Mechanical
Top Level Design
The goal of our mechanical design was to build a robot that was not only capable of navigating the field quickly, but also sufficiently modular so that we could adapt our game strategy during the course of the project. To achieve this, we adopted a two layered construction.
The bottom layer was designed to house and protect all the sensors and mechanical elements needed to move the robot, such as the motors, H-bridges boards, and the ultrasonic sensors and tape sensors. We also included mounts for additional reflectance sensors and encoders, even though we did not include these elements in our final control strategy.
The other electronics were mounted on the top layer so that they could be easily accessed during prototyping and testing. In addition, the top layer includes the IR sensor for beacon detection, the three user input buttons, and a panel for the light and servo indicators.
The robot was constructed almost entirely out of 1/8" Duron, except for the edge bumpers, which were 3D-printed.
Engineering Drawings
ME218BFinalDoc.pdfFinal Assembly
Chassis and Drivetrain
The figures below show the layout of the drivetrain. The four wheels were attached to the bottom plate in a diamond configuration, with two 80 mm wheels attached to the motors at the robot's sides and the two casters mounted at the front and back. The caster wheels were mounted slightly offset from the ground to maximize the distribution of weight of the robot over the driven wheels, which helped prevent slipping. Finally, the diamond configuration allowed us to perform rotations along the center of the robot when switching lanes.
The wheels were attached to the motor using a D-shaft and a shaft coupler. To minimize side loads being transmitted to the motor shaft, two bearings were used to support the D-shaft.
Sensors
Ultrasonic sensors were mounted to the bottom platform at the sides and back of the robot. To make sure the ultrasonics sensors were not damaged during collisions, the transmitter and receiver of the ultrasonic sensors were slightly recessed from the exterior surface of the bumpers.
The line sensors used for tape following were directly mounted to the bottom of the chassis, while the line sensor used for lane detection was mounted using a 3D-printed piece that could be mounted lower to the ground. This gave us better sensitivity when repositioning.
The IR sensor was attached to a 3d-printed piece that narrowed the sensor's field of view so that it could only sense one beacon at a time. This piece was attached to a Duron stand located at the front of the robot.
Other Design Features
To win merge battles against other teams, we mounted the heaviest components, the batteries, vertically over the driven wheels. This maximized the torque our robot could generate without slipping.
Finally, to withstand frequent collisions with the commits, we used bumpers constructed out of two layers of duron. The bumpers were press fit between the top and bottom layers and could be easily be adjusted by tightening the supports of the internal duron pieces attaching the top and bottom places.
