2003 Spring - Watermelon Drop

Every year on UC San Diego campus, Revelle students select a watermelon queen, who drops a watermelon off of Urey Hall. The origins of this contest go back to a physics final where one of the questions related to how far a watermelon will splat after it has been dropped form Urey Hall (the initial velocity of the watermelon, height of the building, number of watermelon pieces, and momentum of some of the pieces were provided). After the final, a number of students went up to Urey Hall to verify their analytical results (a key process of applying analysis to design!). The first Watermelon Drop was in the Spring of 1965, and it has been repeated every year since then as the first tradition of UCSD. Each year the distance of splat recorded in an attempt to break the record.

In this quarters MAE3 design contest, student teams will build robots based upon the theme of the Watermelon drop. The contest table is shown below. In the center of the table is a watermelon, and on each side of the tables is a watermelon rind with seeds inside of it. This watermelon happens to have posts that protrude on both sides. The goal of the contest is place as many seeds as possible onto the watermelon posts (this is in an effort to stuff the watermelon with additional seeds, hoping that one will contribute to an eventual record breaking splat). Each teams robot must start within the designated starting area on either end of the table.

Contest Table

Rind Watermellon Seed Loader

Watermellon

The object is to get as many seeds from the rind on to the watermelon. Click to see demo.

Close up of Rinds. 15 seeds will fill each rind

Close up of Starting Area. Block will be bolted to table and will always be in starting area. There will be a 4” high area inside the block, and eight threaded holes on the top of the block. The starting area is 12”x12”x16.5” high, but the total size of the machine is limited to 12”x12”x12”.

There will be a central cable going from the top of the watermelon to the top of the table

Scoring is as follows:

o One point is awarded for each seed that is placed onto the watermelon posts on the starting side of the table

o One point is awarded for each tie breaker that ends up on the starting side of the table

o Two points are awarded for each tie breaker placed onto a watermelon post

o In the event of a tie, the team with the most tie breaker points will win

Each MAE3 design team will build a robot that will compete head-to-head on the contest table. The robots will be arbitrarily assigned to start in either the right or left starting regions. The goal of the contest is to place as many seeds into the watermelon during a 60 seconds playing period. Each team will receive points for seeds placed into their starting side of the table.

The contest will involve a head-to-head competition between two design teams (each consisting of 3-4 students). Each team will build a robotic machine that is electrically controlled with switch pads. The starting size of each machine is limited to a cube of 12”x12”x12” and must fit unconstrained (i.e. not touching the sides) of the test cube. Teams will be assigned randomly to start in either starting area A or B. There will be three playing fields built to accommodate all students in the class, and manufacturing tolerances will results in small variations between the contest tables. It is the design teams responsibility to develop a robot that will work on all contest tables.

Each team will build a machine using the kit parts described below to perform the task. The kit will include 5 DC motors (2 will have gearboxes) and one solenoid. Electrical power will be provided from a constant voltage power supply with 5VDC output, and can be controlled with two switch boxes (each switch box can be controlled by a different team member). Each switch box has two Double Pole Double Throw (DPDT) switches (these switches can operate a DC motor in either direction). Note the kit contains five DC motors and one solenoid, but only four user controlled switches. In order to operate more than four motors independently one must use contact switches on the machine. Use of motors, solenoids, and switches will be covered in lecture and is described in the Mechanical Device textbook.

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Contest Event Description

The contest will be held during the MAE finals period and will be open to the public. The contest will be held in a single elimination fashion (like a tennis tournament). During the lab period of the last week of classes, each section will hold a section-wide contest. The results of this contest will be used to seed the placement of the final contest. Thus teams that perform better during their section contest will have statistically easier contests in the early rounds. Since the number of teams in the class will not be exactly a power of 2, the higher seeded teams may get a "buy" during the first round. If necessary random numbers will be used to ensure a proper contest pyramid.

A trophy will be presented to each member of the winning teams, and a number of machines will be selected for display in the Design Studio and MAE Department. Team members must work out among themselves who will keep the final machine (after their display period). All members will make a web page describing their machine (including video), which they can cherish forever.

Each team must return the geared motors, since their price is not included in the course fee. Anyone wishing to keep their complete robot can purchase replacement geared motors, and turn them in to keep their robot.

Contest Rules

Energy Sources: The energy used by the devices in the competition must come solely from:

Potential energy derived through a change in altitude of the center of gravity of the machine;
Potential energy achieved by the deformation of the springs provided by the Kit
Electrical energy derived through the umbilical during the 60 seconds when the power supply is energized.

