Update 2015/11/16 - Posted another option as an answer below

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skibulk
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    From a materials standpoint: corners are stress concentrators and could wear down rapidly. May consider using slightly rounded corners on the inside of the track. – do-the-thing-please Nov 16 '15 at 02:49
  • @starrise Thanks. Are you referring exclusively to the inner corners or square design in general. – skibulk Nov 16 '15 at 02:52
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    To reduce wear and stress in the corners & to have a smoother travel for the red peg, the path followed by the red peg should form part of a circle in the corners. Both sides of the channel the red peg is in should be curved at the corners. – Fred Nov 16 '15 at 03:16
  • @Fred Is there a rule of thumb for how much they should be rounded? – skibulk Nov 16 '15 at 18:11
  • The width of the channel followed by the red peg needs to be uniform throughout. This is easily done on the straights; a bit more difficult to do on the corners. Ensure the curvature on the inside and outside of the channel produces a uniform thickness; the same as on the straights. As to the size of the curvature, it comes down to what you want to achieve: too much curvature will produce a quasi circle - not what you want, too little curvature & you end up with high resistance to movement at the corners. – Fred Nov 17 '15 at 01:06

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There is an existing method using a reuleaux triangle. It was used for moving film in a stepwise motion in projectors.

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ratchet freak
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If you're going with square peg and don't strictly restrict its rotation (e.g. with mechanism like in Ratchet freak's answer), you WILL run into problems with technical tolerances - it will be catching on the corners and with any other shape than round you will have this problem.

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Your original image mechanism can work okay, but modifying the peg to be square will break it.

SF.
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The reuleaux triangle is a great solution but I would prefer something that has fewer parts and is more compact...

Here's another option. The idea is to sandwich a bent peg between offset tracks. So the sandwich goes like this: Bottom Track, peg, Propeller, Top Track (Transparent). And Yes, I would round out the track corners more than depicted.

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skibulk
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