2. Challenge The challenge of the 2007-2008 FIRST Robotics Competition game “Rack N’ Roll” was to score inflated inner tubes on posts sticking out from a rack in the middle of the field.
3. Problem Tubes could only be placed on the rack at a certain angle, or else they would fall off. The flat plate on the front of each post prevented tubes from falling off once placed, but made it harder to place them as well.
4. Solutions Design ideas included pneumatic grippers, mechanical grippers, mainly focusing on an opening and closing motion I produced an idea that used tracks of wheels above and below to “suck” in the tube.
5. My Idea The other design ideas focused around gripping the inner tube, which would usually be picked up from the floor. Tubes would be picked up horizontally, and needed to be placed vertically on the rack. The top and bottom tracks of wheels of my design would be able to be controlled independently. This would allow for the tubes to be rotated inside the gripper by running the top track and bottom track opposite each other, making picking up horizontally and placing vertically simple.
6. Prototyping The next step in our design process was to prototype ideas using basic materials. We used VEX materials to make a functioning prototype of my idea.
7. Pros Once inside the gripper, the tubes could be rotated as planned. Intake of tubes was smooth. Tubes did not change angle as they exited the gripper .
8. Cons Little contact surface area between tube and gripper. If jostled, the tube would fall and hang vertically from the gripper. VEX motors couldn’t demonstrate rotation of tubes well .
9. Next Step Prototype revisions were made Using alternative materials to contact tube Non-slip padding was attempted, but the padding would walk off of the rollers and we encountered many problems
10. Next Step (continued) Polyurethane Polycord® proved to have a high coefficient of friction on the inner tube. This thin belting would be able to run parallel with the tube, effectively keeping hold of the tube inside the gripper I made a prototype using this material along with a PVC plastic skeleton frame.
11. Power Car window motors were chosen to power polycord belts. Tubes could be precisely angled inside this new gripper Not easily moved Polycord proved to be best material to contact tube
12. Final Prototype This design was chosen by the team to be implemented into our final robot design.
13. Evolution A welded aluminum version of my design came next Lightweight Robust We had full control of a tube that was in our possession, and could perfectly adjust angle to place on the rack.
14. Controls Joystick control of gripper Up and Down on joystick picked up and shot out tubes Left and Right on joystick rotated the tube inside the gripper
15. Positioning of the Tube The prime position for rotation of the tube was in the direct center of the gripper Problem: Difficult for driver to determine exactly where tube sat in gripper during game play.
16. Solution A VEX bump sensor was added to very back of the gripper Program was written to override operator controls for a fraction of a second when bump sensor was touched (when tube was fully sucked in) The tube was backed out approximately two inches during this time to position it back in the center of the gripper
