Application of a PID controller and
Bluetooth communication
Computation & Modeling
Jade Mills, Gage Hibner
Northwest Halifax High
2010
South Mecklenburg High
NXT Programming
 All of our robots were programmed using the NXT
programming software.
 NXT is a program that allows the user to explore
programming from the basic to complex levels .
 The program uses blocks to map out the programs
actions
 NXT gives the robot “senses” by working with light,
touch, ultrasonic, time, and rotation sensors.
NXT Programming
 An example of a simple
program using NXT
 It tells the robot to pivot
to the left until it sees
white then it will stop
breifly.
Can You Rock with this Balance?
Our robot was designed
to resemble a segway,
meaning it was created
to balance on two
wheels while only
using three motors and
a light sensor
We also included an
ultra sonic sensor for a
visual effect
PID Controller
 The balancing-bot was made possible by the PID
controller.
 A PID controller uses three terms to calculate a way to
fix an error from a set point.
 An easy way to think of it is as a controller that self
adjusts to go back to the starting position.
 A real life analogy of a PID controller is starting a bath.
To get the perfect water temperature you have to adjust
the hot water by turning it down or adding cold water.
 The three terms are the proportional, the integral, and
the derivative term.
Proportional Term
 The proportional term
calculates error by taking
the distance from the set
point and multiplying it
times a number, Kp,
proportional to the error
created to try and move
back to the original
position.
Integral Term
 The I (integral) term
calculates the error over
the time and multiplies
it by the value of the
integral gain, Ki. The I
term is accurate but
often produces a lot of
overshoot which causes
the robot to fall. The
reason for this is because
the I term corrects over
long periods of time
Derivative Term
 The D term calculates
the error by determining
the slope over time. The
derivate value also slows
the rate of change, this is
rather important
because it contributes
mostly to stability
because it deals with the
overshoot produced
from the I term.
Proportional-Integral-Derivative
 The big picture.
Results
TERM
ORIGINAL
VALUE
CHANGE
MADE
NEW VALUE
RESULT
Proportional
40
50% increase
60
Faster
response but
instability
Proportional
40
50% decrease
20
Complete loss
of balance
Integral
3
Multiply by 2
6
Shorter
distance better
stability
Derivative
20
25% increase
25
Longer
distances
Great stability
Robotic Interactions
 Robots can interact with each other by using
Bluetooth.
 Our program created in NXT tells the balancing robot
which direction to move based on the position of the
slider .
Robotic Interactions
 This program contains a
Boolean that says when
the slider is far from the
ultrasonic sensor it sends
a true message to the
balancing robot to move
forward.
 When the slider gets
closer to the ultrasonic
sensor it sends a true
message to move
backwards.
What we Learned!
 A new programming language, NXT.
 How a PID controller works.
 We gained a greater understanding about how
Bluetooth technology works.