AME 3623: Project 6: Compasses and Position Control

• All components of the project are due by Friday, April 5th at 11:59pm
• Groups are the same as for project 1.
• Discussion within groups is fine.
• Discussion across groups may not be about the specifics of the solution (general programming/circuit issues are fine to discuss).

At the end of this project, you should be able to:

• extract hovercraft orientation from a magnetometer sensor, and
• use the sensory data to drive the motors in such a way that the craft will orient toward a goal.

Inertial Measurement Units

The IMU library provides the following functions (two of which you already have used):

• imu_setup() initializes the inertial measurement unit. This setup function makes a reasonable guess about your magnetometer biases. However, these may or may not work well for your configuration.

• imu_update() updates the state of the inertial measurement unit. This function expects to be called regularly (at 100-200 Hz).

• imu_calibrate_magbias() is a function that will walk you through the steps of calibrating your compass. Specifically:
  • It will ask you to turn your craft slowly (at a near constant speed). The function expects that you will complete four full revolutions in 40 seconds.
  • After execution of this function, the magnetometer biases will be reset. This function also prints out 3 lines of code that you can place into your setup() function. By including this code, you don't have to call imu_calibrate_magbias() every time you start your program.
  • NOTE: make sure to initialize you serial port before calling this function.

Component 1: Circuit

Component 2: Compass Software and Configuration

• Update your sensor_step() function:
  • It still calls imu_update()

  • If a character has been received from the serial input:
    • If that character is 'c', then this function should call imu_calibrate_magbias()
    • If that character is 'g', then this function should set the heading_goal (a global variable) to the craft's current heading.

  • Continue to display the craft orientation velocity using the linear LEDs

• Implement a new PeriodicAction (called report_task) that executes once per 250 ms

• The associated report_step() function should print out the current state of IMU.yaw

• After calibration, test your compass:
  • Orient your craft such that the compass is reporting zero degrees.

  • Turn your craft by 90 degrees. The reported compass heading should be within about ~5 degrees of 90 degrees.

  • Repeat for the other cardinal directions.

  • If all four headings are reported correctly, then you have a reasonable calibration of your compass and you are done. Make sure that your new magnetometer biases are set in your setup() function (that imu_calibrate_magbiases() printed out).

  • If the headings are not reasonable, then repeat the calibration process.

Component 3: Control Software

Implement the following functions:

• float compute_heading_error(float theta_goal, float theta) returns the difference between the goal and the current heading. Specifically, we are asking what the orientation of the goal is relative to a coordinate frame that is defined by the hovercraft. Return values must range between -180.0 and 180.0 degrees. Positive values correspond to the current orientation being clockwise from the goal.

• float deadband_and_saturation(float error, float deadband, float saturation) takes as input a heading error, a deadband level and a saturation level, and returns a modified error.
  • For an error that is +/- deadband, this function returns a zero.
  • For an error that is larger than saturation + deadband, this function returns saturation
  • For an error between deadband and saturation + deadband, the return value linearly increases with increasing error.
  • and you must deal with the negative side, too.

  • Note: this function must be continuous.

• Your control_step() function should remain the same as in project 5, with the following change:

         float fx = 0.0;
         float fy = 0.0;
         float heading_error = ...
         float modified_error = ...
         float torque = Kp * modified_error;
         set_hovercraft_forces(fx, fy, torque);
         

  where modified_error has already been subjected to the deadband and saturation

  Also, this function should display the current heading error using the heading LEDs (use the negative of value that is returned by compute_heading_error()).

Component 4: Finite State Machine

Component 5: Testing

• Slowly increase Kp until the craft tries to maintain the goal orientation. Holding on to your craft during this stage, simulating rotations by hand, is a good first step in testing.

• After initial testing, you can place the craft on the floor (or a table, if you are careful).

• The craft should produce a thrust in the direction that is the shortest distance to the goal (switching direction at 180 degrees behind the goal)

• We do not expect the craft to precisely stop at the goal. Instead, it will oscillate around the goal (this is okay for now).

What to Hand In

• Demonstration/Code Review: All group members must be present. The demonstration must be completed by Tuesday, April 9th.

• Check in the following to your project 6 area of your subversion tree:
  • Documented code: See the project 1 specification for detailed documentation requirements.

• Personal report: there is no personal report for this project.

Grading

• Each person must accumulate at least three personal programming credits over the course of the semester. This project offers one credit.

• To receive credit, you must be the primary designer, implementer and debugger of the component. This does not mean that your other group members should not be looking over your shoulder. But: you must do the "driving."

• 35%: Project implementation
• 30%: Demonstration of working project (to either of the TA or the instructor)
• 35%: Documentation

Group Grading Rubric

Grades for individuals will be based on the group grade, but weighted by the assessed contributions of the group members to the non-personal programming items.

andrewhfagg -- gmail.com

Last modified: Wed Mar 27 22:31:43 2019