2. Project Design

4 Bar Mechanism

The dinosaur head automata can be described by the vector loop labeled in Figure A. In order to model the kinematics of the mechanism, I started by identifying a four-bar linkage at the base of the extender. Each of the ternary links of the extender can be separated into two vectors. In the following diagram, vector R2 is the input. R2 is controlled by the crank located on the backside of the block. 

I formed a vector loop equation using the crank, two bottom extender linkages, and the ground:

R2 + R3 - R4 - R1 = 0

The kinematics of the other vectors were then calculated based on the angles of R3 and R4. As you can see, vector R3 shares an angle with each vector shown in light green and dark blue due to the mechanism's geometry. Likewise, vectors shown in pink and light blue have the same angle as vector R4. From this relationship, I was able to find the values of interest which were:

1) positions of P1, P2, and H

2) angular velocity of P1 and P2

3) forces of P1 and P2

Figure A. Vector loop of dinosaur head mechanism

Building the Dinosaur

The following materials were used to build the dinosaur mechanism:

• 6 x Skinny Wooden Craft Sticks
• 8 x Mini Brass Brads
• 1 x Paperclip
• 1 x Thumbtack
• Scrap Paper
• Piece of wood leftover from our hands-on project from the beginning of the semester

To build the device, I cut each wooden craft stick to a length of 2". I then made holes in the appropriate positions on the stick with a thumbtack. Mini brads were used to form the joints of the linkages. A small thumbtack holds one linkage of the extender to the base piece, while a paperclip was used to make the crank linkage that also connects another linkage of the extender to the base. Two paper cutouts were taped at the end of the extender to model the dinosaur's head. The final product can be seen in Figure B.

Figure B. Assembled dinosaur head automata mechanism