II. Design Process - CZ
I began my design process by referencing the example leg layout included in the Klann Linkage Wikipedia Page. However, that layout only provided the xy coordinates of each joint so I had to calculate the leg lengths in order to create the actual leg model. Show below is the analysis that I performed to find all of the necessary lengths and angles for the legs.
Figure 3 – Klann Linkage Analysis
I performed kinematic analysis of the Klann linkage in Matlab and found all of the leg lengths and angles for the base configuration. (Code is in the appendix)
leg_lower = 8.9654
leg_upper = 8.9661
arm_outer = 5.2205
arm_inner = 5.9
rocker_upper = 5.1764
rocker_lower = 3.2062
crank_length = 2.68
triangle_outer = 8.6874
triangle_inner = 6.5859
triangle_lower = 6.1569
leg_angle = 30.003
arm_angle = 12.838
triangle_lower_angle = 16.61
From the calculated values, I created a CAD model of a prototype Klann linkage leg. I built the CAD model around a reference sketch and used global variables since they will make it easy to change parameters in the future as I make adjustments to the leg. For example, when I originally designed the leg, I made the bolt holes for M5 bolts but I realized that the bolts that I already have are M3. Because of the global variable that I used, I only had to update a reference document and all of the linkages automatically updated with the new hole size.
Figure 4 – Klann Linkage CAD Model
I chose to design the entire robot to be lasercut since that would be the fastest way to quickly make changes to the robot during the assembly of the robot. 3D printing the robot is also possible with the CAD models but would have taken significantly longer to create. For lasercutting, I had the option to use 1/4" or 1/8" wood or acrylic. I decided to use wood since it is both cheaper and more durable than the acrylic. I opted to use 1/4" wood both because of the strength required and the additional thickness that the 1/4" provided for bolt clearance.
I decided to use bolted joints since that would be the simplest joint to implement on the robot. To limit the amount of friction between the wooden linkages, I added nylon spacers between each spacer and link. One significant challenge with the mechanism was organizing the legs and spacers such that the bolts in the joints would not run into the linkages during the leg's motion. To solve that problem, I added lasercut spacers to the assembly which offset the linkages and provided bolt clearance.
Figure 5 - Bolted Joint Assembly
Before building an entire robot, I created a lasercut testing stand to validate the joint and leg design. The stand consisted of a single leg linkage attached to a fixed base shown in figure 6 below:
Figure 6 – Leg Linkage Test Assembly
Next → III. Kinematic Analysis and Synthesis