1:17
Crank-rocker
Four-bar linkage series, part 1: the crank turns fully while the rocker swings. The Grashof condition and the choice of frame tell you when this is the case.
Four-bar linkage series · Part 3 · ASOMmini
The double-rocker
Both links pivoted on the frame only swing back and forth – two rockers. Here, only the coupler turns fully.
1:21
The principle
The frame opposite the shortest link
The Grashof condition is met here as well. The only difference from the crank-rocker and the double-crank is the choice of frame.
The frame is now c, the link opposite the shortest one. Because c cannot turn fully relative to b and d, b and d swing as rockers. The shortest link a becomes the coupler and turns fully relative to its neighbors. If the Grashof condition is not met, no link turns fully, not even the coupler: the linkage is then not rotatable – a non-Grashof or triple-rocker linkage. Whichever link is the frame, both links pivoted on the frame only swing back and forth.
What the video shows
- Link lengths a = 45 (shortest link), b = 160, c = 73 and d = 161 (longest link).
- The Grashof condition is met: a + d = 206 is less than b + c = 233.
- Link c is the frame. The trajectories show this: b and d swing back and forth on circular arcs.
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 – and ASOMmini calculates its forces and torques. More on force calculation
Four-bar linkage series
All example videos
More parts of the series
1:17
1:22
Double-crank
Four-bar linkage series, part 2: if the Grashof condition is met and the shortest link is the frame, both links pivoted on the frame turn fully.
1:01
Parallelogram and antiparallelogram linkages
Four-bar linkage series, part 4: links of equal length are opposite each other, as a parallelogram or crossed – a limit case of the Grashof condition.
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