We built our game piece manipulator out of acrylic plastic and High Density, High Molecular Weight Polyethylene. It looked awesome since you could see the entire gear train in motion but it only lasted about 15 minutes once in use. The sheet plastic just shattered into little pieces. Fortunately we have time to remake it out of aluminum.
The aluminum manipulator is straining the arm servos. We sacrificed gear ratio or torque for range of motion on the lifting arm. Since servos only travel a limited amount before they hit their own internal stops, having a great gear ratio meant that the arm traveled less of an arc than the servo rotation. Finding the right trade-off between arc traveled and lifting capacity was the key. Since we were out of parts, money and time, we punted by adding rubber bands to lessen the load at the bottom of the arm travel, when it is picking up the block. Adding a hard stop to the arm to prevent overtravel of the arm ended up providing a bonus in the way of a pivot point on the rubber band. So the stretch and retraction of the rubber band is now a compound action. As the arm is lowered, the stop forces the rubber to stretch around it, adding tension at the end where it was really needed.
Today we traveled to IIT to attend the first Qualifying Tournament of the season. We went to gain more knowledge of the game and the competition environment and also to volunteer where needed. We were also hoping to have some time on the practice field, so we brought the robot along.
IIT had three competition rings and one practice ring. The pit area was huge, stretching around the building in an hallway around the perimeter of the building. The rings had elevated cameras televising the competition on overhead projection screens. We really liked this since the field often has a lot of judges, volunteers, photographers and the announcers standing around it. If you are in the audience, you are always looking around the people in front of the rings. This makes it difficult to see the action in the ring, but the overhead cameras have an unfettered view.
IIT also provided an overflow room for viewing the matches. It was a little quieter in that room and you could really sit close to the screen making the competitions, literally, bigger than life.
Our robot had plenty of time on the mat in the practice ring. We made quite a few program changes and outlined some improvements in the hardware. Tetrix doesn't provide a way of adjusting gear back-lash since all the holes are drilled on a fixed spacing. We find that the slop in the axles and bushings is enough to provide insufficient gear tooth contact and slippage of the gears at times. Something to think about.
We enjoyed the competitions and came away with greater understanding of the game along with quite a few new ideas on strategy. Interviewing the other Teams was a lot of fun. Everyone was very gracious!
We spent some time looking at the poster boards, business plans and finding out about the non competition awards.