Status: Archived
Time: 2013-2014 Winter
Completion Level: Complete
Description/Goal:
This was a small (<30cmx30cmx30cm) robot designed to compete in the Scioly division B event: Robocross. Your score was calculated based on each piece (ping pong balls, lego’s, batteries, etc) moved into the various quadrants of the field, with multipliers for being in an upright jug. My robot was designed to easily achieve a perfect score within the 3 minute time limit, and win by the tiebreaker: fastest time. A video of a practice run for our final robot is below:
[youtube https://www.youtube.com/watch?v=Qz9cXYQ2z1M]
Solution:
Version 1: Old non-programmable vex platform.
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This first attempt was severely limited by the inability of the sheet metal scoop to get under the lego bricks, as well as the slow process of raising the scoop. We used it throughout the invitational season so we could develop our second robot without worrying about keeping it secret or having to rush versions.
Version 2: Modern vex cortex programmed in robotc.
For the second iteration, we explored more innovative solutions to the problem. My driver Rakesh Ravi was unhappy with the time required to dump each scoop of items, so we searched for a way to have the jug held on the back and quickly ferry the items into it. We landed on a sticky belt with a scraper on the back, so the driver would only have to push the belt up to the the item and the robot would lift it into the jug.
Obviously, this was more complicated than expected. The first iteration of the belt utilized transfer paper for book sealing, which was too weak to firmly hold the tennis ball. Gorilla tape on the other hand was too strong and would not release the batteries, jamming the belt. After trying every possible combination of duct, masking, packing, and adhesive coated tapes, I ended up choosing to apply gorilla tape, with transfer tape over most of the belt except for a small chunk to grab the tennis ball.
The next issue was grabbing the jug. We needed some sort of arm that could pick it up and hold on to it firmly for the rest of the run. I settled on a dual-jointed arm with potentiometers for position feedback and a control loop that was based on a set of known positions that the arm would “snap” to at the press of a button. This meant in the match the driver only had to approach the jug and in three button presses the jug was firmly clamped to the robot.
We used an omnidirectional drive platform for easy repositioning, and once the driver became used to it we saw a huge increase in speed. This robot was programmed in robotc, and featured a complex but very efficient controller layout view-able below:
This robot could easily get a perfect score in under half the time limit, and occasionally saw times under 1 minute. In the national competition, we had a somewhat unlucky run mostly due to the immense pressure to perform, and got a 1:50 run securing a top 15 (11?) position.