Shawn Pierce's Final Report
I have been calling my robot "The Manticore". It gets its name from the fearsome beast which has the body of a lion, the tail of a scorpion, and the wings of a bat (only much larger). While my robot does not have wings or a poisonous tail, it will have a stride that I imagine is much like that of the Manticore.
Physical Model Design
My goal was to build a four legged robot which would be powered by two motors. Each motor would power two legs on its side of the robot. The legs would move in a locomotive motion to allow the robot to walk.
An Early View of the Frame
A Top-down View of the Body
A Diagonal View of the Body
Technic Lego Parts
2 Lego Motors
2 9-Volt batteries
I built a more sturdy leg structure for my robot which would be able to hold more weight. Also I found that the legs of the robot would need to be staggered to allow for a stride that more closely mimics that of a cat-like animal.
Side View of the Manticore
This is a ZIP file which contains the MOV file for the side view
This is a ZIP file which contains the MOV file for the front view
Virtual Model Design
I decided upon using MSC Adams View for both model assembly and simulation. I found that of the choices available (Microstation, I-deas, and Solidworks) it seemed to be the most intuitive as far as the interface.
Building the Model
I began constructing the model using the primitive solid parts that are available in Adams. I found this approach to yield fairly decent results. However, as I began to precisely arrange the pieces, I found that this method was very ineffective and very slow. I decided to start again, but this time I used Adams primitives called a "control points". There is a menu where one can specify the X, Y, and Z values for a control point exactly instead of "eyeballing it". I then placed a series of control points on an empty scene, which I then was able to simply move parts and align them to the control points.
Once all of the parts were in place, there was the matter of connecting them. To join two objects in Adams you add a part called a "joint". There are revolute joints and fixed joints. Fixed joints will simply adhere parts to each other. Revolute joints will allow the parts they attach to rotate relative to each other with respect to 1 axis. Again I was able to make use of the control points to place the joints at the exact centers of the rotating portions of the model.
Simulating the Model
The model simulation tool is built into Adams View. To set things in motion with the virtual model, I had to apply a rotational force to the revolute joints and also set contact forces between each of the legs and the ground. Then during the simulation, each of the model viewing commands (such as zoom, rotate view and translate view) were still available for recording the animated model.
A Side View of the Robot
A Front View
A Top View
A Diagonal View
This is a zip file with the manticore model file for Adams™(.bin)
What I Have Learned
In my first design I did not take into account the fact that, if I placed gears a certain way, the robot might step forward with its front legs, and then backwards with its back legs. This was easily fixed by adding one gear to the back legs, which reversed their motion.
Axles and Leg Synchronization
Not only did each side's legs need to be out of sync, but also each side needed to be out of sync with the other. This was important because otherwise the robot would just stand in place and swing the body back and forth. By placing an axle from the left side's gears to the right side's I was able to synchronize both sets of legs.
Another problem that I ran into was that, after I completed my design, I found that one motor was weaker than the other. Using the axle helped to distribute the rotational force more evenly.