MIT 6.270 Competition - Team 41

"Stucco"


Overview

6.270 is an entirely student-run class during IAP in which teams of two or three build autonomous robots to compete in a contest. The robots must be built entirely out of Lego and be able to comptete in a specific contest which changes each year. This year the contest was "Chicken." The basic goal of Chicken was to move balls from the playing area into a trough, thus scoring points. For more information about 6.270 or the specifics of this year's contest, visit the official 6.270 website.

The Team

We are David Reinharth and Seth Tardiff, both Juniors at MIT. Dave is Course 3 (Materials Science) and Seth is Course 6 (Computer Science). We're both Brothers in Sigma Nu at MIT. We worked pretty well together during 6.270 mostly because we have known each other for a few years now and are both easy-going enough to make compromises when they're necessary.

Strategy

During the design phase, we had one main goal in mind: simplicity. This mantra carried over to our choice of strategy, as we decided to build a robot which could essentially perform only one or two basic functions, but could perform them consistently well. The most simple and yet effective strategy that we could think of was to knock a single ball into the scoring trough and then proceed to block the scoring hole of the other team. Ideally, this strategy would allow us to only be defeated by robots that could successfully score two balls in the time that it took us to score one and block their hole. This seemed like an unlikely case, given the extra amount of time it would require for any robot to score two balls.

In more specific terms, our strategy consisted of these steps:

  1. Orient the robot based on the board colorations and face the trough.
  2. Drive straight towards the trough, knocking the ball into the hole along the way.
  3. Extend the front of the robot over the trough and deploy a separate (yet tethered) car which drives down the trough and blocks the opposite hole.
  4. Wait until the sixty seconds of the contest have ended.

Mechanics

The mechanics of our robot can be broken down into a few subsections: the drivetrain, the sensors, the car, the car platform, and the ramps. Each part deserves some discussion.

  • The drivetrain consists of two motors powering two wheels (one each) using a 45:1 gear ratios. Each motor and corresponding wheel is independently powered, allowing for a variety of turning styles and a great deal of mobility. The two wheels (and the majority of the robot's mass) are in the rear part of the robot. The front of the robot slides on a single point, a curved piece of Lego.
  • There are a total of seven sensors on our robot (keeping with the belief that simple is best). Three of the sensors are infrared photosensors placed under the robot to allow for the initial orientation based on the board coloration. Each of these three sensors is accompanied by an infrared LED to provide a consistent light source for the sensor. Another sensor is a switch sensor placed under the front section of the robot to detect when the robot has reached its desired orientation over the trough. Two more sensors are used inside the gearboxes to provide shaft-encoding functionality. These two breakbeam sensors are placed on the second gear of each gearbox allowing for very accurate measurements of how far each wheel has progressed. By tracking the progress of each wheel individually, the robot is able to achieve consistent turns and straight driving. The final sensor is a CDS photosensing cell which senses the start light in the table and tells the robot when to begin moving.
  • The car is a four-wheeled Lego structure that is driven by a single motor connected to two drive wheels. The two drive wheels are located at the center of the car while the others are located at the ends (one centered at each end). The car is connected to the main robot by a tether made of short strips of Lego connected in an accordian-like manner. This tether is designed to fold and rest above the car, unravelling as the car deploys down the trough.
  • The car platform takes up the entire front section of the robot and is simply a flat area on which the car rests until it is deployed.
  • The ramps are located on the sides of the car platform and are designed to be lowered into the trough and driven over by the car. Only one ramp deploys in any given round of the contest (which one depends on which side of the board the robot starts on). The ramps are lowered using servo motors, one on each side of the robot.
The photos below show the robot in various orientations.

Final stats:

  • Length: 12 inches
  • Width when closed: 10.5 inches
  • Width when both ramps extended: 30 inches
  • Motors: 5 total - 2 servo, 3 regular
  • Main gearboxes: 6 gears in each box providing 45:1 ratio
  • Car gearbox: 3 gears providing 15:1 ratio
  • Sensors: 7 total - 3 infrared photosensors, 2 breakbeam, 1 bump switch, 1 CDS cell
  • Processor: Handy Board with 6.270 expansion board attached
  • Memory: 32k
  • Power: 3 Hawker (2.5 volt) batteries in series for motors, Handy Board internal 9 volt battery for processor

Results

Our robot succeeded in several ways and failed in one important other. The successes included having very consistent orientation and drivetrain systems which allowed us to easily maneuver the robot. The ramp and car systems also worked well. The biggest recurring problem was our robot's inability to consistently get itself into proper position above the trough so the car could be deployed... this would prove to be our downfall.

In the first round of the contest, we easily qualified and earned a double win with a 1-1 tie. The other robot scored a quick point and nothing more.

The second round was a dissappointment, as a simple human error cost us the win. When placing the robot on the board, we misaligned it slightly, causing it to be unable to complete the ninety degree turn to face the trough that was necessary. The robot got stuck against the obstacle on the board and could never recover. Despite losing this match, we proceeded to the final competition with a 1-1 record.

The final competition started out well as we won our first match with a double (1-1) win. The next round would be our last, however, as our car failed to deploy properly and the other robot successfully scored two balls. This glitch was caused by a "hop" that caused our switch sensor to prematurely trip and deploy the car before the robot was totally over the trough. The car deployed and scurried across the contest table in a somewhat entertaining, yet wholly ineffective, manner.

After losing for the second time, we were eliminated from the contest. We finished in about 20-25th place out of 60.

Photos

For more and larger photos, click here.


Figure 1: The final version

 


Figure 2: The robot with one ramp lowered

 


Figure 3: After the car has been deployed

 


Figure 4: The car

 


Figure 5: An early prototype

 


Figure 6: Dave working on the robot