Twitchy and Scratchy featuring the Superfluous Carnivorous Chickens
                               A CAR Production

Welcome to our 6.270 website. This site has been made for posterity so that all can remember and admire Twitchy and Scratchy, even though they are no longer with us.

 
 
The Game: CHICKEN!
 
The point of this year's contest was to build a highly intelligent cyborg chicken that could collect eggs which were strewn about the playing field. After collecting the 'eggs', the robot is to place them into the collection bins. The collection bins are actually tall plastic tubes which are placed in the playing field much in the way of pool table pockets. As balls fall in the tubes, they stack up vertically. The ball on the bottom is worth 1 point, the second ball from the bottom is worth 2 points, and so on. The tube can hold up to 8 balls, the top ball being worth 8 points.
 
The table is a 4-foot by 8-foot flat playing field which is divided in half (into two 4x4 squares) by a black line. Each of the two robots "gets" one half of the table. They start in the starting boxes at far opposite ends of the table, centered along the short side. Thus, they are facing each other from almost 8-feet apart.
 
On one long side of the table is a six-inch wide trough. This trough is seperated from the 8x8-foot part of the table by a 1/2" lip. (Balls can easily be pushed over this lip, but robots can sense the lip so that they don't drive into the trough.) There is an opening in the lib which is 12" wide at the center of the table, allowing balls and robots to get into the trough without going over the lip. Just inside this opening, the trough is flat and level with the table, but in either direction from the opening in the center of the table, the trough slants downwards. The collection tubes are at the bottom of the slopes. Thus, a ball pushed into the trough will roll down the slant and into the collection tube.
 
 
Strategy
 

We decided to have an "offensive defense" strategy. This means that we would score a point (offense), but subsequently would try to block the other robot's hole in order to prevent it from scoring.   Of the seven balls on our side of the table, one was placed between the starting block (where our robot started in a random orientation) and the trough (where you want the robots to push the balls). Because this ball was "on the way" to our robot's final destination, we simply had the robot orient toward the trough and then drive straight forward to push the ball in. This ball was almost always the first one scored, meaning it was at the bottom of the tube and earned us one point. As long as the other robot could only score one point before we blocked their tube, the round would be a double-win. If the other robot couldn't score before we blocked their tube, we would win. As it turned out in the end, the really fast robots could score two balls (3 points) before we could block their tube, but that was one of the risks of our strategy.   In order to accomplish our goals, we built a team of two cars. Scratchy (the big car) would navigate from the starting block to the opening in the trough, knocking in one ball on the way. Twichy would then be positioned to drive off Scratchy and down the ramp to block the opponent's collection tube.

 
Once the first ball was scored, Scratchy (the big car) would turn towards the center of the table and drive along the lip until he found the line that divides the table in two. This line would point him straight toward the opening in the lip. Scratchy would turn into this opening and drive forward until he sensed that he was against the back wall of the trough. This would position Twitchy on the flat part of the trough. From here, by turning on his motor in either direction, Twitchy could drive down either side of the trough.
 
 
Implementation:
...of Twitchy

Twitchy's main objective is to sail down the trough to block the opponent's hole. Twichy looks an awful lot like a skateboard and was popular with the kids. (You know, for kids!) Twitchy normally sits on a platform on the back of Scratchy, where he rides until Scratchy is positioned in the trough. Once in position (or once Scratchy thinks he is in position), Twitchy's motor turns on and he rockets off his platform and down the trough (or across the table, as the case may be). Twitchy's name comes from this part of his routine. Because all four of his wheels are driven by a single motor, he would occasionally get stuck in the tube. For instance, if he deployed slightly crooked, he would sometimes jam sort of sideways (like in Austin Powers). This was not so good. So we programed him to go forwards a little, then to stop and go back a little, etc. Like this, he would get himself unstuck if he got stuck. If he wasn't stuck, it kind of looked like he was twitching. If he deployed on the table and just kept trying to escape, it also looked quite akin to a barking guard dog being held back by a leash, which was awesome.

 
 
...of Scratchy
 

Scratchy is a whole different matter. His name is not because he scratches or anything, but just for the pun of it. (Simpsons...) Scratchy is basically a rectangular lego base with four wheels and two platforms on top. One platform holds Twitchy while the other holds the Handyboard (the "brain"). Also on top of the robot are the battery pack and Twitchy's tether. (The rules of the game state that all parts of the robot must be connected by lego at all times, so Twitchy is leashed to Scratchy with a long unrolled string of tank treads.) Scratchy is two-wheel drive, in the style of a tank. Each of the back tires can be controlled independently (with two motors driving each wheel), and the front two wheels are completely uncontrolled by motors. By powering one wheel forward and one backward, the car can spin practically in place. The gearboxes each have a ratio of 1:45. This alows the robot to drive relatively quickly but with some amount of power.

Scratchy has several sensors mounted on him as well. There are four CDS cells (light sensors) mounted on the bottom of Scratchy to allow him to orient in the starting square. These also allow him to detect the center line of the table. Additionally, Scratchy is surrounded by 8 bump sensors, two on each side. This allows him to know whenever he is touching a wall. We had some amount of trouble with this, though, because we couldn't properly mount the sensors close enough to the corners, so sometimes Scratchy would hit the walls and catch on the corner without knowing it.