AME 3623: Project 7: Rate Gyroscopes and Damping Control

Key to successful control in embedded systems is the ability to integrate information about the external state of your system into the control decisions that are being made. In this project, we will finally close a loop between sensing and actuation. We will add one more component to your circuit: an inertial measurement unit (IMU). The IMU contains three distinct sensors (with three degrees of freedom each): an accelerometer, a rate gyroscope and a magnetometer. The gyroscope will be used in this project to dampen rotational disturbances. In project 8, we will use all nine degrees-of-freedom to estimate the orientation of the hovercraft.

All components of the project are due by Tuesday, April 13th at 5:00 pm.
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 rotation rate information from an inertial measurement unit, and
use the sensory data to dampen out rotational disturbances.

Component 0: Library Installation

Download and install the following libraries:

At the top of your project, include the following lines:

#include "ImuUtils.h"
#include "PeriodicAction.h"       
#include "PWMServo.h"

The new IMU Utils library provides the following functions:

imu_setup() initializes the inertial measurement unit. This function assumes that your hovercraft is not in motion when it is called.
imu_update() updates the state of the inertial measurement unit. This function expects to be called regularly (at 100-200 Hz) and updates the following variables:
- IMU.gx, IMU.gy, IMU.gz: rotation rate about the sensor axes in deg/sec. NOTE: these are in a right-handed coordinate frame.
- IMU.ax, IMU.ay, IMU.az: linear acceleration along the sensor axes in g
- IMU.roll, IMU.pitch, IMU.yaw: orientation in degrees (note that we will need to calibrate our magnetometer for this to work properly)
Note that IMU is a global variable defined in ImuUtils. You do not need to define it yourself.

Component 1: Hardware and Circuit

If your craft isn't balanced yet, it is now time to do this.

Inertial Measurement Unit

The IMU is a MPU-9250. Mount the Inertial Measurement (IMU) on the mast that we provide. The advantage of the mast is that your sensor will be less subject to magnetic interference from the hovercraft motors and wires, as well as sources buried in the floor. Make sure that your mast is intact and be gentle with it (don't crush it and don't grab your hovercraft by it).

Connect the IMU to your circuit. The pins are:

BLACK Ground
+3.3V power: connect to the 3.3V supplied by the Teensy
SDA: connect to SDA0 of the Teensy (Arduino pin 18)
SCL: connect to SCL0 of the Teensy (Arduino pin 19)

Component 2: Software

Copy the functions that you developed in project 6 into your current project.
Implement a new PeriodicAction (called imu_task) that executes once per 5 ms The associated imu_step() function should:
- Call imu_update().
Implement a new finite state machine in fsm_step(). This state machine will:
1. Wait for the switch to be pressed.
2. Spin up the central fan.
3. Wait in this state for 30 seconds.
4. Turn off the central fan.
5. Return to waiting for the switch.
Implement a new PeriodicAction, called pd_task, that executes once per 10 ms. The associated pd_step() function will implement a damping rotation controller. Specifically:
```
float fx = 0.0;
float fy = 0.0;
float torque = Kd * IMU.gz;   // gz = gyro about the Z axis (right-handed coord frame)
set_hovercraft_forces(fx, fy, torque);
       
```
Implement a new PeriodicAction, called report_task, that executes once per second. The associated report_step() function will print out the current rotation rate (IMU.gz).
Add each of your tasks to your loop() function.

Component 3: Testing

Perform initial testing while holding the lip of the Hovercraft with two hands (I recommend not sticking fingers in the fans).
Start with a conservative Kd (i.e., a small value).
Slowly increase the gain until the craft resists the rotations.
At this point, you can place the craft on the floor (or a table, if you are careful).
If you spin your craft, then the craft should respond by slowing down the rotation quickly (a fast initial rotation should be damped out in about one second).
If the craft tends to oscillate while on the ground, then decrease your Kd.
If the craft drifts laterally a lot while it is damping out rotations, then you need to revisit your negative_gain parameters.

What to Hand In

All components of the project are due by Tuesday, April 13th at 5:00 pm

Demonstration/Code Review: All group members must be present. The demonstration must be completed by Friday, April 16th.
Check in the following to your project 7 area of Gradescope:
- Documented code: See the project 1 specification for detailed documentation requirements.
Personal report: Catme will request that you fill out a survey about the project. These must be completed by April 16th in order to receive credit for the project.

Grading

Project lead credit:

Each person must be the primary integrator of circuits and code for two projects over the course of the semester.

For a successful project, we expect:

A properly configured circuit
- IMU is properly connected to your processor
Properly written software
- imu_step()
- pd_step()
- report_step()
- Finite State Machine implementation
Properly documented code
- Project-level documentation at the top of the ino file: name and group number, date and project number
- Function-level documentation above the function definition. Include an abstract description of what the function does; a list of the names, types and units associated with each parameter and return value; and the effects that the function has on the processor or connected components.
- In-line documentation inside of functions: individual lines or small groups of lines have an English description that describes logically what the code is doing

andrewhfagg -- gmail.com

Last modified: Sat Mar 27 15:29:40 2021