Position Analysis of a 4 Bar RRRR Grashofian Crank Rocker Mechanism 
Procedure
In this experiment you will guided through the position analysis of a 4 bar RRRR Grashofian Crank Rocker. Like a double crank, in a crank rocker the crank, which in this case is the link 2 does rotate through a full circle. But unlike a double crank, in a crank rocker, the follower, which in this case is the link 4, will NOT rotate through a full circle, and there will be a lower and upper limit for the values of theta 4.
The methods of position analysis of a Crank Rocker are the same as that for a double crank. Using complex numbers is a popular analytical approach. The location of the coupler point can also be determined graphically. An animated description of the analytical as well as graphical methods are provided in the following links.
Unlike the Double Crank, if we try to analytically find out the extrema of the roots of theta 4 by taking derivative of theta 4 with respect to theta 2 and setting the value to zero, it will ultimately be seen that the values are non zero and different, implying that there is a range of values of theta 4. However the simple geometrical consideration that in the extreme configurations, the 4 bar linkage will form a triangle lets us easily find the limits both analytically and graphically. The following animations show the analytical and graphical methods.
Instruments
Choose link lengths, preferably keeping them within 10 units length for easy viewing of animations. Enter them and a coupler arm length and orientation of your choice in the following applet in the designated text boxes. Link 1 represents the ground link. Press the Enter button to verify if your data conforms to a Grashofian Crank Rocker. Note that coupler arm length and orientation play no role in Grashof's criteria, but you are merely asked to enter them for use in later stages. In case you get a message stating that your data does not conform to a Grashofian Crank Rocker, have a re-look at the summary of Grashof's criteria provided in the Introduction tab and review and re-enter your data.
Once your link lengths are validated, you are expected to find out graphically the limiting positions of the crank rocker using the Drawing Board Applet which will open when you click the link below. A new browser window will open along with the applet. Since the linkage is a crank rocker, therefore the follower link will rotate between two limits of theta 4. You are required to find those limits using this applet. The applet uses screen coordinates for drawing. Hence if you are using link lengths between 1 to 10 units it is advisable (although zoom is available for the applet) to choose a scale between 100:1 to 10:1 for easy on screen use.
To get an animated guidance of the graphical analysis using the applet click below: