Roberto - Balancing Robot

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Roberto - Balancing Robot

• RIT Computer Engineering
• Senior Design Project

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Group Members

• Jeff Mahmood
• Paul Krausman
• Dave Froman

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Project Description

• Two-wheel balancing robot
• Balances on any angled surface
• Remains balances indefinitely
• Remote controlled
• Inverted Pendulum
• PID Controller

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Physical Layout
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PID Algorithm

• Means to control some output from a combination
  of different factors
• Differential equations solved in the frequency
  domain
• We will solve experimentally

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PID Algorithm (cont.)

• PID is Proportional Integral Derivative
• Output based on the aggravate of 3 factors
• Error
• Error Derivative
• Error Integral
• PID algorithm combines these 3 factors to
  determine appropriate output

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Error Definition

• Error Difference between set point and actual
• Error can be positive or negative

Set Point
Error
Actual
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PID Equation

• Proportional Integral Derivative
• Output PT IT DT
• P is the Proportional constant
• Current error
• I is Integral constant
• Sum of past errors
• D is Derivative constant
• Rate of change of error

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Proportional

• Torque applied to motors is proportional to
  amount of error

0
T
40
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Integral

• Sum of all errors over time
• Biases output so all errors cancel over time

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Derivative

• Torque applied to motors proportional to
  derivative of error
• Velocity of error

0
300/sec
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Tuning PID Controllers

• Goal
• Find coefficients for P, I, and D terms
• Robot should snap back to set point after any
  disturbances
• Prevent any oscillations
• Robot should remain at set point indefinitely

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Finding P Term

• Set I and D terms to 0
• Set P term to 1
• Increase P term until strong oscillations occur
• Some references recommend setting P to 60 of
  this value

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Finding D Term

• Slowly increase D until oscillations begin to
  slow
• Fine-tune D
• Robot will oscillate if D is too high
• Robot will fall over is D is too low
• Robot should snap back to set point after any
  disturbances

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Finding I Term

• More difficult than P and D
• Generally inverse of D
• Limit sum to prevent saturation
• Sliding window

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Increase Performance

• Robot may seem sluggish
• If either P or D is set too low, robot will be
  slow to respond
• Robot may oscillate
• If either P or D is set too high, robot will
  oscillate before settling on set point
• Tweak P and D terms until optimal performance is
  achieved

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Sensors

• Accelerometer
• Measures tilt (proportional error)
• Slow response, but accurate
• Gives sense of up
• Gyro
• Measures velocity (derivative error)
• Fast response, but inaccurate
• Suffers from drift over time

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User Interface - Remote Control

• Two axis control left and right motors
• 2 commands for each side move forward, back
• Uses 4 bit encoding/decoding(8 values used)
• Each switch press has unique encode value, which
  is transmitted and received

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Remote Control

• Momentary rocker switches are used for intuitive
  remote controlled car feel
• Robot moves by pressing both switches in the same
  direction, turns by alternating directions

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The End

• Questions???