Plan of Procedures

NOTE: THIS PLAN OF PROCEDURES IS COMPLETE ONLY UP TO THE BASIC STRUCTURAL PORTION OF THE PROJECT, AS PER REQUEST. THEREFORE AT THE END OF THIS REPORT ONLY THE WHEELS AND SKELETON WILL HAVE BEEN SUCCESSFULLY INSTALLED.

STRUCTURE

What it involves:

• Getting work station
• Unpacking VEX kits
• Inventory of materials
• Sorting and separating
• Creating inventory list

Explanation:

The structural subsystem of our VEX Robot will serve as our robot’s support and “skeleton.” It will hold all of the different servos and motors by partner adds into it, as well as containing other subsystems for further control.

BASICS AND PLATES

What it involves:

• Identifying parts
• Sorting by type
• Chassis bumper
• Chassis rail
• Plates
• Long bars
• Long angle bars
• Laying out on work station
• Identifying place on structure
• Sketching structure ideas

Explanation:

The very basics of the structure of the VEX Robot are made mainly from bent sheet metal with square holes (0.182” sq) arrayed on a grid-like template. The pieces are made of either aluminum or steel and they vary in both shape and size, however each piece of sheet metal is made specifically for a different robotic function.

BASIC SUBSYSTEM

What it involves:

• Identifying parts
• Sorting by type
• Fully threaded ½” beams
• Fully threaded 1” beams
• Partially threaded 2” beams
• Partially threaded 3” beams
• Pivots
• Plus gusset
• Gusset
• Steel washers
• Delrin washers
• Keps nut ¼”
• Lock nut ¼”
• Bearing block
• Bearing flat
• Square bar 12”
• Square bar 2”
• Square bar 3”
• Collar
• Threaded screw for collar
• Plastic spacer .318”
• 8-32 Screw ¼”
• 8-32 Screw 3/8”
• 8-32 Screw ½”
• 8-32 Screw ¾”
• Lock plate
• Plastic spacer .182”
• Sort pieces

Explanation:

These are the pieces which hold the VEX structure together. They use the square holes (0.182” sq) on the sheet metal plating grids for alignment and snapping in place. They allow placement components to align in necessary places, however hardware is still needed to hold them onto the structural sheet metal. The 8-32 screws and nuts attach many of the subsystem parts onto the grid. The screws come in a variety of lengths and thicknesses in order to successfully attach and mount other parts of the VEX structure.

BEGINNING STRUCTURE AND SUBSYSTEM CONSTRUCTION

What it involves:

• Allen wrenches and allen keys
• Laying out four chassis bumpers (2 long, 2 short)
• Attaching first plate (short) to longer plate to form corner
• Securing corner with (2) 8-32 Screw ¼”
• Tighten with allen key and ¼” keps nut
• Repeat until basic rectangular structure formed
• Attach plates to chassis bumpers (4 total, 2 long, 2 short)
• Secure with (2) 8-32 Screw ¼” on the (5^th) 0.182” sq hole from the side toward interior
• Repeat until rectangular structure has height
• Attach medium plate to center of structure
• Attach with (2) 8-32 Screw ¼” on each topmost furthest corner of plate
• Structure should appear as follows (overview from top)

Explanation:

At this stage, the primary and basic skeleton of the VEX robot has been constructed. It is a small, rectangular structure with a height of one sheet metal plate. This plate is attached to the bottom chassis bumpers with 8-32 ¼” screws, which are partitioned with an allotted 2 screws per sheet metal (with corresponding keps nut securing pieces) in order to affirm structural and subsystem soundness. Keps nuts were used as they have grip-like teeth which eliminate the need for a wrench. They can be replaced with Nylock nuts, which require a wrench but are able to withstand severe vibrations and rigorous movement. Regular nuts were not used as they loosen too easily over time.

To ensure that components are secure, it has been recommended that there are multiple screws for securing structural and subsystem components as that ensures proper alignment and max. strength. Care was taken to fully insert the head of the allen key into the socket as to prevent “rounding out” of nuts.

STRUCTURE VARIETY

What it involves:

• Observing what needs to be changed on our robot
• Though we do not need to do so, this would be where we modified VEX standard parts
• For example, a possibility would be to bend metal for structural modifications
• VEX parts were DESIGNED to be modified

Explanation:

Although we are not planning to modify our VEX robotics kit materials so that they cannot be re-used by future VEX students, this is the part in our process where we would do this. This could include but not be limited to bending flat plates into brackets, cutting metal components to custom lengths, and modifying various structural parts to form new configurations. This would allow structure to better suite robotics needs. However, a downfall is that it is almost impossible to form a bent piece back to its original shape, therefore this would most likely be something we would not do during our design process.

