NXT Module: Final Design Report
ENGR 102 – Winter 2013
Engineering Design Lab II
Lab Section:
Group Number:
Section Faculty:
083
Date Submitted:
March FIX, 2013
Section Fellows:
Nick Vacirca
07
Richard Primerano
Dion Antao
Group Members:
Kelly Shiptoski
Maria Nyamukuru
Oyinkansola Aderele
Abstract
Over the past ten weeks in this module, we worked on the design and programming of a Lego
NXT robot and its gripper arm to clear up the mess caused by a train wreck and separate the waste
canisters appropriately using various sensors. We programmed our robot with a program called The Lego
Mindstorm NXT 2.0 program which consisted of ‘blocks’ that made the robot react in certain ways and
helped the sensors work with the code used in programming.
After coming up with a suitable code and design, our robot participated in a competition against
other robots to complete the tasks we were given in the module. We didn’t perform so well in the
competition because forget to take into account the amount of power we used. We put in too much power
in the code we programmed which made the robot tip over the canisters. The robot also seemed to hard
time finding the canisters during the competition.
ENGR 102, Winter 2012
Section 083, Group 07
Problem Statement
In this module, we were presented with a scenario where some waste (nuclear and trash) was
spilled due to a train wreck and we were employed to build a robot that clears up the waste. The nuclear
waste canisters were yellow and magnetic while the trash waste canisters were blue. The robot was
supposed to detect the blue canisters, grab them with its gripper arms and move them towards the light,
detect the yellow canisters, grab them with its gripper arms and move them away from the light towards
another corner and the robot does all of these while avoiding the corners of the wall and other robots.
During the past ten weeks, we had to learn how to use a program called the Lego Mindstorm NXT
2.0 program to program the robot to do small tasks like move in a specific direction and turn in a specific
way. We also had to learn how to program the robot to use sensors including the magnetic sensor, the
light sensor, the color sensor, the ultrasonic sensor, and the touch sensor. After mastering how to use the
Lego Mindstorm NXT 2.0 program to program our robot. We had to design a suitable robot and gripper
arm design and come up with a suitable code that makes the robot perform all of the above tasks
described in the above scenario.
After designing and programming the robot, our robot was to participate in a competition where it
was judged on the amount of canisters it put away in the above scenario in their proper drop off zones. If
the robot won, we would be employed by Robotech to clear up the mess made by the train wreck.
Design Constraints
Some of the design constraints given for the above scenario were the size requirements; our
robot is meant to be able to fit inside a 1’x1’x1.5’ box. That means that the robot, all the attached sensors
and the gripper arm were supposed to fit into the given dimensions which meant limited options for the
design of the gripper arm and the placement of the sensors we used. Also we were only allowed specific
materials outside of the Lego pieces to build our robot. Some of these materials allowed in this constraint
include tape, cardboard, ping pong balls, rubber bands, paper string and drinking straws. We made use of
tape in our design of the robot.
Another constraint was the minimal functionality constraint. This constraint allows that the robot
should be able to demonstrate some basic functions like search for canisters, obstacles and drop off
canisters at their specific drop off zones. We overcame this constraint by using various functions in the
Lego Mindstorm NXT 2.0 program to come up with a programming code that helped the robot to perform
the above tasks.
NXT Platform
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Section 083, Group 07
The NXT kit included many diverse Lego pieces with which the robot was constructed. The NXT also
included the “Intelligent Brick” which was basically the brain of the robot. This “Intelligent Brick” had a 32bit microprocessor. Also, all programs were downloaded onto the robot using a USB cord attached to it.
To run a code, the orange button was pressed. The NXT kit also had multiple motors. These motors were
used in the robot design to turn the wheels of the robot and to motorize the gripper mechanism. Hgh
The Lego Mindstorm NXT 2.0 program provided the ability to program the robot. This was done
by using different “blocks” that were, in the final design, connected to each other through loops. This
program was relatively easy to use because of how visual it was. All loops were orange and literally
appeared as a “loop” surrounding the blocks the affected, the blocks that controlled sensors were yellow,
and the blocks that controlled the motors were green. Each block could then be modified based on
different measurements. For example, a motor block could be set to make the motor rotate for 1 rotation.
Four sensors were used in this robot design: the touch sensor, the magnetic sensor, the light
sensor, and the ultrasonic sensor. The touch sensor was placed at the base of the gripper mechanism so
that when it was triggered, the code then commanded the gripper mechanism to close on the canister.
