Team Seven/Final Paper
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These problems were actually resolved when we had to switch to rubber wheels and slower, more powerful motors in order to properly drive on the gym tiles. During the switch, we noticed that while our original motors looked the same, they were actually different models, thus explaining the speed disparity. The switch allowed us to drive much more effectively, and gave us a much smoother drive system than we had before, though we had to give up the ability to use encoders in the way that we planned, since these wheels did not have the required holes (though we found that we didn't really have the time to incorporate encoder information well anyway by this point). These motors didn't have to draw quite as much current, so we were able to get away with not using a separate motor control board and still managed to drive without burning any of our electronics out. | These problems were actually resolved when we had to switch to rubber wheels and slower, more powerful motors in order to properly drive on the gym tiles. During the switch, we noticed that while our original motors looked the same, they were actually different models, thus explaining the speed disparity. The switch allowed us to drive much more effectively, and gave us a much smoother drive system than we had before, though we had to give up the ability to use encoders in the way that we planned, since these wheels did not have the required holes (though we found that we didn't really have the time to incorporate encoder information well anyway by this point). These motors didn't have to draw quite as much current, so we were able to get away with not using a separate motor control board and still managed to drive without burning any of our electronics out. | ||
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Revision as of 05:41, 3 February 2013
Contents |
Overall Strategy
Team 7's strategy went through three primary phases that depended fairly heavily on our mechanical capabilities. For most of MASLab, we intended to play a low-ball-count high-ball-value game where we would not bother going after the ball release button and put as many balls as possible into the top tower. After a while, we realized that this would not be optimal if we were collecting balls thrown over from the other side, so we designed a two-hopper system that could differentiate ball colors so that we could put only our balls in the tower and throw the rest back over the scoring wall. Unfortunately, this strategy had to be simplified a great deal when the competition arrived, because we didn't have the time to implement the required systems. As such, we found that we could maximize our points by scoring over the wall, in which case which color balls we collected wouldn't matter, because gaining 20 points and causing the opponent to lose 20 points had the same net result. In the end, our strategy boiled down to getting any ball we could for the first 150 seconds, and then spending the last 30 seconds looking for the yellow scoring wall and attempting to score with all the collected balls.
Mechanical Design
Our final mechanical design used a two-level system with a ball collector on the bottom and a hopper/dispenser on the top, each powered by a rubber band roller. An Archimedes screw was used to transfer the balls from the collection area to the hopper, and all of this was mounted on a two-wheeled drive system with a ball transfer unit in the back to provide balance.
Ball Collection
Storage Areas
Archimedes Screw
Rollers
Drive System
For much of IAP, the robot had a drive system comprising of two small, fast motors with thin, water-jetted aluminum wheels. These wheels were made to have sharp spikes to provide traction on the carpet, and had 20 openings along them to allow for the use of optical encoders. The drive system was mounted onto the frame using aluminum L-brackets, and was placed just underneath the aluminum bottom of the robot's collection level. However, when the type of floor used for the competition changed from carpet to gym tiles, we had to drastically change the way we approached the drive system. The metal wheels dug into the mats and the motors we had didn't have enough power to move the robot effectively on this surface.
During this period, we also experienced issues relating to an imbalance in the speeds of the motors. We found that one side drove much faster than the other, and had to do a significant amount of compensation- giving the faster side speed commands that were 20% slower and the slower side commands that were 30% faster than the actual baseline input value in order for the robot to approximately drive straight. In the process of testing this drive system, we had at least two motors destroy their internal gearboxes, wearing the gears down until the device was essentially useless. We also had a few incidents where the amount of current that the drive system was drawing overwhelmed our motor control board, causing it to fry. At least one incident involved a very visible fire on the side of the robot.
These problems were actually resolved when we had to switch to rubber wheels and slower, more powerful motors in order to properly drive on the gym tiles. During the switch, we noticed that while our original motors looked the same, they were actually different models, thus explaining the speed disparity. The switch allowed us to drive much more effectively, and gave us a much smoother drive system than we had before, though we had to give up the ability to use encoders in the way that we planned, since these wheels did not have the required holes (though we found that we didn't really have the time to incorporate encoder information well anyway by this point). These motors didn't have to draw quite as much current, so we were able to get away with not using a separate motor control board and still managed to drive without burning any of our electronics out.
