Fabrication and Assembly

After our initial prototype was made, we found that there were some minor issues and adjustments that needed to be made. First off, we realized that press fitting our 2 ternary links to a regular, cylindrical shaft would not be enough to align them in tandem perfectly across all movements of the mechanism, so we decided to update our ternary shaft to be a D-shaft instead with shaft collars on both ends. 

Figure 1. D-Shaft CAD

Figure 2. Ternary Link Assembly CAD

In addition, to updating the connection between our ternary links, we automated our mechanism with the addition of a power supply, an L298N motor controller, and an Arduino, and we replaced our hand crank with a 12V DC motor for the input link. We created CAD models of mounts for the Arduino and motor to fix them onto our base plate.

Figure 3. CAD of electronics, mounts, and base plate

Finally, we increased the thicknesses of all our links to improve overall link strength and added a modular end effector to the end of our modified pink link. We decided on adding this end effector for our final design as it allowed for flexibility to adjust how we wanted our ball to launch on contact. Additionally, we adjusted the shape and size of our top base plate for increased transparency and design compaction, and added a bottom base plate for overall rigidity, adjusting the shape of our standoffs accordingly. The final CAD with all of our changes is seen below:

Figure 4. Linkage and end effector CAD - Side View

Figure 5. Linkage and end effector CAD - Trimetric View

Figure 6. Final Prototype CAD - Top View

Figure 7. Final Prototype CAD - Isometric View

Figure 8. Final Prototype CAD - Front View

We manufactured the D-shaft by hand with a manual mill according to the specified dimensions on our CAD, though as with any process, nothing is perfect. The two ends were different from the dimensions in the CAD, meaning that we had to play around with the tolerancing of the ternary shaft press-fit slots until we had a tight enough connection. For the links and base plates, we recut them with 1/4" acrylic. We 3D printed the grounds, standoffs, end effector, and mount for our motor and Arduino.

Figure 9. D-Shaft and Ternary Link Connection

Figure 10. D-Shaft Manufacturing

Figure 11. Final 3D Prints and Laser-cut Links

To mount our ball, we needed a solution that would allow for free motion of the ball once it is hit, similar to how a golf tee normally falls after impact from a club.  With tips from the TAs, we chose to source rubber golf tees for our solution. This solution ultimately allowed us to calibrate the position at which we wanted our ball to be hit, and it also ensured that we would have a robust method to hold our ball. Additionally, the team printed additional 1.1" standoffs in order to optimize the height at which the end effector made contact with the ball.

Figure 12. Ruber Golf Tee

Hardware

The hardware components utilized in this design are a 12V DC motor, a power supply, an L298N motor controller, an Arduino, and a potentiometer. 22 AWG jumper wires were used to connect these components together to form the circuit below. Note that the L293D acts as a placeholder for the L298N.

Figure 13. Circuit Diagram

Software

The team integrated the hardware components into the final prototype using an Arduino. The code involved reading the analog signal from the potentiometer in order to adjust the PWM signal to control the motor. The final code can be seen below.

Figure 14. Arduino Code