Robotics Exam 1

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coffeya
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308626
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Robotics Exam 1
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2015-09-28 10:57:59
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Robotics
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Exam 1
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  1. Robots are typically comprised of the following major subsystems
    • Mechanical
    • Electrical Power and Signals 
    • Sensing 
    • Software
  2. Primitives of Robotics
    • Sense
    • Plan 
    • Act
  3. Program Control Levels
    • Teleoperator: responds to user-supplied commands 
    • Blind mobility: executes a program of instructions  
    • Teach/playback: copies historical behavior of itself 
    • Convoy: copies behavior of another vehicle
  4. Supervised control
    Operator specifies broad goals at various frequencies
  5. Analog connections are used to transmit a
    voltage to the device
  6. Parallel communication
    transmits several streams of data simultaneously along multiple channels
  7. Serial communication
    is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus
  8. Benefits of Serial communication
    Less mass, don't have to worry about interference
  9. Serial sends information
    one bit at a time
  10. Serial has specific timing requirements, specified by
    baud rate, similar to a bar code
  11. A bus is used to transfer
    digital information between components
  12. A bus uses a specific
    protocol for reading digital signals
  13. A bus would be like a human
    spine
  14. Information transfer over a bus typically has a
    host and at least one device
  15. The host offers
    information, resources, services and applications to a device
  16. A device is connected externally or internally to the host and is
    directed and used by the host
  17. Host and Device relationship is in many ways a
    slave and master relationship
  18. Controller Area Network (CAN)
    • Primarily in automobile industry
    • Automatic retransmission of corrupted messages as soon as the bus is idle again
    • Priorities are given to messages based on importance
  19. Inter-Integrated Circuit (I2C)
    • Master/Slave Serial Bus
    • Used when low cost is more important than speed
  20. TCP
    • Synchronous
    • Built in error detection and correction
    • High Reliability, low efficiency
    • (Ex: Webpage)
  21. UDP
    • Asynchronous
    • Error detection, no correction
    • Low reliability, high efficiency
    • (Ex: streaming)
  22. ASCII Encoding
    • Human readable
    • Easy to debug
    • Easy to program
  23. Binary Encoding
    • Pack more data into fewer number of bytes
    • Computationally more efficient
  24. Asynchronous
    • Occurs at any time without warning
    • Variable bit rate
  25. Synchronous
    • Steady stream of data
    • When stream ends, communication is considered terminated
  26. Commonly used data fields
    • Start Byte/Bit
    • Message ID
    • Packet Size
    • Addressing for point to multipoint
    • Out of Order Checking – timestamp, sequence number
    • Error Checking – Checksum, CRC
    • Error Correction
  27. Start/End Bit/Byte
    Needed in synchronous, stream-based transport–To tell where stream ends/starts
  28. Out of Order
    Time Stamp
    –Sender includes a timestamp in every message and receiver compares timestamp to previous messages
  29. Out of Order
    Sequence Number
    –Sender includes a unique sequence number for every message. Increment by one for every message sent
  30. Error Detection Types
    • Parity
    • Checksum
    • Cyclic Redundancy Check
  31. Error Correction
    ACK/NAK
    • Simplest form of error correction
    • Ignore data with errors, ask for data to be sent again
  32. Error Correction
    Hamming Codes
    • –Redundant data
    • Inefficient, lots of extra data
  33. Pulse-Width Modulation (PWM) is another form of
    Digital communication

    signals are pulsed and pulse width indicates value
  34. PWM has relatively low power losses.Makes it an efficient way of encoding _____ signals
    analog
  35. Information bandwidth is ______ proportional to frequency
    directly
  36. Fundamental trade-off:
    propagation vs. bandwidth
  37. Signal degradation is ______ proportional to frequency
    inversely
  38. High frequency =
    Low frequency =
    • lots of data
    • long range
  39. Radio Transmitters
    • Encode information and generate electric output signal at acceptable power level
    • Signal must be modulated around carrier frequency
    • Most modern radios are digital
  40. Spread Spectrum
    Greater data rates can be achieved via using distributed carrier waves (spread spectrum)
  41. Frequency Hopping Spread Spectrum (FHSS)/ Time Domain Multiplexing (TDM)
    • Pseudorandomly jumps between carrier channels
    • Robust to Doppler shift = good for aerial
  42. Orthogonal Frequency Division Multiplexing (OFDM)
    • Transmits on multiple frequencies simultaneously
    • Robust to interference and multipath = good for ground
  43. Ideal "isotropic" antenna tranmits
    Equal power in all directions
  44. Antennas
    • Convert electrical power and RF waves
    • Must be matched to transmitter
  45. Gain is the increase in radiated power relative to the
    ideal isotropic model
  46. Total power
    does not change
  47. Omnidirectional Antennas
    Radiate power in “all” directions equally
  48. Directional Antennas
    • Focus power in one direction to achieve gain
    • More gain = narrower band
  49. Radio Receivers
    Filters and processes electrical signals from antenna to decode signal
  50. Radio Receivers
    Two important factors
    • Signal-to-Noise Ratio (SNR)
    • Receive sensitivity
  51. Cabling and Connectors
    • Significant signaling losses occur in cables and connectors
    • Losses increase with frequency
  52. Radio Units
    Power is typically expressed in dB
  53. RF power often uses
    Antenna gains expressed in
    • dBm
    • dBi
  54. Pulse-Width Modulation (PWM) is another form of ________ communication
    digital
  55. Pulse-Width Modulation (PWM) signals are
    pulsed and pulse width indicates value
  56. Pulse-Width Modulation (PWM) signals have relative
    low power losses and makes it an efficient way of encoding analog signals
  57. Given a robot’s geometry and the velocity of its wheels, how does the robot move?
    Forward Kinematics
  58. Given where a robot needs to move and robot geometry, what wheel velocities are required for motion
    Inverse Kinematics
  59. Wheel Kinematic Constraints Assumptions
    • Movement on horizontal plane
    • Point contact of the wheels
    • Wheels not deformable
    • Pure rolling ( = 0 at contact point)
    • No slipping, skidding or sliding
    • No friction for rotation around contact point
    • Steering axes orthogonal to the surface
    • Wheels connected by rigid frame (chassis)
  60. Given a robot with M wheels. What wheels impose constraints ?
    Only fixed and steerable standard wheels impose constraints
  61. In a plane you only have three degrees of freedom which can be controlled via:
    • Wheel Steering
    • Driven Wheels
  62. Why do we prefer to control the degrees of freedom via driven wheels?
    Must have one and are easier to control
  63. A holonomic constraint can be expressed explicitly in terms of
    position
  64. A nonholonomic constraint requires expression in terms of
    erivatives
  65. An omnidirectional robot can move at any time in any direction along the ground plane (x,y) regardless of the orientation of the robot around its ____ axis.
    vertical
  66. Is the fixed wheel sliding constraint holonomic?
    No
  67. Note that robots with only holonomic constraints are considered
    holonomic robots
  68. Differential Steering
    • Two Drive Wheels
    • Caster for Stability
  69. SKID Steering
    • Wheeled and tracked
    • Wheels slide and slip
  70. Ackerman Steering
    • Front Wheels Rotate
    • Not Parallel Steering!
  71. High Maneuverability
    Skid, Differential
  72. Energy efficient
    Ackerman, Differential
  73. Good for Off-road Use
    Skid, Ackerman, 4-Wheel
  74. Low Mechanical Complexity
    Differential, Skid
  75. Easy to Model
    Differential, Ackerman, 4-Wheel
  76. In quasi-static stability any snapshot of the robot shows that the robot is
    statically stable
  77. A robot must have at least _ legs for quasi-static walking stability
    4
  78. Why must a legged robot maintain ground contact for it to have a kinematic model?
    gravitational force
  79. Aerial vehicles do not have kinematic equations because of
    gravitational forces
  80. Proprioceptive sensors measure
    values internal to the system, for example, engine temperature, motor speed, wheel speed, vehicle acceleration,
  81. Exteroceptive sensors
    acquire information from the environment, for example distance measurements,
  82. Passive sensors measure
    ambient environmental energy entering the sensor
  83. Active sensors
    emit energy into the environment, then measure the environmental reaction
  84. Ideally, the analog output or digital signal value will be proportional to the
    measurement
  85. Systematic error also known as a
    deterministic errors

    caused by factors that can (in theory) be modeled -> prediction
  86. Random error also known as a
    non-deterministic

    no prediction possible
  87. describes the closeness of output readings when the same sensor input is applied repetitively over a short period of time and the same experimental conditions
    Repeatability
  88. describes the closeness of a sensor's readings when there are changes in the experimental conditions.
    Reproducibility
  89. It is normally desirable that the output reading of a sensor is _____ proportional to the quantity being measured.
    linearly
  90. Typical types of nonlinearities
    hysteresis and dead space
  91. describes the effect in which the zero reading of an instrument is modified by a change in ambient conditions.
    Zero drift or bias
  92. defines the amount by which an instrument's sensitivity of measurement varies as ambient conditions change
    Sensitivity drift (also known as scale factor drift)
  93. ratio of output change to input change
    Sensitivity
  94. sensitivity to environmental parameters that are orthogonal to the target parameters
    Cross-sensitivity
  95. Eliminating Noise
    Hardware and transmission lines
    • Shielding 
    • Using twisted pair wires
  96. Eliminating Noise
    Signal processing
    • Kalman Filtering
    • Particle Filtering
  97. measuring instrument describe the behavior between the time a measured quantity changes value (from one constant to another) and the time when the sensor attains a steady value in response
    dynamic characteristics
  98. An  example of a zero order instrument
    potentiometer
  99. Example of a  first order instrument
    liquid-in-glass thermometer
  100. Example of a second order instrument
    accelerometer
  101. used to measure the speed with which a sensor can provide a stream of readings.
    Bandwidth
  102. Formally, the number of measurements per second is defined as the sensor's frequency in
    hertz.
  103. IP ratings are expressed with two (or three) numbers. 
    First number = 
    Second number = 
    Third number =
    • solid objects
    • liquid
    • mechanical impacts

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