Modern automata are crank driven mechancial sculptures that show some sort of object in motion. The design of these machines can be very complex, and requires a lot of experience. However, by the help of computer design software it is possible to make the process much easier. Over the course of several years, I have refined the design process so that models of automata can be made very fast.
Step 1: Software
The softwares used in the design process are:
- SAM Mechanism Designer
I used Solidworks for this example, but any software that allows for drawing of shapes and adding constraints are fine.
SAM Mechanism Designer is used for initial prototyping, as it is very fast for these type of tasks. The software is not free, but a demo version is available at:
Ghost-it is used for seemless transition between the other two programs. It can overlay one program window on top of an other, much like tracing paper or a lightbox. This eliminates the process of export and import and makes is possible to use the best features from both software packages. On top of that, it is free!
Step 2: Reference Material
Every good automata begins with good reference material. The reference material should contain information about shape and motion. Good sources of reference material for automata are:
- Animated .gifs
- Medical or technical drawings
In this example I will use an animated .gif of Pikachu as my reference material. I found it via Google Images by limiting the results to animated images. Animated .gifs are great because they contain only the most important positions in order to describe the motion.
Step 3: Mechanization: the Basics
The 4-bar linkage forms the basis of planar linkage mechanisms. It will transform circular motion into oscillatory motion and is the simplest planar linkage you can make.
Degrees of Freedom (DOF)
Degrees of freedom is a term that tells in how many indepentent ways a mechanism can move, or the least number of coordinates needed to describe the system.
Automata usually have one degree of freedom. If the crank is turned, all the other parts will move in a prescribed fashion. It can be shown mathematically that in order to achieve this, the total number of links has to be an even number.
Including the ground link, it can be seen that the 4-bar linkage has one degree of freedom. Subsequently, if two more links are added to a 4-bar linkage, we get a 6-bar linkage which also has one DOF. This way, a more complex machine can be created; simply by adding more and more links.
Step 4: SAM Mechanism Designer
SAM is good for initial design of mechanisms.
- Draw links with the 'Create beam element' tool.
- Fix joints with the 'Fix node in X- and/or Y-direction' tool.
- Add motor by clicking on 'Angle Input Motion' and selecting the driving element.
- Right click > 'Show path' to trace the position of a point.
- Reposition joints to achieve the motion you want.
As you can see, it is a super-fast way to experiment with linkages. It is also possible to make many other types of joints, gears, belts, etc.
Step 5: Start Simple!
Start simple! Here I started by making Pikachu's body rock back and forth with the help of a 4-bar linkage. Remember that the links can have any shape or form, it is the position of the joints that determine the behavior of the mechanism. You can make the links have different shapes by adding elements to it so that it forms a rigid triangle. For instance, I sketched out the position of the hip joint by adding two beam elements.
Step 6: Head
I made the head move by adding two more links between the body and ground. This forms a 4-bar linkage (parallelogram) so that Pikachu's head will stay parallel with the ground.
Step 7: Front Leg
Similarly, I added two more links to make the front leg:
- I changed the shape of the main body to locate the shoulder joint.
- Then I drew the leg, represented by a triangle.
- Finally, I added the link between the leg and ground.
Step 8: Rear Leg
Similarly, two more links were added to make the rear leg.
Step 9: Rear Foot
Finally, I added the two last links which formed the rear foot.
Step 10: Solidworks Layout
For creating a more detailed design, I will now switch to Solidworks. Solidworks has a feature called 'Layout' wich allows the user to create a layout of an assembly.
- File > New > Assembly.
- On the left hand side, click on 'Create Layout' in the yellow box.
Step 11: Sketch
- Trace the mechanism from SAM into Solidworks.
- Click on each element and create a block.
- Add contraints such as 'coincident' or 'anchor'.
Repeat the process for all of the links.
Step 12: Taking Shape
Each block can be edited to that they look more like the real thing. Use the original reference and trace the shape of each part. Make sure to have the correct level of zoom while tracing.
Step 13: Results
The design of the running Pikachu took less than 90 minutes, but it will of course depend on your experience and the complexity of the automata. Try it out yourself!
Step 14: Appendix
3D files, along with templates for the pikachu automaton can be found here: