Blimp Guidance Requirements

1
Blimp Guidance Requirements

• Near-term
• Waypoint to waypoint path control at constant
  altitude
• Path commands generated solely past and next
  waypoint locations
• MARS2020 Demo
• 5 dimensional path control
• x, y, z position, heading, and time of arrival at
  each waypoint

2
Blimp Guidance Control Law OverviewNear term
Control Approach

• Blimp will be operated at constant speed in route
  to waypoints ( 1 m/s) loiter at a specified
  waypoint will require upgrade to blimp thrust
  configuration.
• Constant Altitude will be used to simplify path
  planning to a series of steering commands
  (controlled through thrust tilt)
• All position guidance will be computed based on
  last and next waypoint locations
• Guidance control law will switch through sequence
  of waypoints as the blimp progresses through its
  flight plan
• A tolerance on proximity to next waypoint will be
  used to switch the guidance law to shift the
  stack of waypoints
• Cross track and track angle errors will be used
  to close loop on position
• Waypoints must be relatively widely separated
• Proximity of adjacent waypoints and changes in
  desired course angles cannot exceed turning
  capability of blimp at nominal speed

3
Parameter Definitions
North
Waypoint Capture Proximity
Next Waypoint
Track Angle
Groundspeed
Heading
Track Angle Error
Desired Track
Present Position
Along Track Error
Cross Track Error
Waypoint stack (last/next) shifts when Along
Track Error lt Capture Proximity
Course
East
Last Waypoint
4
Waypoint to Waypoint Guidance Control Laws
Steering Commands
Cross Track Error (m)
Lateral Steering Command (rad/sec)
Cross Track Gain
Track Error Gain
Course (rad)
Ground Track Angle (rad)
Typical Flight Path for Three Waypoints
5
Blimp Control Law Mixing to
Hardware Commands1. Feedback
gains will be proportional and will relate
position and orientation errors to force and
moment commands in inertial axes2. Nonlinear
inverse of actuator force and moment
configuration will be used to mix position errors
to motor commands

• Groundspeed used to generate nominal thrust level
• Nominal motor speed based on nominal drag
  estimate for blimp in axial flight
• X Y Position and heading used to generate
  steering commands
• Differential thrust
• Rudder position
• Z position (altitude) used to generate thrust
  vector command
• Propeller tilt angle
• Moment effect on blimp considered negligible at
  nominal thrust levels

Fx (TpTs)cos(mq) Fz (TpTs)sin(mq) Mz
(Tp-Ts)lcos(mq)
q zero
m
6
Building Block Approach to Demonstration of Blimp
Capability

• Gondola suspended from single point
• Demonstrate stability of turning control law in
  lab (without stabilizing effects of blimp
  damping and inertia)
• Single waypoint navigation (capture from
  arbitrary starting point and heading establish
  practical tolerance on capture distance)
• Indoor
• starting point within cone of vision of single
  ground-based pan/tilt camera (current capability)
• Starting point anywhere in indoor space (using
  single downward iBot camera with grid of color
  markers (approximate spacing altitude of blimp)
• Outdoor
• Use available GPS system (currently integrated)
• Multiple waypoint navigation
• Upgrade control law to shift stack of waypoints
  once all single point demonstrations are
  successful
• Stability demonstrated for altitude and ground
  position closed loop control laws
• Capture distance reliable

7
Blimp Status (11/11/02)

• Control developed waypoint navigation for
  x,y,z,heading commands
• Sensor signals currently available for outdoor
  flight
• Sensor signal synthesis through vision in work
  for indoor flight
• Limited ability for single waypoint currently
  available with ground-based camera
• Wide-area capability will require different
  approach
• Grid of markers on ground for dead-reckoning
  navigation using single blimp mounted web-cam
  recommended
• Navigation algorithm must be developed to
  interpret sequence of color markers
• Minimal setup/calibration required
• Simulation model developed to size feedback gains
• ROCI 2 code in work for control laws
• Testing sequence will start as soon as code is
  available
• Lab
• Indoor
• Outdoor