Step 1: Collect Materials
x3 Limit Switches
x4 DC Motors
Gear Boxes for motors
Screws and Nuts
Arduino Motor Shield
Other metal pieces and miscellaneous parts
Step 2: Identify Methods of Sorting
Since the Tin can is the only container that is ferrous, a method to test if a material is magnetic will be developed.
Now that the Tin can now be identified, the Aluminum can is the only remaining material that will conduct electricity. A method to test for conductivity will be developed.
The remaining two materials can be sorted by measuring their lengths. In the contest rules, the size of each bottle/can to be sorted is given. The biggest glass bottle is smaller than the smallest plastic bottle. This leaves a gap between the two materials' lengths. A method to test the lengths of the bottles will be developed.
Magnetic Test: The method to identify the Tin can is to use a magnet switch. A magnet is placed onto a hinging metal bar that is resting on another piece of metal. When a tin can is past over the magnet, the magnet is attracted to the can, which pulls apart the metal pieces. The metal pieces act as a switch. When the magnet is attracted to the can, it opens the switch.
Conductivity Test: The method to identify the Aluminum can is to use a conductivity test. Two metal plates are placed on each side of the can. One of the plates will move and contact one side of the can and then push it into the other plate. The two plates will also act like a switch. When the Aluminum can comes into contact with both plates, the switch will close.
Length Test: The method to differentiate between the glass and plastic bottles is to use a length test. The two metal plates used in the conductivity test can be used in this test. When they touch each end of the glass or plastic bottle, the conductivity switch will be open, but the distance between the two plates is the length of the bottle. An ultrasonic sensor can be used to measure the distance between the two plates. If the length is within the smaller bottle size range, it is glass. If it is within the larger range, it is plastic.
Step 3: Build Machine Frame and First Testing Area
As the bottle/can moves along the conveyor it will fall of the end. A limit switch is attached at the end of the conveyor to signal to the Arduino when the bottle/can falls off the conveyor. This will also signal the Arduino to stop the conveyor.
Step 4: Build Second Testing Area
Another plate is attached on the other side of the frame, opposite of the moving plate. This plate is attached with hinges at the top of the plate. A limit switch is placed behind this plate. When the bottle/can is pushed into this plate, it will pivot and push the switch, signaling the Arduino that the bottle is touching both plates and to stop the motor. A wire is attached to each plate to create the conductivity switch. An ultrasonic sensor is also attached to the pivoting plate. It will send a signal that will bounce off of the other plate, measuring the length of the bottle/can between the plates.
When these tests are completed, the moving plate will be moved back out to its original position. Another limit switch is placed at this position to signal when the plate has returned and to stop the motor. At this point the Arduino will know if the bottle/can is glass, plastic, Aluminum, or Tin.
Step 5: Sorting Ramp
To get the bottle/can to the ramp, the bottom plate (blue plate) in the second testing area is actually a trap door. When the ramp is in the correct position, a motor will rotate the trap door out of the way, causing the bottle/can to fall down and hit the ramp, diverting it to the correct side of the machine and into its bin.
When the bottle falls into its bin, the trap door closes, the ramp returns to the starting position, and the machine starts over by running the conveyor.