P16241: Autonomous People Mover Phase 3
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Preliminary Detailed Design

Table of Contents

Team Vision for Preliminary Detailed Design Phase

Originally, our team planned on focusing on path following and obstacle detection during this phase, however, due to some scope changes of the previous team, we decided to take a step back and look into tasks originally in Phase II's scope.

Prototyping, Engineering Analysis, Simulation

Vehicle Simulation

A MATLAB simulation was developed in order to determine cart characteristics such as cart position, steering angle, and lateral and longitudinal velocity over time when going from one point to another.

This three degrees of freedom model was developed using the state spaced equations seen below:

This model was drawn from “Optimal Vehicle Path Generator Using Optimization Methods” by Peeroon Ramanata. Virginia Tech, April 1998

Website: https://vtechworks.lib.vt.edu/handle/10919/36615

Then, a differential equation was derived in order to adjust steering angle based on position and velocity relative to a GPS way point. The equation can be seen below:

In order to achieve the outputs seen below, many inputs are needed. These inputs are GPS way points, Longitudinal tire force, initial conditions, and certain cart properties. Among the initial conditions are velocity, starting point, steering angle, and turning rate. As for the cart properties, they are center of gravity, weight distribution, moment of inertia, mass, friction coefficient, track width, and tire cornering stiffness.

The algorithm attempts to reach the next point by maintaining the same turning radius between two points.

Furthermore, oscillations are avoided by careful selection of waypoints

Once the cart location is within a specified proximity of the the current way point, the algorithm proceeds to the next way point.

Overall, this simulation will be used to predict the steering angle needed over time to get from one point to another. This can help greatly with programming the steering subsystem in order to smoothly steer around the course.

LiDAR Mounting Analysis

When looking at mounting the LiDAR, three different locations were looked into. These locations can be seen below along with their corresponding detection ranges.

Aside from the pictures seen above, a top angle was looked at to determine the regions that the LiDAR could see around the cart. The pictures for this study can be seen below for the LiDAR mounted right above the bumper and right above the dashboard.

Ultrasonics Analysis

The ultrasonics were also looked into to determine what their vision was when mounted along the front bumper. Data on this can be seen below:

Drawings, Schematics, Flow Charts, Simulations

LiDAR Mount

Aside from the location of the LiDAR, a mount was designed to actually connect it to the cart. The drawing for this mount can be seen below. It is bolted to the supports for the roof and allows the ability of the LiDAR to be tilted to multiple angles.

Mechanical Emergency Stop

Another item that was looked at during this phase was an emergency stop. The team would like to have the most fail-safe emergency stop available for the cart in case of any emergencies that might come about. The design images for the mechanical emergency stop can be seen below. This design consists of a gas spring that would be installed underneath the floor.This spring would push on the linkage between the pedal and brake lines when it is released. Additionally, the release control button can be activated by a solenoid.

Electrical Emergency Stop

Apart from the mechanical emergency stop, the team also created an electrical e-stop to cut power to the motor and electronics whilst actuating the brake in order to fully stop the vehicle.

Bill of Material (BOM)

A new GPS was purchased during this phase. The GPS is a SkyTraq S1315F8-RAW with RTK capability. Additionally, this GPS has an accuracy of ten centimeters while only costing $25

For more information, the data sheet can be seen here

Test Plans

Also during this phase, the team completed test plans for all of the engineering metrics. These can be seen here

Design and Flowcharts

A high-level software block diagram was created in order to understand how each of the different software functions fit in with each other. The diagram can be seen below:

Risk Assessment

The team's risk register was updated and a snapshot of it can be seen below along with the link to the actual document

Corresponding Document: Risk Register

Design Review Materials

Preliminary Detailed Design Presentation

Plans for next phase

The plans for the next phase can be seen in the snapshots of the schedule below:

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