Position and Scan Control Rover

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Introduction

Objective

The functional concept of the rover is to perform CT scanning of a log by traversing alongside it in a parallel direction. While the final rendition of the rover within the scope of this capstone project will not house an x-ray producing device (for safety reasons), the positional and navigational expectations will be implemented. To achieve these expectations, the rover will house the following components for positional and navigational capabilities:

• Inertial Measurement Unit (IMU)
• GPS
• Ultrasonic Sensor
• Processor
• Microcontroller

Discussion

The figure below illustrates the ROS computation architecture which shows how the robot's firmware will function. For a quick refresher on ROS concepts, refer here. There are three parts of this architecture:

• Navigation and Communication System
• Motor Control System
• Localization System

Focusing on the IMU's role in the Localization System, the rover's acceleration, angular velocity, and linear velocity can be obtained using the device. PhidgetSpatial Precision 3/3/3 High Precision was selected because of its readily available API and company firmware support. The IMU sensor is connected to a ROS node named "IMU_node", which advertises the relevant imu data to a topic named "/imu_data".

Because the Phidget C++ API is not implemented in ROS, a driver is required. The phidgets_imu package (phidgets_imu_node) contains the required drivers to display the raw linear acceleration and angular velocity in the topic, /imu/data_raw. To fuse the angular and linear accelerations into orientation information, the imu_filter_madgwick package (/imu_filter_node) is used, which in turn publishes the fuse data on the imu/data topic.

ROS contains a native simulation tool made for teaching ROS and ROS packages that is represented by a turtle in the x-y plane. The node, /imu_node, is used to relay the positional information containing linear and angular velocity from imu/data to the turtle simulation.

Demonstration of the imu's firmware architecture is presented below, where performing yaw rotations of the imu will cause the turtle in the simulation to turn accordingly:

Conclusion

This project is still ongoing and therefore inconclusive.

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Blinking Christmas Sweater

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Results

The resulting sweaters have LEDs mounted on them that flash at a constant frequency and duration. Below is a slideshow of the three sweaters made in 2015, 2016, and 2017 respectively. The slide shows the progression and increasing "finesse" of the sweater's electronics, where in both 2015 and 2016, a single-sided prototype board was used to house the circuit. In 2017, I opted to create my own custom PCB using Altium Designer in order improve the circuit's durability, appearance, and size. For a video demonstration of blinking effects, refer to the end of this portfolio page.

Note: Unfortunately, the 2018 sweater edition was not created due to other engagements during the holidays.

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Design

The blinking effect is achieved using a LM555 timer operating in astable mode, which allows the IC to generate a square wave output. In brief, the frequency of this wave is determined by two resistors (R1, R2) and a capactor (C1). Based on LM555 datasheet, the equations below dictate the duty cycle of the squave wave:
$$t_{on} = 0.693 \cdot C_1 \cdot (R_1 + R_2)$$ $$t_{off} = 0.693 \cdot C_1 \cdot R_2$$ $$T = t_{on} + t_{off} = 0.693 \cdot (R_1 + 2R_2) \cdot C_1$$

The respective values of the passive components were chosen below based on component availability:
$$C_1 = 220uF$$ $$R_1 = 1kΩ$$ $$R_2 = 4.7kΩ$$
This results in the following characteristics of the square wave function: $$t_{on} = 0.869ms$$ $$t_{off} = 0.713ms$$ $$D_{on} = 0.55$$

The figures below show the progression of the PCB from layout placement to component population. Top left: board layout; top right: 3D model; bottom left: manufactured PCB; bottom right: populated board.

PCBs were manufactured using OSH Park.

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Video Demonstration

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