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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.
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. 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.
Electronics and Software
For the motor speed control, simple H-bridge boards were used - one for the back wheels and one for the input crank. Along the way, we faced a problem powering the main crank motor due to the Arduino board being unable to provide the higher voltage required. For this reason, we connected the crank H-bridge directly to the wall socket, and this voltage was then stepped down for other parts to operate. Besides this, since the aim was to achieve simplicity in the electronic and software system, no other major issues occurred.
On the software side, we had to manually tune the speed and the duration of the motor activation as it did not contain an encoder. After many attempts, we reached an approximate point where the motor would reliably rotate one full rotation for the parallel parking. Additionally, an unforeseen problem with the dwell occurred, in which the gears got stuck during the transition between the dwell and movement. To compensate for this behavior, we added a simple jerk motion to the crank motor. Although this was not aligned with the initial goal of simplistic software, it was too late to fix the hardware design and reassemble the whole mechanism.
Final Prototype
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.
Conclusions and Future Works