Purple Rain, the robot that could, was conceptualized two days before the final presentation, built the day before, and perfected the day of. Despite this, it completed the final course admirably, experiencing hiccups only when it was run over by larger robots (which pushed it off the final ramp), and when its lightness prevented it from sliding down the final ramp. The robots durable construction also meant that despite experiencing a substantial fall at the end of the course, it was able to cross the finish line intact.
The robot features a magnetically attached, removable side for easy access to its internal construction. We added LEDs to communicate its status with users and observers, and toggle switches for  the motors and Arduino. This provides a layer of abstraction for users who prefer to stay away from the internal electronic features. That, combined with an overhauled Bluetooth control system to reduce latency, and a striking, simple, and attractive design make interactions with Purple Rain both smooth and intuitive.
We began designing Purple Rain with a MDF wood chassis prototype on the laser cutter, and a simple motor control system to prototype our gearing. The DC motors powering the robot don’t have much torque, so we took steps in our design to gear down the motors, and to make the chassis as lightweight as possible. To reduce weight in the chassis, we used the same honeycomb structure previously used in our quad-copter chassis design, and made the robot triangular, rather than square. The initial prototype also featured a cloth hinge to allow for access to its internals.
With a chassis designed, and some ideas about the gearing needs of the motors, we opted to use skateboard bearings to allow for smooth leg rotation, and put together a simple 2s battery pack to power the machine using two 3.7v 1s lipo batteries. To attach the bearing to the frame, we designed and 3D printed a hexagonal attachment. Compared to a circular one this allowed for a tight fit, while also leaving room for errors in the 3D print. For attaching the powered gear to the frame we built the gear in two layers, the bottom layer had a slot for the motor to slip into, and the top layer sat on top allowing for a flush looking gear, that hid away the ugliness of the motor.
Having completed most of the mechanical components of the design, we began designing the internals of the robot. In the end, we would have liked to clean up our internal wiring to make it neater and more comprehensible to users. However, under time constraints this was made difficult. We mounted the motors to the sides of the chassis, and fit the rest of the internals in between them. In a future iteration of the robot, the we would like to build a better wiring harness for the internals, as well as designing a system to hold the microcontroller and batteries still in the chassis better.
The design itself was built with simplicity in mind due to time constraint and wanting a clean, attainable final model. Originally, we were thinking to build a pyramid shaped box as our body. However, we decided upon a triangular prism for simplicity's sake, which still yields a dramatic effect. The colored gels were inspired by lighting in a photo studio, and the purple color was used to create an ominous effect when the LEDs were in use. Simply, each side had two gears to turn the legs with had tiny shoes painted on to give the robot some character, and to make it more user friendly. However, the details were left relatively simple to create mystery in the design and leave the users and viewers to use their imagination.
The final step in our design was to add lighting inside the chassis that would shine through the honeycomb surfaces and communicate the robots status with the users. To implement this we wired four white LEDs to the microcontroller and wrapped them in foam to diffuse their light. We then programmed them to slowly pulse on and off according to the voltage being applied to their corresponding motors. This added an interesting and informative visual effect to the robot, and wrapped up the project.
Purple Rain was built around four design goals. It needed to be simple, easy to manufacture, functional, and visually striking. The robot achieved all of those in stride. While the robot isn’t as much of a testament to technical achievement as our earlier quadcopter attempt was, it’s pleasant interface, and maintainability make it an admirable final project, all in a day's work.
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