The Gripper
The can gripper was the most important aspect of our overall design. The kwy design criterion for our gripper was to be able to operate the gripper with only a single servo motor. That is, we wanted to both close the jaws and raise the can in a single motion of the motor. We began this process by trying a couple cam designs and linear motion ideas. Although possible, these types of grippers did not give us the performance flexibility we desired. Therefore, we switched to a rotational motion for the gripper. Upon this switch, we determined it was necessary to attach to strings to the robot from up on the Ladar mounts which would pull the jaws open once the strings were placed in tension. Additionally, a spring was placed on the bottom of the jaws in order to keep the jaws closed whenever the strings were not under tension.

With these stings in place, a downward motion by the servo motor would lower the closed jaws up until the point that the strings became taught. Upon placing the strings in tension, the strings would pull back on the jaw mechanism forcing the jaws open, overcoming the force of the spring at the bottom of the jaw mechanism. The lower the position of the servo motor, the wider the jaws opened, creating an large opening with which to grab the can. Similarly, as the jaws were raised, the tension in the strings decreased, allowing the force of the spring at the bottom of the jaws to overcome the tension and close on the can. After the jaws closed on the can, the strings on the gripper would become slack and the can could be effectively raised off the ground. With this design, we were able to pick up the can with absolute confidence and achieve our goal of using only a single servo motor. Please see the pictures and videos to gain a better understanding of our gripper mechanism.

The Ball Collector
Having successfully designed a gripper using a single servo motor, we were provided the luxury of implementing two servo motors for our ball collection device. We believed that the ability to use two servo motors in our ball collection mechanism would provide us with a significant advantage in terms of collecting golf balls and separating them by color. Additionally, we wanted a ball collection device which would be capable of simultaneously depositing both the blue and orange golf balls. However, the mounting of our gripper forced us to mount the ball collection mechanism on either side of the gripper such that we were able to collect golf balls while holding the can. This forced our robot to be quite wide in the front.

The actual mechanism was composed of two separate containers each capable of holding three golf balls. These containers were long, narrow channels which sloped out from the under the center of the robot at about 45 degrees to a position just to either side of the gripper. Each channel was equipped with a rotating gate which would open and close as balls were to be collected. Additionally, a stopper was placed on the back of the gate such that when it was fully opened, the balls would not be capable of escaping from the containers.

In operation, the robot would first find a ball based on its HSV colors. Upon finding a ball, the robot would make a quick motion backward and then forward to force the golf balls already collected to the back of the container to make sure they would be blocked by the stopper when the gates were opened. Note, the gates were opened so that the blockers were in place as the robot moved forward in this process. The robot then proceeded to align the position of the ball to a set location just in front of the container. Once aligned, the robot moved forward and the gates were closed slightly such that the balls could enter the container and make it past the blocker. As soon as the ball entered the container, the gates were closed to trap the balls inside. Additionally, as the robot moved forward, the can was further rotated back such that the robot could get closer to the wall for those hard to reach golf balls. Afterwards, the can was lowered back down and the robot would continue on to its next point in the course.

The mechanism was an overall success. However, a few disadvantages with the mechanism are worth mentioning. First, the final mechanism was very wide on the robot and added a few inches to the overall width of the robot. This made it very hard to pick up certain golf balls and make it through the course, especially at points where the robot needed to travel close to the wall. Additionally, we were not able to accomplish a simultaneous drop off of both color golf balls for a few reasons, most significant of which was probably time constraints. With more time, this type of mechanism probably would be capable of simultaneously dropping off blue and orange golf balls to their respective locations. Please see the pictures and videos to gain a better understanding of our gripper mechanism.