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I am actuating a small ceramic rotary valve with a cheap mg996 servo motor. The valve has a 90 degree max rotation from fully closed to fully open. Currently I have the servo shaft directly coupled to the valve shaft, and simply limit maximum rotation of the servo to 90 degrees in software.

It would be nice to have the extra resolution afforded by utilizing the servo's full range.

Is there a simple way to reduce the 180 degree rotation to 90 degrees without gears? Space is tight and complexity needs to be minimized.

A push/pull rod on an arm may be the best option, but I'm not aware of other ways to do this.

Note: I have access to a 3d printer.

Thanks!

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    $\begingroup$ pushrod, cam assembly, funky flex-shape assemblies (naturally I can't recall the correct name right now) -- but I rather doubt any of these will be more compact than a ring gear or on-shaft reduction gear. $\endgroup$ – Carl Witthoft Nov 13 '18 at 19:53
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    $\begingroup$ gears are exceptionally reliable and well-understood components. I think the notion that achieving this goal without gear would reduce complexity is flawed - any other mechanism would almost certainly be more complex. $\endgroup$ – Jonathan R Swift Nov 14 '18 at 10:09
  • $\begingroup$ If you are already using software to control the motion, all you need is a end -travel position sensor to feed back a signal so the software will now be close-looped. Now your done. No gears required. $\endgroup$ – William Hird Nov 15 '18 at 23:11
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If space is tight and complexity must be minimized, why not just buy a servo that has 90 degree travel to begin with. There are a number of these available for cheap.

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  • $\begingroup$ This is the most obvious solution... why didn't I think of it? :) After some research, however, I've discovered that 90-degree servos are a bit difficult to find on ebay becuase 1) there don't seem to be that many specifically listed as 90-degree, and 2) many of the most common servos don't list their rotation angle. Still the obvious answer. Thanks! $\endgroup$ – Ryan Griggs Nov 14 '18 at 3:45

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