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Video 1. Four-bar linkage simulation.

Computer-Aided Design

The CAD of this project was done via Solidworks. Our team utilized the simulations in Solidworks to test our ideas and verify that the gear ratios we calculated before indeed generated the desired output motion. Furthermore, it allowed us to identify potential problems in advance, which would increase the efficiency of our manufacturing and assembly processes. 

Figure 6. CAD assembly.

Video 2. Machine simulation.

Figure 7. Engineering drawings of different parts.

Manufacturing and Assembly

The linkage synthesis and analysis were done rather swiftly, and most of our effort went into manufacturing, assembling, and debugging. We first cut the base plate and attached the four-bar mechanism as a starting point. Although this was originally intended as a placeholder, as the design progressed, we stuck with the original base plate. After that, the holes for the gears, motors, and wheels were drilled, and the gear train was mounted on top. Since most parts were laser cut, their dimensions were not exact, and we had to recreate the same part with minor adjustments continuously. Due to this reason, bearings were omitted to allow for a more simple procedure, which was tolerable as the friction in the joints was not quite high to cause operation issues.

Figure 8. Basic assembly.

After this point, the wheel mounts and housings were printed and then mounted alongside the parallel four-bar mechanism that linked the two front wheels together. Similarly to links, the gears had to be cut multiple times as their alignment had to be quite more precise than other mechanical parts. Our team decided to cut multiple sizes of gears, which differed only in small increments from each other, to ascertain the best fit for the gears to be meshing with each other smoothly. Before mounting and connecting any of the electronics, we tested the mechanism by hand cranking it to ensure that our hardware was functional. The dwell mechanism was added later by grinding away some of the teeth in the driver gear. At a neutral position, this allowed the car to drive freely using the previously established joystick control.

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On the day of the presentation, our car was able to achieve a near prefer parallel parking on the first attempt. However, due to roughly tuned software, the car was not able to reliably recreate this result in the subsequent runs. Overall, we deem our design and concept to be a success, although the mechanical assemblage can use a rework. 

Video 3. Final presentation.

Conclusions and Future Works

Reflecting on our project, one area that we could have improved upon is the mechanical hardware to make the prototype more robust. Professor Deshpande pointed out in the demonstration that the rotation of our revolute joints would be smoother if we had used bearings and unthreaded screws. Furthermore, due to some of our parts being 3D-printed, the tolerances of through holes could have been better, which would result in less play between some of the connections. As for the gear teeth, we could have enlarged the size of the gear teeth by the kerf of the laser cutter itself. This would allow a better meshing and may have prevented the situation of gears being stuck during the transition between dwelling and movement. If the gears were laser cut with some parts of the teeth taken out prior in the Retina Engrave design, that may have made the transition more accurate as well. With more experience, we would have also been able to foresee the problems powering the main crank motor and address that ahead of time. If we were to upgrade our prototype and improve it further, one potential area we could explore is that of making an autonomous parallel parking robot. We could attach ultrasonic sensors to measure the distance away from the parking lot, which would be converted to motor inputs so that the car can park itself, regardless of how far it is away from the parking lot. In conclusion, we believe that this project was a successful and fruitful one, where we achieved our original goals and learned many insights about mechanical design and robotics along the journey. 

Appendix

(Bill of Materials.)