Instructions:
Click and drag on the canvas to interact.
- Clicking further right from the centre makes the yellow bar longer.
- Clicking further left from the centre makes the yellow bar longer but in the opposite direction.
- Clicking further up from the centre makes the last bars longer.
- Clicking further down from the centre makes the last bars longer but in the opposite direction.
The coloured lines in the middle (so all except the dark blue line) constitute the bars of two related 4-bar linkages.
- The first 4-bar linkage consists of bars coloured green, yellow, cyan and red.
- The second 4-bar linkage consists of bars coloured green, yellow, magenta and white.
The green bar is of constant position and length which acts as the stationary object to which the mechanism is fixed.
The yellow bar is driving the mechanism. The angle it makes with the green bar is increasing at a constant rate.
The remaining bars are in two pairs:
- The first pair is (cyan, red) and the second pair is (magenta, white).
- Each pair is one of the two solutions to the problem of where the two remaining bars (of given lengths) must be in order
to complete the 4-bar linkage (such that the last bar connects to the other end of the green bar.
This reduces to the problem of finding a triangle with two fixed length sides where the remaining side must have adjacent vertices
at given positions and any such solution may be mirrored about that remaining side and still be a solution, we in general have two
solutions and hence the two 4-bar linkages.
The green dots graph out the two solutions for angle that the last bar makes with the green bar (y-axis with top and bottom of screen
being the bar pointing left from its pivot with the green bar) over the angle that the yellow bar makes with the green bar (x-axis where
left and right of screen being a yellow bar pointing right from its pivot with the green bar).
- The blue vertical line represents the current angle that the yellow bar makes with the green bar.