ME218A - Bad Apples - Mechanical

Mechanical Design

Mechanical Design and Fabrication

Ed's Composter consists of a fairly simple wooden frame and two main subassemblies: the aerator paddle and the rack and pinion output door. The physical assembly was designed in Solidworks and fabricated using materials and tools from the PRL Wood Shop, Room 36, and the SPDL.

Material

Wood was chosen as the material for the majority of the external structure of the composter because we determined that it would be the more durable options under the high torque conditions of composter aeration. With a large volume of organic material, a paddle with a significant moment of inertia, and a high-torque drive motor, a plywood frame offered a more optimal strength and stability. as compared to acrylic or other thinner laser-cut materials..

All wood was sourced from the Product Realization Lab Wood Shop. The table saw and bandsaw were used to cut parts to size and drills were used to bore holes and screw pieces of the assembly together..

Exterior Frame

Box Compartments

Wooden Assembly

The exterior structure of the Composter is a 50 cm by 30 cm by 48 cm (Width by Depth by Height) box, split into three main compartments, as shown in the CAD image above. The right compartment houses the two motors, breakbeam sensor, potentiometer, buttons, and other electromechanical components and circuitry for the composter. The top left compartment is where the composting process occurs. Organic material is fed through a hinged door at the top of the compartment, then aerated using the large rotating aerator paddle. Finally the bottom left compartment stores the composted material, which enters this section through the sliding door between the two compartments.

The front face of the composter also contains holes for the buttons, potentiometer, and display wiring, and a large rectangular cutout for users to trigger the breakbeam sensor.

Aerator Subassembly

Full Aerator Paddle Assembly

Aerator Paddle Profile

The aerator paddle subassembly consists of a motor coupled to an aluminum shaft with three 3d printed paddles attached. The entire assembly spins (within two bearings) and displaces organic material from the bottom of the composting compartment to the top of the pile, thereby introducing air into the composting process.

The output door subassembly is a rack and pinion mechanism connected to an acrylic panel that splits the top and bottom compartments of the composting process. The full assembly consists of a motor connected to a pinion gear coupled to a gear rack. This gear rack is connected to a large panel which sits on 6 roller wheels. As the motor drives the pinion gear, this causes the gear rack and door to shift backwards; the door rolls on the roller wheels and is pushed out of the way such that the composted material can fall through to the last output compartment.

Output Door Subassembly

Door on Rollers

Rack and Pinion

The output door subassembly is a rack and pinion mechanism connected to an acrylic panel that splits the top and bottom compartments of the composting process. The full assembly consists of a motor connected to a pinion gear coupled to a gear rack. This gear rack is connected to a large panel which sits on 6 roller wheels. As the motor drives the pinion gear, this causes the gear rack and door to shift backwards; the door rolls on the roller wheels and is pushed out of the way such that the composted material can fall through to the last output compartment.

Drawings

Download CAD and Drawings