AME 3623: Project 5: 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 6, we will use all nine degrees-of-freedom to estimate the orientation of the hovercraft.

All components of the project are due by Friday, March 27th at 3:30 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

In your Arduino environment: in the sketch menu, select Manage Libraries / Add .Zip Library
Navigate to and select ImuUtils.zip. Click Ok
In your Arduino environment: in the sketch menu, select Manage Libraries / Add .Zip Library
Navigate to and select QuaternionFilters.zip. Click Ok
Likewise for MPU9250.zip
Likewise for PWMServo-2.1.0.zip

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

In order for your hovercraft to lift off the floor, it must be balanced. Move your circuit board into a position such that your craft is balanced front-to-back and left-to-right.

Every hovercraft should have a battery platform just behind the central fan (and it should be affixed to the hovercraft body). We have provided Velcro tape to use for affixing your battery to the platform. We recommend a large strip of "hooks" on the platform and small sections of "loops" on the batteries.

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)

Central Fan

Your central fan is hard-wired into the +11V switched power supply. This connection provides power to the fan's control circuitry and to the fan motor. In most cases, this power connection has been unplugged. You will need to plug it back in before you use the central fan (this will start the annoying beep, however).
The remaining central fan connector has two pins: ground (black) and torque magnitude (white). Connect ground to your processor's ground and the torque magnitude signal to a free PWM pin.

Component 2: Software

Copy the following function from project 1:
- void display_orientation_velocity(float velocity)
- The supporting setup() code.
Copy the functions that you developed in project 4 into your current project.

Add the following code to the top of your program

PWMServo fan;  // create servo object to control the fan
const int CENTRAL_FAN_PWM = ???;
     
void fan_setup() {
     fan.attach(CENTRAL_FAN_PWM);  // attaches the fan to specified
                                   //   Arduino pin to the object
     delay(100);
     fan.write(20);  // write low throttle
     delay(3000);
}

Make sure to call this new function from setup()

Implement a new PeriodicAction (called imu_task) that executes once per 5 ms The associated imu_step() function should:
- Call imu_update().
- Display the rotation velocity of the craft.
Implement the following function:
void set_forces_and_torques(float fx, float fy, float torque)
This function accepts as input desired forces to be applied to hovercraft chassis, translates these desired forces into an appropriate thrust level for each of the lateral fans, and changes the thrust state of these fans. Note that the precise units of these forces are not really known (don't worry, the units will "wash away" once we introduce our control gains).
Implement a new finite state machine in fsm_step(). This state machine will:
1. Wait for the switch to be pressed.
2. Set the central fan to a 25-40% duty cycle (use the smallest level that brings the craft off the ground).
  You can set the duty cycle of the central fan using:
  fan.write(duty)
  where the duty parameter is a value between 0 and 255 (corresponding to zero to 100% duty cycle)
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 = Kv * IMU.gz;   // gz = gyro about the Z axis (right-handed coord frame)
set_forces_and_torques(fx, fy, torque);

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 Kv (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 the craft tends to oscillate while on the ground, then decrease your Kv.

What to Hand In

All components of the project are due by Friday, March 27th at 3:30 pm

Demonstration/Code Review: All group members must be present. Given time, this can be done during class. The demonstration must be completed by Tuesday, March 31st.
Check in the following to your project 5 area of your Dropbox:
- 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 Tuesday, March 31st in order to receive credit for the project.

Grading

Personal programming credit:

Each person must accumulate at least three personal programming credits over the course of the semester.
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."

Group grade distribution:

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: Tue Mar 31 14:15:59 2020