This was done by using a loop triggered by the touch sensor when it was pressed. The touch sensor was
characterized by testing to make sure a canister would trigger the sensor properly. Much testing also
went into deciding where to place the sensor so that the gripper mechanism could effectively close on the
canister in front of it. Despite all of this testing, in competition, the sensor did not always register being
pressed, and sometimes the gripper mechanism did not close on the canisters properly.
The next sensor that was used was the magnetic sensor. The magnetic sensor was positioned
right next to the touch sensor so that as soon as the touch sensor was triggered and the gripper
mechanism closed on a canister, the magnetic sensor would sense whether the canister was magnetic or
not (nuclear or trash), and then go into the next loop based on this. The magnetic sensor was
characterized by testing the reading of the sensor when it was held up to the magnetic canister. The
trigger value that was chosen was -400. The only downfall of the magnetic sensor is if it was not directly
touching the canister, it would not register its magnetism.
The light sensor was positioned in line with the “Intelligent Brick” because it needed to register the
light, which was a tall lamp in the arena. The robot was programmed to, once it had a non-magnetic
canister, go move toward the light until it was a certain distance from the wall, and then drop off the
canister and go back to the beginning of the entire loop. The light sensor was testing many times until the
final value of greater than 58 (intensity) was decided upon. This value worked well in most areas of the
arena because the robot registered the light and moved toward it. The downfall of the light sensor was
that sometimes the robot registered the light too soon, and then the canister was dropped off well before
the drop-off zone.
The final sensor used was the ultrasonic sensor, which was placed between the arms of the
gripper mechanism so that the sensor would not be affected by sensing them. The sensor also had to be
placed above the level of the canisters. The sensor was approximately 3-4 inches above the ground, so
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that it would sense the 4 inch high wall. The robot was programmed that once it was in the high light
intensity zone with the canister, it would sense the wall at a certain distance and drop off the canister. It
was also used in a touch sensor loop so that while the robot was waiting to be triggered by touching a
canister, it was avoiding any of robots or walls that came within 23 centimeters of the robot. This distance
was tested multiple times, and the value that was used was less than 23 centimeters. This sensor was
very tricky to work with, and it often did not recognize the wall in time and never dropped the canister, or
recognized it too early and dropped the canister in the middle of the arena.
Initial Design
1) MECHANICAL DESIGN – The robot was constructed completely out of Legos provided in the
NXT robotics kit. There are two motors controlling the tires of the robot. One motor is attached to
the front (the end with the two larger tires). This motor is used to control the gripper. The gripper
is what will push the waste containers to their designated locations. The gripper design is that of a
claw. It is constructed with four curved Lego pieces, two on each side, to simulate a claw. This
claw will then effectively enclose the waste containers and push them toward their designated
locations. To differentiate between the nuclear waste containers and the trash containers, the
robot will be equipped with sensors. So that the robot moves in the direction of the nuclear waste
containers, it will be equipped with a sound sensor, because the nuclear waste will be emitting
sound. The touch sensor will tell the robot when it has touched the container. It will then proceed
to the nuclear waste depot to drop off the nuclear waste. When the robot touches a trash
container, it will be programmed to recognize that it is not emitting a sound and so should not be
taken to the part of the arena where the nuclear waste depot is. Instead, the robot will be
programmed to move toward the bright area (where the trash landfill is) using the light sensor.
These sensors will be attached to the robot above the claw. Figure 1 (below) is an accurate
representation of the prototype of the robot. It shows the gripper mechanism and the general look
of the prototype. The sensors will be attached to the robot just above the gripper mechanism.
Figure 1. Proposed Robot Design.
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2) ALGORITHM DESIGN – Below is a step-by-step process (similar to a flow chart) explaining the
way the robot is meant to operate.
START:
