Can Cover Rotation Design

Shaker Can Cover Rotation

Design: In order to dispense steadily, we would like to come up with a way to rotate the shaker can cover reliably. Our final design, as shown in the figure below, uses the micro servo to control the rotating cover, as they are relatively easy to control and has a horn which can be attached to the rotating cover using superglue. To integrate the design into the framework, we added three more furring strips to the framework and secured the micro servos to the furring strips for effective rotation of the covers.

figure 1	figure 2

The center of the can cover is drilled out to attach the servo more easily. Figure 1 and Figure 2 show the physical attachment between the micro servo and the shaker can cover. More specifically, the micro servo has three available positions, left, center, and right. To control the position, we output PWM signals to the GPIO to which the servo is connected. Figure 3 shows the input waveform range for our micro-servo. When the duty cycle is set to 1.5ms, the servo is in the middle. When the duty cycle is set to 2ms, the servo turns 45 degrees clockwise. When the duty cycle is set to 1ms, the servo turns 45 degrees counterclockwise. We programmed the Raspberry Pi so that it outputs the mentioned signals and rotates horn correctly. Below is the code segment we used for testing functionality.

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#yw348 Yannan Wu
#zh62 Zhengning Han

import RPi.GPIO as GPIO
import time
import numpy as np

GPIO.setmode(GPIO.BCM)
GPIO.setup(26, GPIO.OUT)
q = GPIO.PWM(26, 46.5)  #left wheel
#for i in range(0,100):
q.start(10)
time.sleep(0.1)

q.ChangeDutyCycle(5)
time.sleep(1)

GPIO.cleanup()

After we have familiarized ourselves with the functionality of the servo, we superglued the horn to the cover of the shaker can, and use the provided screw to attach the servo body to the top part of the can. By adjusting the position and angle of the cover, we are able to program the micro servos so that they rotate steadily each time, dispensing ⅛ teaspoon per rotation, as shown in Figure 4.

figure 3	figure 4

In order to integrate this design into the overall framework, we need to come up with an idea to hold the servo body fixed, because if not, the servo body will rotate instead of the can cover. At the same time, we still want the attachment between the servo and the framework to be removable, because we would like to take off the cover for refilling purposes. After a long time of trials and errors, our final solution involves firm foam blocks and velcro. We first attach the micro servo to one end of the firm foam using velcro, and attach the furring strip to the other end of the firm foam in a similar fashion. In order to attach all servos, we added three more furring strip blocks besides the three legs to hold all six shaker cans' corresponding servos. Figure 5 gives an idea of how the modified framework looks like and how the attachments were made.

figure 5

Failed Attempts

We had several failed attempts on designing this functionality, and we believe it is always beneficial to share our experience with more people to prevent others from going into the wrong direction.
        1. We tried to use DC motors with H-bridge to control the cover’s rotation, but as Figure 6 shows, the DC motor is rotating too fast, and it is very vulnerable to resistance, i.e. a small friction will cause it to get stucked. Besides, the attachment between the DC motor and the cover is not as stable, since we mainly used foam tape to glue them together. Therefore, the overall performance of DC motor is not desirable.
        2. We tried to use slotted firm foam to hold the servos instead of using velcro, but the slot became too loose to hold the servo after several rounds of rotation.

figure 6