The Robot Proposal is divided into couple design components:
End Effectors: fork flipper and cable claw
Motors: 2 Power Function and 3 NXT motors
Drivetrain: rear wheel drive, 2 wide flat rubber tires, 1 tank tread, 2 front skis
Sensors: EOPD, compass, ultrasonic sensors
Accessories: IR Link, Magnets, Video Camera
End Effector
The primary end effector selected for our robot is the fork flipper to flip the loops into a hopper. This loop flipper is fast and picks up loops easily by using the EOPD sensor to sense the location of the loops and determine the distance away based on the brightness of reflected light, so the robot can adjust its position accordingly. Only one NXT motor is needed.
To save time and increase accuracy, we will also use a cable claw to retrieve the water ice loops inside the craters. The main difference between this cable arm and the previous parallelogram or linear actuator arms we tried is that it’s lighter and can reach below the mounting plane of the arm pivot point. Instead of using gears like the claw arm, the cable claw uses LEGO strings and pulleys to provide powers to the mechanisms with the bulk of the motors and battery weight mounted on the robot as counterweights for the arm. Just like the fork flipper, the EOPD sensor will be used to detect the loop’s locations. The cable claw will be in the vertical position during the start of the mission to stay inside the size limit.
Drivetrain
Our drivetrain contains 2 NXT motors that each control a wheel to make a rear wheel drive robot that is good for turning. A pair of “skis” will be mounted in the front to assist in going up the ridge. Large, flat, low profile tires (tires not shown on rendering since they are not available in LDD library) can improve accuracy and increase traction . The alternating pattern tires (as shown for rendering purpose) were less accurate on the LEGO mats when we tested them. A tank tread (not shown since not available in LDD library) runs along the underside of the robot between two tires to provide pulling power over the lunar ridge. Only one wheel will power the tank tread so the motors can still turn, move forwards and backwards independently.
Sensors
Although we tested other types of sensors (gyro, accelerometer), three other sensors were selected for the robot to locate its position: the EOPD sensor, the compass sensor, and the ultrasonic sensor. Each sensor will be made with a second or even third function for additional robot navigation and end effector control.
The EOPD sensor will be mounted low in-between the front skis. It is a long range light sensor that can be used to detect the loop by showing spikes in light value as the loop is passed in front of the sensor. It can also assist in wall-following by telling the robot to stop when it reads a certain light value from the wall. The EOPD also has a third function: crater and ridge detection. The EOPD sesnor is mounted at the same height as the crater wall pieces so this allows the robot to know it is near the crater or ridge so it can begin the next section of the program.
The compass sensor will be mounted on the top of the robot to report an accurate heading by telling how many degrees the robot is off from north so the robot can move in any direction accurately while still knowing the target direction. If a second arm is added, the compass sensor can also be used to monitor the position of the arm. A LEGO magnet will be attached to the arm so as the arm extends, the LEGO magnet will pass through the range of the compass sensor, disrupting the readings. From the disruption of the compass readings, the robot knows when the arm has extended. The compass sensor will resume its original function when the arm is retracted and is out of range.
The ultrasonic sensor will be mounted on the top and face the side for wall-following at a desired distance using the PID (proportional integral, derivative) program, while the EOPD readings will act as the condition to tell the robot when to stop. The ultrasonic sensor is also used as an inclinometer to tell when the robot is on an incline. This is done by using a pendulum to block out one of the “eyes” of the ultrasonic sensor. When the robot obtains an abnormal ultrasound reading, it knows that it’s on the ridge or ramp and will run its program accordingly.
Motors
Three NXT motors are used for the end effector and drivetrain for the primary robot design.
In order to provide the range of motion necessary to retrieve the loops, the Cable Claw will require multiple Power Function motors controlled by a HiTechnic IRLink sensor. The IRLink allows 8 additional Power Function motors with just one NXT sensor port by sending infrared commands to each one of the four Power Function IR Receivers that can each control 2 motors. The arm for the claw will be controlled by Lego strings and pulleys each driven by a Power Function motor. The entire arm will be able to retract in the starting position, extend and reach for the loops, pick them up, and drop the loop into the hopper.
Frame
The robot is made of beams and Technic pieces to create a sturdy frame. The NXT LEGO Brick is placed in the lower-middle part of the robot to evenly distribute the weight and create a low center of gravity. By doing so, the robot is less likely to tip over when attempting to cross over the ridge or going on an incline.
Video Camera
Although the video camera isn’t a main part of the robot, it is still vital to video tape the robot’s movement and capture the Heritage Artifacts in Phase 2. The camera will be attached on top of the EOPD sensor using dual lock tape so that it’s not too high that the feed will be shaky, nor is it too low that the ridges and craters can block the view.
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[...] members from FLL, FTC and FRC teams, signed up to compet in Phase 1 by submit a video essay and robot design proposal rendered in either LEGO Digital Designer or L-Draw. From there, based on the robot design [...]