Size: At the start of each competition, every part of the machine must fit, unconstrained, inside the 12”x12”x12” starting area, whose base is completely aligned with the marked starting area on the playing field.

Umbilical Cables: The electrical connections will made to a single umbilical cord hung from above the table; one on each side of the table. The umbilical cord cannot be touched during the contest, and there will be some drag from the cable. Each machine must be designed to overcome this drag if necessary for motion of the machine.

Detailed Rules

Judges and/or instructors will disqualify any device that appears to be a safety hazard.
Any machine that has flying parts must notify opponents, and all contestants must wear safety glasses during the machine operation.
If a projectile is used, for reasons of safety, it must have a frontal area greater than 2 inch squared.
Contestants will randomly be assigned to start on either side of the playing field.
A maximum set-up time of 2 minutes will be allowed at the contest table.
A maximum of 1 minute will be allowed for removal of all parts of each machine after each contest.
Operators may interact with their machine during a contest only through normal operation of the switch boxes (for example you cannot touch the machine with one's hands during operation).
It is allowable to adjust the configuration of the machine between contests; for example adjusting the configuration to the side of the playing field the machine starts on.
Each machine can only interact with the surface of the playing field and objects on the playing field.
The judges will wait until all the seeds have stopped moving before determining the winner.
A seed will be considered ‘ON’ the watermelon if it’s circumference goes around a watermelon shaft, and the center of the location is within the vertical projection onto the length of the shaft.
Points will be awarded based upon the final location of the seeds, regardless of which machine moved the seeds.
A seed will be declared out-of-bounds if it is off the playing field.
The tie breaker must be on the playing field for it to count.
Damaging the playing field, the watermelon, rind, seeds, or the control boxes may result in disqualification.
Purposefully using the electrical cables for any purpose other than transmitting electrical is not allowed.
Gaining traction by use of adhesives, or by abrading or breaking the surface of the playing field is not allowed.
A machine may not contaminate with lubricant or other substance the playing field, an opponent's machine, or the playing field (internal lubrication of a machine is permissible).
Kit materials may not be changed chemically. DC Motors may not be rewound.
The paper that is attached to the acrylic in the kit cannot be used as a separate element in the machine. If any piece of paper is detached (even partially) from the acrylic it must be discarded.
The insulation must remain on the electrical wire in the kit except where the wire end is attached to another component, and there up to 0.5” of insulating can be removed.
The clear acrylic 0.25 thick is for testing. If you include any of this acrylic in your final machine, you must remove an equivalent amount of colored acrylic that was used in making the part.
Spare parts are available on a limited basis. Students should go to the tutors of their section to receive replacements for parts broken. Student can purchase replacement acrylic from upper campus machine shop or off campus (see Chris Cassidy for sources)
Machines may be designed to interact. However, it is not in the spirit of the competition to intentionally damage another machine and no part of the kit may be used in a manner that is intended to cause harm. Any device which is designed to chop, break, or penetrate another machine will not be allowed to compete. If you think your machine may be at risk for violating this rule, ask early before you build it!
Machine advertisements and decorations much be of the nature that it does not offend any other students or audience participants (use common sense!).
All rulings of the judges will be final.

Any modifications or clarifications to the rules or kits will be posted on the class web page.

Clarification to Contest Rules

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Kit Parts Rules

Each machine must be constructed solely from materials provided in the Kit listed below, i.e. one cannot substitute a 12"x16" piece of acrylic with a 6"x32" piece.

If a part of the kit is damaged it can be replaced from the scrap pile, as long as the design team can show that they could completely rebuild their machine solely from the kit.

In addition to the kit parts listed in the table, the following items may be included in the machine:

· Nuts, bolts, and washers included in the Design Studio bin. These include bolts from size 2 to size 10, and metric screws for mounting the motors.

Only take nuts and bolts from the bin as you need them, and search through the spare bolt bin before taking more (we went through $1,500 in fasteners last year!)

· Fasteners can be used only for fastening purposes, and thus must fasten at least two other parts together.

· Adhesives; including hot melt glue, and acrylic adhesive.

· Tape used ONLY for electrical insulation

· Lubricants used only to reduce friction.

· Nonfunctional decorations.

Replacement Material Policy

We have some extra material that can be used for experimentation. This material will be made available in the lab scrap bins. In addition each section tutor has access to a limited amount of replacement material for their section. If you need replacement parts, contact your tutor. Some replacement of "mistakes" made to kit parts will be available, but supplies are limited, and replacement is not guaranteed.

Kit Part List and Motor CAD Models

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Frequently Asked Questions (FAQ)

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