Linkages beat gears for short movements
Where a linkage is simpler, cheaper and more reliable.
A linkage beats a gear train for a short, limited movement because gears earn their keep specifically at continuous rotation, meshing tooth after tooth across many full turns, while a mechanism that only ever needs to swing a lever back and forth through a modest arc gets none of that benefit and pays every one of a gear train's costs, extra parts, backlash, and the ongoing need for lubrication, for a job a few rigid bars could have done just as well.
Why gears are not always the right answer
A gear train is built to solve a specific problem well, transmitting continuous rotary motion between two shafts at a controlled, repeatable speed ratio, and its whole design, precisely cut teeth meshing in sequence, exists to keep that transmission smooth and accurate turn after turn indefinitely. A mechanism that only ever needs to move something from one position to another and back, a lever tripped occasionally, a latch thrown a few times a day, has no continuous rotation to transmit in the first place, which means it gains nothing from a gear train's actual strength while still inheriting its costs, tooth wear, the need for lubrication, and backlash that has to be managed even in a mechanism that barely moves.
This mismatch is easy to fall into precisely because gears carry a reputation for being the serious, capable answer to any motion problem, and reaching for that reputation without checking whether the actual motion needed matches what gears are good at is a habit worth resisting. A short, occasional movement is a fundamentally different engineering problem from a continuous, high-cycle rotation, and the two deserve genuinely different default solutions rather than the same one applied out of familiarity.
The light-switch comparison
An ordinary wall light switch only ever has to move its internal lever through a small arc, a few tens of degrees, to make or break an electrical contact, and nobody builds that switch around a gear train, because a simple toggle linkage does the entire job with two or three rigid parts and a single pivot, needing no lubrication and having no teeth to wear down over years of occasional flicking. A mechanical clock's hour hand, by contrast, genuinely needs continuous rotation locked to an exact fixed ratio against the minute hand turning twelve times faster, a job gears are specifically built for and a linkage has no sensible way of doing at all, since nothing about a simple pivoting bar can encode a repeating twelve-to-one ratio the way a pair of meshing gears does effortlessly. Neither mechanism is the generally better one, each is simply matched to the specific kind of motion its own device actually needs.
Why fewer parts means fewer ways to fail
A linkage doing a short movement typically needs only a handful of rigid links and pivots, each pivot a simple, largely maintenance-free joint, while an equivalent gear-based mechanism needs precisely cut teeth meshing correctly, a housing to keep contamination away from those teeth, and periodic lubrication to keep wear manageable over the mechanism's life. Every one of those additional requirements is a place a gear-based solution can fail that a linkage-based one simply does not have, dirt fouling the mesh, lubricant drying out or migrating away, a tooth chipping under an unexpected shock load, none of which have any equivalent risk in a mechanism built from plain rotating pivots doing nothing more complicated than swinging through their own arc.
The number that matters here
A short-travel linkage mechanism built from two or three links commonly needs a small fraction of the individual parts a gear train achieving the same limited motion would require, and correspondingly needs no scheduled lubrication at all across a service life where an equivalent gear mechanism would need periodic attention simply to keep its teeth from wearing prematurely. That gap in part count and maintenance need is the entire case for a linkage over a gear train whenever the actual motion required genuinely is short and limited rather than continuous, and it is worth stating plainly because that case rarely needs any calculation at all to make, simply an honest look at how the mechanism will actually spend its working life.
What this changes in practice
Choosing between a linkage and a gear train starts with asking honestly whether the mechanism actually needs continuous rotation at a fixed ratio, or merely needs to move between a small number of positions, since only the first of those two needs is what a gear train was actually built to solve well. A designer who reaches for gears out of habit, or because a geared mechanism looks more sophisticated on a drawing, on a job that only ever needed a simple pivoting link, has paid for complexity, maintenance and failure modes the actual motion never required in the first place. Sketching the actual motion a mechanism needs before choosing how to produce it, the same habit covered for cams earlier in this set, tends to surface which of the two the job genuinely calls for well before any detailed design work begins.
Where this stops being true
A short movement that also needs to carry a genuinely large load, or needs an unusually precise, repeatable position at each end of its short travel, can still favour gears or a geared reduction over a simple linkage, since gears offer a controllable, calculable mechanical advantage and positioning accuracy that a bare linkage's geometry does not automatically guarantee on its own. Short travel alone is not the whole test, it is one factor among several, and a mechanism carrying real load or needing fine positional accuracy may still need the very complexity a purely short, light-duty movement would have been better off avoiding. The honest question is always what the specific movement needs, continuous rotation, heavy load, fine accuracy, or none of those, rather than defaulting to either mechanism purely out of habit.