06.4 Implementation - Orange Juicer
Fabrication
Due to the design and magnitude of forces involved in juicing an orange, it was decided that the main body of the juicer would be made out of 1” steel tubes. All other fabricated pieces for this project were 3D printed due to it being the easiest and most accessible fabrication method for our team.
Metal Fabrication:
The metal was sourced from McMaster-Carr as a single 3 ft long piece. The first step was to cut the bar into the needed lengths using a drop saw, four 4” long bars, and one 16” long bar. After this, a manual mill with a DRO was used accurately drill the required mounting holes in the bars. Once all dimensions were checked and confirmed, the five pieces were welded together.
Additionally, a manual mill was used to face one of the steel axles, turning it into a D-shaft for better power transmission.
Welding Jig
In order to have the welded structure have correct dimensions, a jig method was devised using circular pucks to constrain the pieces. The pucks would be attached to a 1x1” hole optical table using quarter inch shoulder bolts. They were 3D printed out of PETG and were successful in constraining the components together to be properly welded.
|
|
|---|
Assembly
In order to assemble the juicer, first, the head piece was mounted to the metal body using screws through the designated holes. Then, the motor shaft was slotted through the hole on the bottom of the head and the motor was fastened in place using the mount build into the head. After securing the motor, one of the miter gears was attached to the shaft and it’s set screw tightened through an access hole on the side of the head. Next, a long shaft was run through the side of the head, with a miter gear attached in the center.
Once the main components of the head were assembled, the linkage was attached. First, each link two was mounted to the main shaft using built in shaft collars. Shorter shafts were then attached to the second holes in the link 2 pieces, bearings were placed on each axle, and the link 3 pieces were attached and held in place using shaft collars. A similar process was then repeated to connect the link 3 pieces to the orange holder.
Next, the pieces making up the ejector assembly were fastened to the metal body with screws and a chain was used to connect the sprocket at the bottom and link 2. The bottom slider was also fastened directly to the metal body.
Finally, the cup mount was screwed into the two metal feet at the bottom, and the cup fastened in place.
Electronics
Main Circuit
For the electronics portion of the project, a motor speed control circuit was devised to run our DC planetary gearbox motor. The circuit would use an Arduino Uno R3 microcontroller, an Electronic Speed Controller (ESC), and a 7.2V battery. The circuit would also include a breadboard and button for manual operation of the entire juicer. The electronic control portion would be to drive the motor at a controlled voltages using pulse width modulation (PWM) signaling.
Since the motor pulls up to 25 A, and the Arduino is limited in amperage pull per output pin up to 40mA, the Arduino cannot directly power the motor otherwise it would damage the microcontroller. This is the reason behind using the ESC within the circuit, to handle the high current pull from the battery to the motor.
For the first iteration of the circuit, the breadboard and button were absent as they were not needed to confirm that the circuit could be wired up and powered using the battery and controlled using the Arduino.
Wiring
The circuit was assembled using the selected electrical components of the motor, ESC, Arduino, breadboard, button, along with male to male jumper cables and XT30 connectors, male and female.
For battery and ESC connectivity, XT30 keyed connectors were attached on for their small scale size and ability to handle 30A continues current, which is rated above the max current draw of 25A from the motor. The keyed part served as a safety measure to ensure we would not short the circuit by plugging components together incorrectly.
The circuit was assembled connecting the battery and the motor to the ESC, then from the ESC the Arduino is connected with the ground and digital PWM output pin 9. The power cable is routed from the ESC to to the breadboard, which is connected to the button, and from the button goes to the Arduino Vin power input. Since the ESC was built for two motor outputs, the two ends were soldered together and connected to the motor.
Arduino Control
For the code, there was a target voltage that could be set to control the speed of the motor by using the Arduino's servo library to send a PWM signal to the ESC. When the button is pressed and the circuit connects, it waits 2 seconds to allow the ESC to boot before beginning the powering sequence, holding power for another 2 seconds so the ESC can initiate properly. Once fully powered, the motor spins until the button is released.