I want a simple mechanism to rotate something 180 degrees when another thing moves linearly past/through it. The below is what I have, but it can only work with an offset, so the movement is never fully 180 degrees. No gears/belts etc., it must be a simple mechanism. Any ideas? 
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1 - 1$\begingroup$ Rack and pinion - easily controllable but you don’t want a gear… $\endgroup$Solar Mike– Solar Mike ♦2023-01-03 15:38:31 +00:00Commented Jan 3, 2023 at 15:38
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2 Answers
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1 You need two slots in 90 degrees angle on each other for the wheel
- 1$\begingroup$ Actually this does give 180 deg motion by doubling the idea i put above - suppose its basically a v simple rack and pinion like @solar Mike said. Bit more detailed diagram would help this be more useful i think. $\endgroup$Oliver Walters– Oliver Walters2024-01-07 11:21:48 +00:00Commented Jan 7, 2024 at 11:21
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6 Without any furter information, the Scotch Yoke is probably what you are after
- 1$\begingroup$ That conversts rotary into linear - the opposite of what the OP requires. As show in your image a push from the right will be stuck on top-dead-centre. $\endgroup$Transistor– Transistor2023-01-03 23:36:25 +00:00Commented Jan 3, 2023 at 23:36
- $\begingroup$ @Transistor It can be used for both cases. Given the constraints that the OP provided I think it a simple and adequate solution. And although you are right there is a dead point, its and unstable equilibrium so even a small force it will move either way. $\endgroup$NMech– NMech2023-01-04 13:49:07 +00:00Commented Jan 4, 2023 at 13:49
- $\begingroup$ Its definitely an improvement on what I put - but yea it still suffers the same issue of there being a dead point, so one can't reliably get the full 180 degrees (though maybe 179.999...) $\endgroup$Oliver Walters– Oliver Walters2023-01-04 16:32:50 +00:00Commented Jan 4, 2023 at 16:32
- $\begingroup$ The other option is the slider crank linkage mechanism ( it still suffers from the same problem and its got more moving components). $\endgroup$NMech– NMech2023-01-04 18:11:08 +00:00Commented Jan 4, 2023 at 18:11
- $\begingroup$ @OliverWalters If you are worried about the dead point, you can use a slight offset between the rotation axis and the sliding axis. You will be sacrificing some degrees (but if radius is adequately large that can easily be under 1 deg. $\endgroup$NMech– NMech2023-01-04 18:14:08 +00:00Commented Jan 4, 2023 at 18:14