Mechanical

Overall Design

The robot consists of two main layers: the top and bottom layer. The bottom layer houses the drivetrain that contains the motors, main and caster wheels, acorn collection system, and various sensors (limit switches, tape sensors and distance sensors). The top layer houses the electronic components (microcontroller, power distribution and motor driver boards) as well as batteries. Mounted to the bottom of that top layer is the acorn shooting system, which contains a high torque DC motor to drive a snail cam that preloads a spring in combination with a limit switch. This pushes a curved plate outwards to shoot the acorn from our system. The front of the top layer also houses an IR beacon with a IR-phototransistor before a signal conditioning circuit inside it to detect various frequencies. The robot also fits within a 32cm x 32cm x 32cm build footprint, and the primary construction materials are duron and PLA.

Side View

Front View

Side View

Front View

Chassis

The chassis was laser cut from 3/16" Duron sheets. It is consists of just the bottom layer, where it has holes for the drivetrain motor and pillow block mounts, as well as various sensor mounts. These mounts were all 3D printed using PLA. This layout design was intended to ensure all the drive shafts are supported at two points around the wheel, which helps reducing bending loads especially when couplers are introduced. Various patterned holes are also cut throughout the boards to route wires through.

The top panel houses all the electronics (microcontroller, motor driver boards etc), which are mounted to the top plate with plastic standoffs. The IR beacon is secured onto the front plate with M5 bolts and nuts. The acorn shooting system is mounted to the bottom side of the front layer, so holes for the corresponding bolt nuts were added as well. The game indication buttons and LEDs are also mounted to the top plate through 3D printed supports. Similar to the bottom layer, the front layer also has patterned M3 holes to route wires.

Drivetrain

The drivetrain consists of the DC motor with 3D printed motor mount, encoders, 5mm to 6mm shaft coupler, four bearing blocks and two wheels. The bearing blocks were used to minimize cantilevered loads and wobble during operation.

Drivetrain - Bottom Layer

Front Layer

IR Sensor System

The beacon is a 3D printed support structure that houses an IR phototransistor. The whole robot rotates around its central axis to track IR beacons along the field. The support structure is purposely drafted inwards to shield the IR sensor from noisy signals, and reduces the field of view of the sensor, increasing precision.

Acorn Collection System

To collect acorns, our robot uses two rotating blades, controlled by servos, to scoop the acorns into its bay and store them. They are mounted on acrylic arms that attach to the bottom of the chassis through 3D printed C-clamps. The servos follow a pull-in motion commanded by various duty cycles to get acorns from the tree.

Acorn Shooting System

The acorn shooting system consists of a low speed, high torque DC motor to drive a snail cam that slowly preloads two symmetric springs. When the snail cam reaches its lowest radius point, the spring-loaded system can push a plate out that would then eject the acorns stored in the robot's bay. The snail cam system is supported on both sides by a structure that holds bearings to reduce friction.

IR Beacon

Acorn Collection

Acorn Shooting System

Acorn Detection System

The acorn detection system consisted of an IR emitter and an IR phototransistor. The idea is that the IR emitter would emit at a specific frequency, reflect off the opto-reflective tape of the acorn and the phototransistor would detect that frequency and acknowledge that an acorn is in front of the robot. These two are mounted to the bottom of the robot to be as close as possible to the plane of the acorns.

Sensor Subsystem

The sensor subsystem consists of the various sensors used in our robot to navigate around the field. On the bottom of our chassis, 3 tape sensors were mounted to check for tape sensing to hit the tree directly in the front. An ultrasonic sensor was mounted at the bottom of the top layer to detect if any walls were hit. One limit switch was installed on the IR beacon to also help detect if a tree was hit. Distance sensors were also installed in the robot's bay to track if the robot had successfully obtained acorns.

Acorn Detection

Sensor System

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