Automatic Can Crusher

Need of the Product:

As students, we have to live in small spaces such as dorms and studio apartments. We always have to find ways to save room and keep things clean. Therefore, having a machine like a can crusher can come really handy to help us save space, keep tidy and organized and of course, help the environment by recycling. Almost all of us drink sodas, canned beverages or canned food. These cans can quickly pile up to eat our space. . Instead of putting the empty cans in the trash bag and throwing them away, compressing those cans allows us to easily take them to an aluminum recycling place which can also get us some extra cash. This will also help recycling our cans.  Most of the cans are made of aluminum. Recycling of aluminum cans saves 95% of the energy required to make the same amount of aluminum from its virgin source. 

Overview:

For our can crusher machine, we are using a slider crank mechanism to crush the cans. The slider-crank mechanism is a particular four-bar linkage configuration that converts rotational motion to linear motion. We will have a motor to rotate the crank which will cause a linear motion in the piston. The linear motion of the piston will produce high enough force and torque to crush the cans. Slider crank mechanism provides significant advantages such as low cost, reduced number of parts and reduced weight. Our product will have a platform to hold as many as 5 cans which will then be crushed one by one in seconds. Using a can crusher to reduce the capacity of waste materials is a great way of cutting the expense of waste transport.

Specifications:

1. System must be able to feed cans individually and autonomously into a slot to be crushed. These cans should then be automatically disposed before retracting for the next can.

2. System must be able to retract cleanly without impacting the rest of the system.

3. System must provide enough mechanical advantage to crush each can.

4. Crusher needs to reach 250 pounds of force to adequately crush each can.

5. Each can needs to be of standard 12 oz size and in uniform shape before fitting into the feeder, as detailed below.

Description of Final Design:

For this project, we are designing an automated can crusher which uses a slider crank mechanism to crush cans automatically. Our can crusher is operated by a motor which rotates the second link of the mechanism which we call the crank. The crank is connected to the third link which is then connected to a slider that slides along a rail and eventually hits the dropping cans to crush them.  We are utilizing gear ratios  in our mechanism to produce high enough torque that is required to crush a regular soda can. Our whole design can be divided into 3 sub-designs which are integrated to make the whole product. The main sub-designs are as follows:

The platform and rail:

For our platform, we have a top opening for the cans to be fed into our system to be crushed as shown in the picture. The system will utilize this feeding channel to drop each can at the same angle and position to keep the system tolerant to jamming.  As the user feeds cans to our product from the top opening, gravity will help the cans to fall on the space one by one, where the slide will slide with high force and torque to crush them. There is a rail system along which the slider will slide. Once the user turns on the switch, the mechanism will be activated and the slider will start sliding along the rail. We have a strong wall on the back of the platform on which the can will be crushed against. The wall is made from extra layers of thick wood to withstand the impact from the crushing mechanism The system can also easily be integrated into a large structure by placing it against the wall of a larger structure, minimizing the wear on the back wooden support. After the can is crushed, our system has a small opening on the button from which the crushed cans will fall through. As the system retracts back to the original toggle position, the slider leaves the can chute, allowing a new can to fall into place. After the toggle, the system can continue again with a new can to crush, creating an infinite cycle of automatic crushing and disposal. 

Motor and Gearbox:

The goal of our project is to create a product that can be functional in most normal houses. Therefore, a common AC motor that functions with 120 voltage, and can be found in many household appliances is an ideal choice. Nevertheless, our application requires a high power motor that is able to provide enough torque to crush a can. Most high power motors (with power value being larger than 0.5 horsepower) come with high angular velocity. Thus, we designed a gearbox to reduce the angular velocity to the desired rate for safety as well as time efficiency. Additionally, as angular velocity decreases via gear reduction, the final output torque increases significantly to meet the torque specification listed above.

Links and slider:

We have manufactured the links from plywood using a laser cutter. The output shaft from the motor is connected to the second link with the help of a ball bearing. The second link is connected to the third link by a ball bearing and shaft for smooth rotation. The shorter link (link 2) is 3 inches long while the longer link (link 3) is 8 inches. This creates a system where the slider (link 4) moves a total 6 inches from each toggle position. As the standard soda can is 4.8 inches, this is plenty of room to crush the can to a compacted size while still providing enough backstroke for an additional metal can to fall into place after crushing is complete and the first can is removed. The third link then connects to a piston which will be crushing the can. The piston has an eye bolt in the back that helps in the easy attachment of the third link to it. We have used 1/16 inch steel sheets on the face of the piston that will hit the cans as shown on the picture above. This design of metal face adds more rigidity so that the force from it is strong enough for crushing and increases the lifespan of the slider mechanism considerably. To ensure easy kinetic motion as the slider moves through the system, two T-slotted rails are built into the base of the mechanism below the slider. By drilling holes through the entire slider and inserting a long bolt, T-slotted rail sliding nuts can be attached to connect to the rail itself. With this system in place, the slider is able to move smoothly and minimizes any perpendicular force on the rail system. By having the slider rails in place, the system lifespan increases and the risk of jamming is heavily reduced.

Discussion and Future Plan:

By our considerations, our project was mostly successful from a design standpoint. The manufacturing process was simple and efficient and no outstanding issues were encountered during assembly. Regrettably, our system was unable to crush a standard soda can in each rotation. Our system is designed with materials capable of withstanding the load applied and a motor outputting 672 in lbs of torque, almost double what is required to crush our can. The failure in the mechanism occurred in the gearbox, as our system used plastic gears for prototyping that slipped and could not be tightened further without breaking the gears. Were metal gears used in its place, the system would destroy itself before stalling on the impact with the can. For future prototypes we would switch to metal gears but in our initial design we could not afford the financial cost of all the gears required in metal. Durability was a major concern for our design and we were able to successfully ruggedize our system against the repeated forces of the crank slider mechanism. With the exception of the gear slippage, our gearbox worked successfully and provided more than enough force to prove the system concept. In future designs, we would probably slow the motor down even further to ensure there is significant time for a new can to fall into place after each oscillation. The feeder mechanism and disposal slot worked without failure and future models could extend the height of the feeder to allow for more cans to be crushed at once before restocking.