1. Does the color sensor detect color?
YES: Runs both motors forward
NO: Runs motor forward and robot spins
2. Is the touch sensor pressed?
YES: Stops motors and gripper closes
NO: Runs motor forward
3. Does magnetic sensor detect magnet?
YES: Runs both motors forward
NO: Runs both motors forward
4. Magnet detected: is light sensor detecting light intensity less than 15?
YES: Runs both motors forward
NO: Runs motor forward and robot spins
5. Magnet not detected: is light sensor detecting light intensity greater than 50?
YES: Runs both motors forward
NO: Runs motor forward and robot spins
6. Magnet detected/light < 15: is light sensor detecting light intensity less than 10?
YES: Stop motor and gripper opens
NO: Runs motor forward
7. Magnet not detected/ light intensity > 50: is light sensor detecting light intensity > 90?
YES: Stop motor and gripper opens
NO: Runs motor forward
END
Final Design
1) MECHANICAL DESIGN – The final design of the robot, like the initial design, was completely
constructed out of Legos. Two of the wheels are controlled by their own motors. One motor is
attached to the front (the end with the two larger tires), but the final orientation of the motor was
that it was turned 90 degrees for the new design. This motor is used to control the gripper. The
new gripper will now, instead of gripping, enclose the containers and push them to their final
designated locations. The gripper design is that a square of Legos that comes down from above
and encloses the container. To differentiate between the nuclear waste containers and the trash
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containers, the robot will be equipped with sensors. So the robot avoids the wall and other robots,
it will be equipped with an ultrasonic sensor. The robot will do this until it touches a container.
Then it will sense whether it is magnetic with the magnetic sensor. If it is a nuclear container
(magnetic) it will let go of it. If it is a trash container (non-magnetic), the gripper will close on the
container. Then, the robot was programmed to search for light with the light sensor because that
is where the drop-off zone for trash containers was. Once the robot registered a certain light
intensity, it was programmed to release the canister when it was a certain distance from the wall
(using the ultrasonic sensor again). The touch and magnetic sensors were positioned below the
gripper mechanism, and the light and ultrasonic sensors were above it. Figure 2 (below) is an
accurate representation of the final robot.
Figure 2. Final Robot Design.
2) ALGORITHM DESIGN – Below is a step-by-step process (similar to a flow chart) explaining the
way the robot was meant to operate.
START:
Is the touch sensor pressed?
YES: Closes gripper on container
NO: Avoids walls and other robots by backing up and turning around
Is the canister magnetic?
YES: Opens gripper and goes back to beginning of the loop
NO: Begins to search for light
Is the light intensity greater than 58?
YES: Moves forward one rotation at a time
NO: Continues to spin in a zero point turn until light is found
Is the wall detected?
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YES: Opens gripper, backs up, turns around, reverts to beginning of the loop
NO: Moves forward one rotation at a time
END
Competition Performance
During the competition, a score of 80% was attained due to failure to drop any canister in the
drop off zone. The biggest problem encountered by the robot during the competition was instability on the
ground. Whenever one of the tires tried to move over or past a canister, the robot would fell over and lay
sideways. This is because the robot had a smaller surface area in comparison to the robot’s height. The
flipping over is also due to high power in the motors. Another problem encountered was the robot got
stuck on the wall. It had been programmed to back up if the ultra-sonic sensor detected a wall. However
since the ultra-sonic sensor was placed at the front, if the side of the robot got stuck, the ultra-sonic
sensor was unable to detect the wall. The reason the robot got stuck on the wall was that the gripper
designer had a part that was projected outwards. This projection got stuck in the spaces in the fence.
When the robot was headed to the light with a canister and another robot passed by it would sense this
robot and so dropped the canister off at that spot which wasn’t the drop off zone. The robot also had a
hard time finding canisters. It would just move in circles.
Conclusions
The robot avoided the wall, and avoided other robots because the ultra-sonic sensor was placed
at the front of the robot. When the touch sensor was pressed, the gripper closed on the canister and the
robot moved towards the light. The gripper actually caught the canister because it was designed like a net
and fully enclose the canister. However the delivery of a blue canister to the drop off zone only occurred
in perfect conditions. Because of the code, there was no particular way to search for canisters and move
towards them. The general design of the robot could be improved by increasing the surface area and by
reducing the motor power in the code to make it more stable. The projection in the gripper could be
removed or a wheel could be placed at the end of the projection so that when it gets to the wall, the wheel
turns and makes the gripper move so reducing chances of getting stuck in the wall. To avoid dropping the
canister at the wrong spot because another robot passed by, the ultra-sonic sensor could be coded twice,
if it senses an obstacle the first time, it should stop and wait and then sense again, if the obstacle is still
there, then it’s the right drop off zone, if not it should keep moving towards the light.
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References
List your references here in IEEE standard formatting. If needed, search online for the IEEE
Citation Reference. When referencing a document in the text, do it as in the following example sentence:
“earlier work reported elsewhere came to a similar conclusion [1-3]”. This will instruct the reader of the
sentence to go to the references section and look up references [1], [2], and [3] for supporting
information. These enumerations come from the IEEE bibliography formatting. Things that you should be
referencing include:
1. The module overview document
2. The competition procedure document
3. Any additional sources that document the basis of your design
Every resource listed here must be cited in the narrative of the report using the IEEE formatting style (see
the reference formatting guide linked in this section).
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