Mechanical

Full Assembly

All CAD models of our robot were made on Fusion 360. The robot is primarily comprised of laser-cut acrylic and 3D-printed PLA.

Open the full assembly here! Warning: it is a very large file.

Design Process

Initial sketch for the first design review

Lift mechanism brainstorming

For our first design, we planned on using gravity as our primary force for moving the coal. We decided to pivot from this strategy after a TA suggestion that gravity alone is not that reliable as a driving mechanism.

Our second design sought to maximize the amount of coal we could fit on our robot at once in the hopes of minimizing trips to the dispenser.

After 3D-printing a test barrel container, we realized that this design would take up too much of the total allowed volume of our robot, prompting the shift towards our final design.

Each of the components of our final assembly were iterated on a number of times. We had three full redesigns of the container, countless modifications to the coal intake arm, two redesigns of the intake ramp, and many small iterations and reprints in between. Feel free to take a look at the version history of our full assembly to see more of our design process.

Sub-assemblies

Chassis

Robots were required to begin each round within a 32 cm × 32 cm × 32 cm cube. Our chassis was designed with 30 cm sides, leaving margin for protruding shafts and other components while still remaining within the size constraints.

The three-tiered nature of the chassis allowed for a great deal of flexibility when wiring electronics. Acrylic was chosen because it is clear, allowing visibility during assembly.

First Level Engineering Drawing

Second Level Engineering Drawing

Third Level Engineering Drawing

All dimension units are in mm. Dimensions that are arbitrary or non-critical have been omitted from the drawings above for readability.

Drivetrain

Two Igarashi 12V DC Gear Motors were used for the robot's drivetrain. PLA Motor mounts were placed on either side of the wheel to reduce bearing loads and attached to the acrylic base with screws.

The two quadrature encoders were mounted onto a singular PLA encoder mount placed between the two motors.

Coal Intake

Top view of the coal intake

A servo actuates the arm that pulls the coal out of the dispenser, and a DC motor spins the flywheel that brings coal onto the intake ramp.

The limit switch tells the robot when it has reached the dispenser.

Isometric view of the coal intake

Ramp and Conveyor Belt

Closed side view of the ramp

Side section view of the ramp(coal is shown as pink ball)

View of ramp isolated in chassis without other sub-assemblies

The flanges of the ramp allow it to support the weight of the chassis in addition to the pillars. The three primary line following sensors are mounted to the bottom of the ramp so that they can be closer to the ground than the bottom of the chassis. The ramp itself is made of PLA and 3D printed in three separate pieces to allow for assembly of the conveyor belt. The timing belt was 3D printed out of TPU and the pulleys were printed out of PLA, press fit onto 0.25" stainless steel shafts. The bushings were also custom designed and 3D printed for this assembly. The belt was driven by another Igarashi DC motor, which was mounted onto a PLA piece that attached to the third level of the chassis.

Arm

The arm (gray) consists of a laser cut piece of acrylic attached to a wooden dowel. The arm lowers the bucket (green) and then retreats back to its starting position.

Arm and servo assembly

View of container (blue) and arm isolated in chassis with arm pulling bucket (green) down

Container

View of container (blue) isolated in chassis with release of coal/balls (yellow) into bucket (green)

The container (blue) and its driving servo (black) are both mounted onto the third level of the chassis. The third level has been placed at a height above the height of the bucket (green) so that, when the container door opens, the coal will fall into the bucket.

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