Dunking Arm
Hopper
After striking the BRB, the balls were placed by hand in a cardboard hopper mounted on the very top of the robot. Initial designs called for the construction material to be 1/8" Duron, but analysis soon showed that a lighter material would just as well suffice (since the hopper itself supported no significant weight aside from the Nerf balls). The hopper joined via a central axis of 1/4" aluminum and two small bearings to a cardboard support, which ran the length of the hopper base and itself joined to the four support rods with the same kind of shaft.
The nature of the dunk itself lay in a piece of string, that ran from the hopper base to the front of the hopper itself. After the dunk mechanism had raised the hopper a certain distance, the string would be tightened and the hopper thus forced forward into a steep angle from its stable, flat position.
After striking the BRB, the balls were placed by hand in a cardboard hopper mounted on the very top of the robot. Initial designs called for the construction material to be 1/8" Duron, but analysis soon showed that a lighter material would just as well suffice (since the hopper itself supported no significant weight aside from the Nerf balls). The hopper joined via a central axis of 1/4" aluminum and two small bearings to a cardboard support, which ran the length of the hopper base and itself joined to the four support rods with the same kind of shaft.
The nature of the dunk itself lay in a piece of string, that ran from the hopper base to the front of the hopper itself. After the dunk mechanism had raised the hopper a certain distance, the string would be tightened and the hopper thus forced forward into a steep angle from its stable, flat position.
Support Rods
The beauty of the dunk mechanism lay in the four 8"-long support rods, which ran from the hopper base to the hopper support structure. Using two forward and two aft rods separate by precisely 2.5", the hopper and support remained at the same level as the rods raised them into the air. One of the rods had a 90-degree dogleg below the 8"-mark and a 6"-extension protrude out from the curve, at the end of which a rubber band joined to the stepper motor. This provided the lift for the dunk; as the motor tightened the rubber band, the dunk mechanism was raised. The 6" provided a mechanical advantage for the dunk, meaning that a relatively small amount of torque could be exerted by the motor and still smoothly lift the dunk arms. (See Note: Mechanical Advantage).
The rods themselves joined to the base at eight points via six different couplings. Small bearings were sunken into the ends of each rod, through which a small piece of 1/4" aluminum shaft was run. In this way the rods were allowed great freedom of movement without too much friction interfering; since the stable position of the dunk hopper was relatively flat, too much instability during the dunking could have caused the balls to roll from the hopper.
The beauty of the dunk mechanism lay in the four 8"-long support rods, which ran from the hopper base to the hopper support structure. Using two forward and two aft rods separate by precisely 2.5", the hopper and support remained at the same level as the rods raised them into the air. One of the rods had a 90-degree dogleg below the 8"-mark and a 6"-extension protrude out from the curve, at the end of which a rubber band joined to the stepper motor. This provided the lift for the dunk; as the motor tightened the rubber band, the dunk mechanism was raised. The 6" provided a mechanical advantage for the dunk, meaning that a relatively small amount of torque could be exerted by the motor and still smoothly lift the dunk arms. (See Note: Mechanical Advantage).
The rods themselves joined to the base at eight points via six different couplings. Small bearings were sunken into the ends of each rod, through which a small piece of 1/4" aluminum shaft was run. In this way the rods were allowed great freedom of movement without too much friction interfering; since the stable position of the dunk hopper was relatively flat, too much instability during the dunking could have caused the balls to roll from the hopper.
Dunk Base
The mounting part of the dunk mechanism was the dunk base. Made of 1/8" Duron, it both provided a place for the support rods to mount (as seen by the eight rectangles in the base itself) and was large enough to allow flexibility in joining the dunk module to the rest of the robot. Because of its large size, the motor could be very easily mounted to the base via more 5/16" threaded rods, which meant that the dunk as a stand-alone module could be separated from the robot for test purposes and then easily re-attached later for a complete system.
The stepper motor used to power the dunk mechanism provided ample places for mounting, and so could be drilled directly through and attached to the rest of the dunk module via corner braces and threaded rods . A rubber band was used rather than a string to convey tension from the motor shaft to the doglegged support rod to prevent any sudden ramp in torque once the length of the string was reached, and a second string attached from the edge of the hopper support to the hopper to limit the dunk motion.
The mounting part of the dunk mechanism was the dunk base. Made of 1/8" Duron, it both provided a place for the support rods to mount (as seen by the eight rectangles in the base itself) and was large enough to allow flexibility in joining the dunk module to the rest of the robot. Because of its large size, the motor could be very easily mounted to the base via more 5/16" threaded rods, which meant that the dunk as a stand-alone module could be separated from the robot for test purposes and then easily re-attached later for a complete system.
The stepper motor used to power the dunk mechanism provided ample places for mounting, and so could be drilled directly through and attached to the rest of the dunk module via corner braces and threaded rods . A rubber band was used rather than a string to convey tension from the motor shaft to the doglegged support rod to prevent any sudden ramp in torque once the length of the string was reached, and a second string attached from the edge of the hopper support to the hopper to limit the dunk motion.
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