6
$\begingroup$

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.

enter image description here enter image description here enter image description here enter image description here

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

enter image description here

$\endgroup$
5
  • 3
    $\begingroup$ 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. $\endgroup$
    – wwarriner
    Nov 16 '15 at 2:49
  • $\begingroup$ @starrise Thanks. Are you referring exclusively to the inner corners or square design in general. $\endgroup$
    – skibulk
    Nov 16 '15 at 2:52
  • 2
    $\begingroup$ 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. $\endgroup$
    – Fred
    Nov 16 '15 at 3:16
  • $\begingroup$ @Fred Is there a rule of thumb for how much they should be rounded? $\endgroup$
    – skibulk
    Nov 16 '15 at 18:11
  • $\begingroup$ 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. $\endgroup$
    – Fred
    Nov 17 '15 at 1:06
4
$\begingroup$

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

enter image description here

$\endgroup$
1
  • 1
    $\begingroup$ So many moving pieces! I'd like to find something simpler, but I'll consider this. $\endgroup$
    – skibulk
    Nov 16 '15 at 2:55
4
$\begingroup$

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.

enter image description here

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

$\endgroup$
1
$\begingroup$

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.

enter image description here

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.