Mechanical

Overall Design

The robot uses a grabber arm to collect coal from the game dispenser and deposits the coal in the robot bucket. The robot bucket rotates outwards from the robot and dispenses coal in the game buckets. Two wheels driven by DC motors and a ball caster wheel are used to move the robot. Integrated sensors enable navigation: (1) five reflective sensors for tape detection, (2) two limit switches to detect collisions, (3) one IR distance sensor to detect wall proximity, and (4) one IR phototransistor to detect the game board beacons.

All CAD models were designed in Fusion 360 (full assembly embedded below) and technical drawings are in millimeters.

Physical Robot Isometric View

CAD Model Robot Isometric View

Top View

Back View

Right View

Bottom View

Navigation

Chassis

The chassis consists of two layers of 1/8'' laser cut Duron, with the second layer mounted using 3D printed standoffs. Since the bucket extends over the inner edge of the upper level of the chassis, the upper level is around half the length of the lower level. Holes were cut out across the chassis layers for any wiring needs.

Drivetrain

Off-the-shelf components (wheels, shafts, couplers, bearings) were used to assemble the drive train. The motors are mounted using 3D printed PLA components at the back end of the robot, and a ball caster wheel is mounted in the center front for balance. Encoders are attached to the back of the DC motors using 3D printed PLA parts.

Collect

Grabber Arm

To collect coal from the dispenser, we designed a grabber arm that mounts on a 35 kg-cm torque servo at the base. The servo rotates the grabber arm between the collect (parallel with ground) and release (around 90º upwards) positions. A rack and pinion mechanism driven by a 20 kg-cm torque servo is used to open and close the grabber, which can collect one piece of coal at a time. A mini ramp is integrated into the grabber to facilitate the release of coal into the robot bucket. All custom components of the grabber are 3D printed using PLA.

Arm raised (release/ready position), grabber closed

Arm down (collect position), grabber open

Dispense

Bucket Arm

The bucket arm rotates over 180º using a 35 kg-cm torque servo. During rotations, the bucket remains upright through a freely rotating dowel pin connected using bearings to the arm. A funnel is attached to the top of the bucket to ensure deposited coal fall inside. The inside of the bucket is partitioned into two halves. A continuous rotation servo is embedded inside the bucket to create a rotating bucket bottom, allowing for two dispense sequences. Each custom component is 3D printed in PLA.

Bucket in collect position (waiting for coal)

Bucket in dispense position

Bucket bottom, closed

Bucket bottom, first dispense

Bucket bottom, second dispense

Pusher Arm

A pusher arm is mounted directly to the side of the bucket. This arm rotates outwards using a 180º servo during the dispensing sequence to lower the target game buckets. The arm and servo mount are 3D printed in PLA.

Pusher arm drawing

Pusher arm, up

Pusher arm, down

Sensors and Indicators

Line Sensors

Five line sensors are mounted to the bottom front of the robot with a 3D printed PLA holder. The sensors are spaced one tape width apart such that only the center sensor will detect tape during line following.

Side Indication Flag

A 180º servo is used to indicate the side of the game board the robot is on. The servo is mounted on a 3D printed PLA stand with signs for green/blue attached to the sides.