TO REMEMBER ABOUT STRUCTURE…

What it involves:

• Checking already designed and constructed portion of robot
• Evaluating strength
• Evaluating stability
• Locating  center of gravity for further construction
• Determining support polygons
• Understanding robust fabrication
• Conceptual arm extension

Explanation:

During this part of the designing process, the aforementioned and previously constructed VEX skeleton was once again brought into consideration. Before progressing on robotic construction, strength of the base was determined and considered. This involved checking the structure against overbuilding, which thankfully was not a problem with our robot. Our structure was correctly designed to integrate smoothly with the other VEX Robotics components, for example the microcontroller and other parts which fall primarily into the care of my partner, Tess. Then, the center of gravity was evaluated. This meant observing our square structure to determine the average position of all the weight on the robot. This was done with an estimation of both weight of the object and it’s position on the robot. Pieces which would be farther out, for example the claw attachment, count more towards the center of gravity calculations than centrally located parts. To find the center of gravity easy, the support polygon was assessed as per instructions from the VEX Robotics inventor’s guide. We evaluated the places where the robot would touch the ground, which were the four (4) wheels. This means that the center of gravity was directly in the center of the robot, above the place where the four wheels would meet.

For the robust fabrication considerations, we considered the most common problems with robots as described by the VEX Robotics Inventor’s Guide. It claimed that robots with pieces that fall apart or are lost easily (the fault of groups of parts not joined tightly) are usually and understandably the least stable of all the robots. Therefore a robotic part designed to more should be made with a single (1) screw to allow movement, while a part designed to remain stationary should have two (2) or more to ensure stability. Using this principle we made sure our VEX skeleton had multiple screws for stability, as we do not want the structure to move. In determining how to construct the robotic arm, bracing was also considered. Bracing is considering stresses on the robotic extensions and determining how it will lift a load. Therefore it was decided that a shorter arm would have the actual robotic scoop attached and the longer arm to support that would be braced with structural supports, all important planning processes which came after building the basic structure.

MOTION BASICS

What it involves:

• Picking the wheels; four (4) all-purpose tires
• Finding four (4) square bars (2”)
• Eight (8) collars
• Eight (8) steel washers
• Four (4) servo motors
• Eight (8) 8-32 screws (3/8”)
• Place one (1) square bar into servo motor (serve as wheel axel)
• Slide one (1) steel washer onto square bar to prevent grinding
• Slide one (1) collar onto steel bar for movement
• Side square bar through (1) square on plate extension
• Place one (1) bearing block with delrin bearings on each side of plate
• Secure one (1) servo motor with two (2) 8-32 screws (3/8”) to bearing block
• Slide one (1) steel washer onto square bar (axel)
• Slide one (1) collar onto square bar
• Slide one (1) all-purpose tire (wheel) onto square bar
• Slide one (1) collar onto square bar
• Secure three (3) collars with allen keys
• Leave some room for movement
• Repeat for three (3) remaining wheels

Explanation:

            The robotic motion subsystem in the VEX Robotics kit is used for robotic maneuverability and movement. This includes Tess’ portion of the project, the motion-generating motors, as well as my portion of the project, the wheels and gears which take the generated motion and put it into useable functions. As the VEX Inventor’s Guide states, “with the structural subsystem as the robot’s skeleton, the motion subsystem is its muscle.”

            This part of the project primarily involves attaching the wheels to the robot. This involves all the steps laid out above, which is further explained in these photographs.

Here, you can see the constructed wheel with attached servo motor. Notice the screws securing the servo motor onto the robot and the little space left for movement, as well as the two (2) bearing blocks.

Here  is more detailing on how the axel would attach to the bearing block, shown here is one side in a simplified manner. This would be the primary way to attach a wheel to a servo motor. (NOTE: Wheel is not shown.)

Here, you can see the wheel held in place by a secured collar accompanied by a washer. This square bar is too large and would not be used in our final product.

It was important to secure the bearings and keep in mind that the use of a Delrin bearing block would allow movement on our wheels, which is necessary. The steel washers were also vital as they would prevent two moving parts from grinding against each other, which would loosen the parts or damage them.

Posted in: Developmental Work