4-Bar Linkage Design, Analysis, Testing

August-December 2024

1. Overview

Our objective was to create a linkage that can shine a flashlight onto five targets as quickly as possible. The targets stay in a known position, but will disappear and reappear. Therefore, accuracy and speed were necessary for a successful design implementation. This page outlines the design, analysis, manufacturing, and testing for this project.

2. Design

We optimized the transmission angle to maximize linkage speed. We determined the geometry of the linkage which meets this requirement, and we maintained this geometry throughout our design process (Figure 1). We modeled our design in SolidWorks, using cutouts in the linkage to decrease weight. Shown in Figure 2 is a detail view of the transmission design. An optimal 12:35 gear ratio was chosen based on inertia matching of the load and motor inertia to minimize the torque needed to power the linkage. Torque is transferred to the gears using a spring pin, and to the input using two screws.

Figure 1: Linkage geometry in leftmost and rightmost positions
Figure 2: Complete linkage design mounted to playing field (left) and detail view of transmission components (right)

3. Motion Analysis

Shown in Figure 3 is the linkage design exported to ADAMS. Based on ADAMS results, the linkage takes 0.69s and 0.69W to move from 87 degrees from the leftmost to rightmost position. The linkage weighs 2.5kg based on the ADAMS model. Note that the linkage accelerates until 3.5s, then decelerates until it reaches position 5. Therefore, the angular velocity, power, and torque graphs spike at 3.5s. Power is maximized at this time (Figure 4).

The ADAMS results are a theoretical model of a real life design. Therefore, a safety factor of 1.5 was used for power when determining how fast the linkage should go. This safety factor will account for power losses to friction in the motor and the joints, which were not accounted for in the theoretical simulation. 

Figure 3: ADAMS model of linkage
Figure 4: From left to right: Angular Displacement, Angular Velocity, Torque, Power (these pictures have come out very blurry, which I will try to fix in the future)

4. Stress Analysis

Stress analysis was completed in each place torque gets transferred (spring pin, gear mesh, screws connecting gears to input). Below is a sample of the analysis. 

5. Manufacturing

Shown in Figure 5 and 6 are samples of a drawing and manufacturing plan made before physically creating a part. Rather than going with a rectangular design, we removed unnecessary material and added curvature to improve aesthetics and material waste of our stock. 

Figure 5: Base plate manufacturing drawing
Figure 6: Base plate manufacturing plan

6. Experimentation

Below is a demo of the linkage CAD, as well as a video of our physical testing. We used PID for smooth control, and increased efficiency by incorporating two ways to hit target 4 (compare 0:09 to 0:25 in the second video).