「SHEER HEART ATTACK」
Class: Autonomous Mobile Robots
Year: Fall 2018
GOAL: create an autonomous robot to participate in a game of "robot football"
RULES: two robots must navigate a walled-off course filled with obstacles and shoot ping-pong balls at the opponent's robot or their goal, each fitted with an IR beacon to allow tracking with IR phototransistors.
FEATURES:
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Ultrasonic sensors to detect obstacles
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IR sensors to detect IR beacons (attached to both robots and both goals)
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Magnetometer to detect the orientation of the robot, to differentiate between our own goal and the opponent's
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Ball launcher using a spring-loaded rack and pinion mechanism
THE DESIGN:
The inspiration for the design of this project is the autonomous tank of the same name from popular manga series JoJo's Bizarre Adventure. It tracks targets via their body heat through infrared vision, much like how our robot detects opponents using IR photodiodes.
A major self-imposed design criterion for this project was to make it as similar as possible to its namesake, while still fulfilling all of the technical requirements of this project. The goal was to create a product that does not need to sacrifice its looks for full functionality.
Sheer Heart Attack as it appears in JoJo's Bizarre Adventure: Diamond is Unbreakable
TECHNICAL DETAILS
The robot's body was designed in OnShape to be manufactured using laser cutting and 3D printing. 1/4" acrylic was used as a baseboard. The entire outer hull was 3D printed and attached to the top and bottom of the acrylic. The baseboard and hull form a two-layered chassis, on which other components could be attached.
The motors and the cannon are mounted underneath the robot. As the top of the hull is relatively enclosed, the Raspberry Pi is also mounted on the bottom to aid in ventilation. This makes it easier to access as well.
The robot is powered by two rechargeable batteries. A 5V battery powers the Raspberry Pi and the servo for the cannon. The motors are powered by a separate 12V source. We chose to use high-capacity rechargeable batteries, which took up a lot of space inside the robot. As such, we needed to streamline our wiring to prevent a cramped interior.
Click images for more info
The Cannon
The cannon uses a spring-loaded rack-and-pinion mechanism to fire a ping-pong ball. The mechanism is actuated with a continuous-rotation servo motor, used to pull back the rack. A ratchet bar was implemented to restrict the rotation of the pinion, minimizing the load on the servo motor. The entire cannon body and mechanism is 3D printed. The back half of the cannon is used to support the rack when it is extended in a loaded position. Additionally, the caster wheel is mounted to this support. The skull attaches to the front of the barrel through a friction fit, with the ping-pong ball shooting out of the robot's mouth.
The Sensors
The robot uses five ultrasonic sensors to detect obstacles, and seven IR phototransistors to detect the infrared beacons on enemy robots and goals. The first layer of the chassis was designed to fit four of the ultrasonic sensors. The IR phototransistors are mounted on the second layer of the chassis using laser-cut inserts that can be mounted at various angles. The two front-facing sensors were mounted on the skull.
The ultrasonic sensors could be connected directly to the digital pins of the Raspberry Pi, but the phototransistors - being analog devices - needed to be connected through an 8-channel ADC which allows all 7 sensors to be read simultaneously on 4 digital pins.
