Engineering Systems Technical Paper

Six Weeks Engineering Project Proposal

Goal of Project

To build a robot to compete in the 2007 FIRST Robotics Competition

Research

I. Background Information

FIRST (For Inspiration and Recognition of Science and Technology) was founded in 1992 by inventor Dean Kamen as a way for students to get directly involved in engineering, science and technology. Based on a sports model, FIRST is aimed at changing the culture of America to one that embraces science and scientists rather than actors and athletes. With the aid of MIT Professor Woodie Flowers, Kamen developed a sports-like competition for high school students around the country. The first competition, Maize Craze, was held in a New Hampshire gymnasium, and 28 teams competed with 11 kg robots. Today, more than 1300 teams from several countries, on 5 continents, compete at nearly 40 regional competitions in North America, Brazil and Israel.

The 2007 FRC game is titled Rack Ð''N Roll and involved manipulating inner tubes and placing them on a large "rack" structure, with 24 PVC "spider legs" sticking out. Additionally, teams may score points by raising robots at the end of a match. The game is played between two, three team "alliances", and consists of a 15 second autonomous period followed by 2 minutes of driver control.

II. Principle of Operations

Sub-systems:

*Mobility

-Function:

-Move robot around field via two sets of motors, reduced through a gearbox, and chained to wheels

-CIMs move at ~4320 rpm under load, which is reduced by 10.67:1 in low gear, and 4.17:1 in high gear, then further reduced by a 2.5:1 sprocket reduction. With 6" wheels, top speed in high gear is ~ 10 fps in high gear, and ~4 fps in low gear.

-Gears are shifted in a "dog style". Two different sets of gears (with different ratios) free spin on the output shaft. A dog gear sits in between them, and spins with the shaft. A piston actuates the dog, engaging it with one of the two sets of gears, causing the output shaft to spin at the resulting speed of that reduction.

-Components: (see attached BoM)

*Arm/Manipulator

-Function:

- Acquire tubes from floor and place on rack through pneumatic claw, pneumatic wrist, and dual-globe motor powered shoulder joint

-The two globe motors have 15 tooth pinion gears that meet a 72 tooth gear mounted to the arm, resulting in a 4.8:1 reduction. Given that the arm only needs to move about 120 degrees, the arm takes ~1.1 seconds to travel from the floor to its highest position (under full power, which was rarely used).

-The arm consists of two sets of aluminum square channel, one resting inside the other. Before a match starts, the smaller tube is retracted fully (until the wrist joint touched the outer channel). A small eye-bolt is tucked behind a structural member in the shoulder that holds the arm in the retracted position. When the arm is raised, surgical tubing attached to the eye-bolt pulls the inner tubing out, and the eye-bolt locks in a mechanism at full extension.

-Components: (see attached BoM)

*Controls:

-Functions:

-When the drivers move a joystick (or flip a switch, etc.), the operator interface sends a signal to the robot controller via the radio modems. The controller then evaluates that signal and based on the code, sends out various commands to the victor 884 speed controllers, spike relays, and servos. The victors send varying amounts of voltage to the motors, controlling the speeds they spin at. The spikes (which we only used to actuate the pneumatics) do not limit voltage, only sending positive or negative (neutral as well?) signals.

-All the victors, spikes, motors, and solenoids were attached to each other by Powerwerx Power Poles connectors, allow for quick disconnects. All the sensors went through a single DB25 connector. The whole control box could be removed with 7 disconnections, in less than 30 seconds.

-Components: (see attached BoM)

Technical Requirements

I. Requirements

1. Meet all 2007 FRC rules (4', 120 lb. class)

2. Be able to drive when instructed to by the operators

3. Be able to score tubes on the rack

4. Be able to drive up 30+ degree incline (other robots ramps)

II. Constraints

1. six week build period

2. 38"x28"x48"