4-bar linkages: drag and play
- Find a set of lengths for the bars AB, BC, AD and CD such that the point E is moving on a straight line (not necessarily on its full movement, just partially). This is not possible.
- Learn the order of the appearing curves. They are sextics.
- Construct Chebyshev's linkage (1854) by choosing suitable lengths for the bars. AB=4, BC=AD=5, CD=2.
- Construct Watt's linkage by putting B=(7,-2) and choosing BC=AD=4 and CD=2.
Sánchez's trick
It is a bit tricky to disallow moving D over the possible domain. Here is how you can achieve that in GeoGebra:
- Define a variable to store the path parameter for D in a variable, by entering say
ppd=PathParameter[D]. - Type
i=1. - Make sure that point C is defined as
C=Intersect[c,e,i]. - You need to edit the Scripting/On Update setting for the point D by using the following piece of code:
if (ggbApplet.getValue("x(E)")) {
var ppD = ggbApplet.getValue("ppD");
ggbApplet.evalCommand("ppDok="+ppD);
} else {
var ppDok = ggbApplet.getValue("ppDok");
ggbApplet.evalCommand("SelectObjects[]");
ggbApplet.evalCommand("SetValue[D,Point[d,"+ppDok+"]]");
ggbApplet.evalCommand("SetValue[i,3-i]");
}