Week 8: Attaching the Servomotor Hub Horn to the Feeder Cover

The feeder cover is the only freely detachable part of the feeder once it is in use. As the only part of the feeder that will rotate freely the cover will need to be attached to the hub horn that rotates once it is fitted onto the servomotor. Initially the cover was attached to the hub horn by means of a ⅝" VELCRO Mini Fastener [1]. One half of the fastener was located on the hub horn, the other on the feeder cover. 

Figure 1. ⅝" VELCRO Mini Fasteners

However on testing the feeder it was discovered that each time the cover rotated, due to the unstable nature of the velcro, the cover experienced a "back-spin" effect. As the feeder is designed to be able to rotate to an exact amount of degrees, this was a problem. The solution was to remove the velcro attachment and attach the hub horn directly to the cover itself. Using hot glue, the hub horn was fixed at the centre of the plexiglass cover. This resulted in more accurate rotations and a more stable structure.

Figure 2. Feeder Cover/Servomotor Hub horn attachment

Week 8: Servomotor/Centre-Piece Assembly

After cutting the circular plexiglass servo support and attaching to the servo itself, it was realised that it would not create a stable enough foundation if we were to create shelf-like extrusions on the inner rounded surface of the centre piece. Another factor was that extra support would be needed to keep the servo elevated without the weight of the servo (and stand) dropping at any given moment in time.

As a result, a second structure was cut from plexiglass; a circular ring with an outer diameter that fits exactly into the inner compartment of the central PVC piece, acting as a stable "shelf". The ring's inner diameter is wide enough to fully support the servomotor stand and allow the connected servo wire to lead to the electrical compartment.

This supporting ring was fixed at a distance of __in from the upper edge of the centre piece. This distance was determined by the height of the servo. Knowing that the servo will be fixed at a certain position while the feeder cover is removed on a day to day basis, the shelf was set at a distance where once the feeder cover is replaced, the feeder is airtight and the cover would be able to rotate freely.


[INSERT PIC]

Measurements:
Inner diameter of plexiglass ring - __in
Outer diameter of plexiglass ring - __in
Distance from upper edge of PVC piece - __in

Week 8: Changing intervals

The Arduino is very beneficial for the pet feeder. The pet feeder is going to be presented in front of a panel of people. The pet feeder is meant to rotate 45 degrees every 4 hours, however, the time interval has to be accelerated in order for the judges to observe how the machine works. The fact that an Arduino is being used allows the group to simply change one line of code to change the time interval at which the top of the pet feeder rotates. The rotation will now occur every ten seconds to quickly display the use of the feeder.

However, since the actual interval is for 4 hours, the line that states 10000 milliseconds has to be changed to 14400000 milliseconds.

Week 7: Inner Compartments

This is the general shape of the compartments:

[PIC]

Limitations

There are a few limiting factors to keep in mind when designing the inner compartments:

1. The center needs to be large enough to house the mechanical/electrical workings
2. There needs to be 8 compartments for 4-days worth of food
3. The compartments need to have a minimal number of nooks for easy cleaning
4.  The design must keep in mind the limitations of the printer
• The printer prefers small pieces to larger ones
• The printer prefers a minimal amount of material used
• The printer cannot print dimensions larger than 12 inches
5. The pieces must completely separate the food compartments from the electrical components
6. The compartments housing the food must be adequately separated from its neighboring compartments.

Combating these limitations:

1 The Center

The servos is the only piece of hardware that will be in the space of the of the centerpiece.
The servo's axis of rotation is not exactly at the center:

From servocity.com

C=1.352"
L=0.174"

So the maximum distance from the centerpiece to the edge is 1.526 inches. This means that the centerpiece's interior needs to be larger than 3.052 inches

2 Eight Compartments

The compartments must allow for multiple days of convenience and care. The entirety of the container can be swept radially from the center by 360 degrees, so the mid-line of each eighth needs to be 45 degrees from the previous.

3 Easy Cleaning

A way to avoid corners made by the meeting of the floor of the container and a vertical ____ is to camber the corners. The assembled piece(s) will slope downward to achieve this effect.

[PIC]

4 Printing limitations

The lab is equipped with a few printers, each with ____ of function. The largest prints a maximum of ______ and it is preferred that the pieces being printed take under __ hours to print and that they don't use under 1 cartridge of material.

5 Separating electrical components

Week 7: Elevating the Servomotor

Now that the central piece and dividers have been made and set up within the Feeder, we need to look at positioning the servomotor so that the aluminium Hub Horn [1] of the servo aligns perfectly at the centre of the Feeder cover.

Measurements (Feeder Cover):
Diameter of plexiglass Feeder cover - 13in
Central point of Feeder cover - 6.5in
Diameter of Aluminium servomotor Hub horn -  __in

Fig 1. Aluminium Servo Hub Horn 

The Servomotor will be located within the closed-off central piece and will need to be elevated in order for the hub horn of the servomotor to be able to attach to the Feeder cover. The basic structure requires the Servo be fastened to a flat surface (circular plexiglass sheet) that will fit exactly into the central piece. This surface will need to have an opening/hole that allows the servo's control wire to lead to a separate electrical compartment (located below Feeder container). Because the hub horn is offset from the central point of the servomotor, the servomotor's position on the plexiglass surface will need to be relative to the alignment of the hub horn and the central point of the Feeder cover.

[INSERT PIC__drawn out image]

Measurements (Circular Plexiglass Sheet):
Diameter of plexiglass servomotor support surface -
Diameter of supporting plexiglass ring -
Height of Servomotor -
Height of elevated surface relative to base o the Central Piece -

Week 7: Inner Compartment Dividers

As mentioned previously, 8 food compartments will divvy up the available space to carry up up to 4 days worth of food. These compartments will be separated into equal volumes by means of 8 compartment dividers.
Based off of internal measurements, the dividers were cut to fit into the remainder of space after factoring in the central piece.

Internal measurements:
Inner diameter of Feeder container (Cake Tin) - 12in
Outer diameter of central piece (PVC pipe) - 4in
Height of Feeder container and central piece - 3in

Divider Measurements:
Length -  4 & 1/16in
Height - 3in
Thickness - 1/16in
Chamfer -

Figure 1. Plexiglass Compartment Dividers

Week 6: Drawbacks & Solutions

This week, the group was met with its first set of drawbacks. We have now reached the stage of project where the Feeder design is concrete and prototyping has officially gone underway. 

Having received the Servo Motor necessary to revolve the plexiglass feeder cover, alongside the Arduino Uno, batteries and the minor parts that complete the electronic section of the feeder, the team has begun working on the programming necessary to run the servo motor.  During the first round of testing; using a Servomotor, the Arduino Uno, and a 9V battery power source to test the rotation of the servomotor, our initial servomotor was burned out. Due to the high voltage of the 9V battery compared to the 4.8 - 6V range of the Servomotor the Servo overheated and was fried. On purchasing a new servomotor, an alternative power source was used. Instead of the 9V battery, a battery pack that consists of four AA batteries was used. This successfully ran the servomotor. In further posts, another reason for the use of the battery pack is highlighted.

The second drawback concerned the circular plexiglass Feeder cover. Due to the brittle nature of the plexiglass; on attempting to sand down the rough edges of the cover, the feeder snapped in half. A new cover was cut, adding one inch to the diameter so as to increase the coverage of the feeder.