Uav landing

https://groups.google.com/group/uavdevboard-dev/browse_thread/thread/66dd3db5feeed981
 - Clean data from the ultrasound
 - revise range data to account for bank and roll (fairly easy) (i.e.
 determine vertical range to ground).
 - The system, with no "look ahead", is only really suitable for flat
 landing fields.
 - Feedforward control, understanding the characterstics of the plane
 close to stall, along with drag characterstics, may be vital.
 - Good landing may require a good understanding of the "transfer
 function" of the plane for pitch control, but since we are operating close
 to the stall, the mathematical model may be invalid.
=== notes ===
 - Ensure we have frequent and accurate trustworthy data from the Sonar
 Height Above Ground sensor.
 - We may need an "observer" style Kalman Filter, in order to get
 quality data.
 - Raw data is only fed 10 times / second from Sonar.
 - At 10.0 m/s and 20 degree pitch down, the plane is descending at
 least at 3.4 m/s. If the beam is working at up to 7 meters from ground,
 then that provides a valid return from 7.0 * cos(20), which is 6.5 meters
 above ground. In other words, the flare must occur within about
1 second of
 flight, in order to flare safely, 1 second before hitting the
ground ! Not
 much room for an error margin. Of course those figures improve if the
 intial descent rate is less thatn 20 degrees.
 - The entire concept of downward looking Sonar implies the landing
 site is flat, or gently sloping. Sudden changes in slope will not be
 detected in time.
 - We probably need our plane's to be optimally set up for control of
 height by the AutoPilot. The best way to do that, is to learn how Bill has
 extracted the control Transfer Functions for Pitch and Roll from his Quad,
 and apply that type of technology to pitch control, and height control of
 the plane. Then, with transfer function in hand, we can model the entire
 flare control algorithm in a mathematical simulator like the Open
SourceXcos<http://www.scilab.org/products/xcos>(similar to Simulink
for MatLab).
 - Only once we have successfully modelled the landing in Xcos, with
 typical noise to the Sonar, would I really want to embark on coding up the
 solution. I enclose a sample (made up), options.h entry for Sonar Flare and
 Landing.
////////////////////////////////////////////////////////////////////////////////
// MAXBOTIX SONAR TERRAIN FOLLOWING AND LANDING FLARE
// Designed for use with the following device:-
// http://www.maxbotix.com/Ultrasonic_Sensors/MB1230.htm
// Can be used on INPUT 8 of the UDB4 if that is not used for other
purposes.
// Will compensate for roll / pitch, subject to receiving a returned sonar
signal.
//
// This option is for UDB4 only
// Height is returned 4 times / second in centimers in SERIAL_UDB_EXTRA PWM
channel 8.
//
// NOTE: Requires Auto Pitch PID adjustment to be enabled.
// Auto Pitch PID will auto adjust your plane for the best possible PID
control of height.
#define AUTO_ADJUST_PITCH_PID 1
// SONAR_STABILIZED_TERRAIN_FOLLOWING
// In stabilized mode, the plane will attempt to stay above a minimum sonar
height from ground
// using Throttle and Pitch. If Throttle is cut to zero, the plane will
glide in.
#define SONAR_STABILIZED_TERRAIN_FOLLOWING 1
#define SONAR_STABILIZED_MINIMUM_HEIGHT 2.0 // Meters. Minimum
1.0, Maximum 6.0
// SONAR LANDING FLARE
#define SONAR_LANDING_FLARE 0
#define SONAR_FLARE_DESCENT_RATE 0.3 // Meters / Second. 0.3 is
default value.
#define SONAR_FLARE_START_HEIGHT 4.0 // Meters. Minimum 1.0, Maximum
6.0. Start High !
Category:Gentlenav