Project 4: Height Control

Project Goals

• design and implement a real-time sensor control interface,
• implement an "integration" control scheme, and
• make modifications the design of a finite state machine.

Hardware Overview

Each test station is equipped with a Devantech sonar sensor unit and a compass. Each sonar unit is equipped with a sonic transmitter which will emit a small burst of clicks. The receiver will sense the signal that has reflected off of some surface. By measuring the return time of the signal, we can infer the distance to the surface.

For the heli stations, the sensors will be placed underneath the helicopter (facing upwards). This way, we can measure the height of the heli at a given time. We will then use this information to hover the heli at some specified height.

The interface to the sonar unit is as follows:

• White wire: sonar command.
  • Bring this line high for at least 10 usec.
  • Once it is returned to a low state, the sonar will produce a brief sonic burst.

• Green wire: signal return.
  • Once the sonic burst is complete, this line will be brought high by the sonar itself.
  • When the reflected signal is sensed, this line will be brought low (between 100 usec and 18 msec later).
  • If no reflected signal is observed, the sonar will timeout and bring this line low at about 36 msec.

Note: After the reflected signal has been detected, you must wait for at least 10 msec to command the next sonic pulse.

Project Components

Part 1: Microcontroller Circuit

Part 2: Sensing Distance

• Produces the appropriate sonar control signal.
• Measures the duration of the pulse from the sonar.
• Once the pulse is measured, places the resulting value into the global variable:

  volatile int16_t global_duration;

  If there is an error, this variable should be set to a value of -1.

Part 3: Height Display

• Implement a function:

  int16_t get_height(void)

  That will safely read the value from global_duration and return the height of the craft (i.e., measured distance) in millimeters.

  By safely, we mean that this variable should be accessed without being interrupted by the ISR.

• Display the height using the "velocity" LEDs.

Part 4: Height Control

• Given a height goal, alter the throttle command until the current height matches the height goal.

  Because your throttle command is not an acceleration (due to the dangling wire), an appropriate implementation is to use an integration controller.

  Your main loop will have an additional component:

             throttle_command += Ki * (height_goal - height_current) / 100;
  
             #Insert code to ensure that throttle_command remains in the valid limits#
  
             set_throttle((uint8_t) throttle_command);
  
  

  Note: the divisor of 100 will essentially allow you to express fractional integration gains (i.e., your effective gain is Ki/100)

• Modify the finite state machine implementation so that heli performs the following sequence:
  • Rise to approximately 50 cm
  • After obtaining 50 cm, wait for 20 seconds
  • Rise to approximately 100 cm
  • After obtaining 100 cm, wait for 20 seconds
  • Land

  Hint: you will need a deadband around your height goal.

References

• Atmel HOWTO
• OU-XUFO hardware specification
• Devantech sonar sensor unit

What to Hand In

• Demonstration/Presentation: All group members must be present.
  • Demonstrate your final product.
  • Present your design and implementation (5 minutes). The group is responsible for assembling a short presentation consisting of 3-4 slides (on computer or in printed form). Describe the design including:
    • Your general approach to solving the problem,
    • any key software algorithms (how the general problems are solved in code), and
    • the software organization (describe how the software problem is split into different separable sub-problems, and how the different components interact).
    • DO NOT include low-level code
    • Hand in the power point file to the project 4 digital dropbox.
• Code: Turn in your documented code to the project 4 digital dropbox on D2L (hand in the ".c" file). Only hand in one copy of the code per group.
• Personal report: One submission per person to the project 4 digital dropbox. State the relative contribution of you and your group members (in terms of percentage of effort) (text format only!). This distribution will be used to compute the individual grades.

Grading

• 40%: Project implementation
• 30%: Demonstration/presentation of working project (to the TA or the instructor). This demonstration is due at the same time as the reports
• 30%: Code documentation and group report

Grades for individuals will be based on the group grade, but weighted by the assessed contributions of the group members.

fagg [[at]] cs.ou.edu

Last modified: Mon Apr 20 21:16:01 2009