First Robotics Manipulator DesignPresentation Transcript
Brad Mello FIRST “Rack N’ Roll” Manipulator Design
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.
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.
Design ideas included pinching mechanisms and pneumatic grippers
Many were flawed early on
My design would allow tubes to be oriented at any angle
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.
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.
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 .
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 .
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
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.
Power Car window motors were chosen to power polycord belts. Tubes could be precisely angled inside this new gripper Difficult to knock free Polycord was able to compress as tubes were brought in
Final Prototype This design was chosen by the team to be implemented into our final robot design.
A welded aluminum version of my design came next
A tube was able to slightly compress the polycord
Added friction between tube and gripper
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
Benefits to Playing Style The best way to score on the rack was to have the tube at a 45 degree angle. This angle was best to avoid to small rubber house sticking The manipulator was able to rotate the tube to this angle no matter the position of the rest of the arm.
Playing Style (continued) Tubes could be scored at any of the three different post heights, and our gripper was able to adjust the angle of the tubes effectively at all three of these heights.
Positioning of the Tube The prime position for rotation of the tube was in the direct center of the gripper Problem: Difficult for drivers to determine exactly where tube sat in gripper during game play.
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
Predictions about game play were correct
Most tubes were picked up from ground level
Angle of tubes needed to be adjusted often and with haste
Review This is a video demonstrating our robot rotating an inner tube inside of its gripper. Click image to play video