1:17
Crank-rocker
Four-bar linkage series, part 1: one crank turns fully while the rocker swings. The Grashof condition tells you when this is the case.
Four-bar linkage series · Part 2 · ASOMmini
The double-crank
Both links pivoted on the frame turn fully – two cranks. This works when the shortest link is itself the frame.
1:22
The principle
The shortest link as the frame
The double-crank also meets the Grashof condition: the shortest and longest links together are no longer than the other two. The shortest link a then turns fully relative to its neighbors b and d.
If a is chosen as the frame, both neighbors become cranks. The coupler c makes one full turn relative to the frame but only swings relative to b and d. Double-cranks are found, for example, in production and agricultural machinery.
What the video shows
- Link lengths a = 76 (shortest link), b = 191, c = 124 and d = 219 (longest link).
- The Grashof condition is met: a + d = 295 is less than b + c = 315.
- a is the frame. The trajectories show it: b and d both turn on full circles.
In ASOMmini
From the textbook straight into the model
In ASOMmini, you build every type in this series with just a few clicks and immediately see how it moves.
Change lengths, see the effect
Move a joint, and ASOMmini recalculates the motion in real time – so you can see when a link no longer turns fully.
Paths and diagrams
Trajectories show the paths of the joints, and diagrams show angles, velocities and accelerations over the entire motion sequence. More on analysis
Forces and torques as well
With masses, springs and friction, the basic type becomes a concept whose forces and torques you know. More on force calculation
Four-bar linkage series
All example videos
More parts of the series
1:17
1:21
Double-rocker
Four-bar linkage series, part 3: if the frame is opposite the shortest link, both rockers swing and only the coupler turns fully.
1:01
Parallelogram and antiparallelogram linkage
Four-bar linkage series, part 4: links of equal length are opposite each other, as a parallelogram or crossed – the limit case of the Grashof condition.
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