Scope of Project

Introduction

The border between the United States and Canada is the longest land border in the world. Most of the terrain on this border of these states is rugged, cold and occasionally muddy. This makes it difficult to monitor, unless you have the use of drones. Based on the success of land drone designs in Russia, who have a similar climate and landscape to the bordering states, a similar vehicle designed to patrol parts of the U.S. and Canadian borders would be ideal. To do this Land Drone team #5 will be taking Russia’s idea of all-terrain land drones and will apply to them the elements of data collection and GPS location. With these new adaptations we can use the land drone to report back information on the border. The Department of Homeland Security can use these drones to monitor the more treacherous parts of the border, leaving border patrol officers to focus on more important tasks.

Our immediate goal is to design an autonomous land drone vehicle that can meet the performance objectives and design constraints defined by MEE 487 Professor Michael Peterson.

Technical Approach

The main objective for the land drone design is to be able to successfully monitor the United States and Canadian border. This is, however not what our objective is. We are still in phase one of the design process where teams are given certain design constraints and expected to meet certain performance objectives. The team with the best results in the competition, theoretically, has the best design and we will further the process from there.

Constraints

The constraints for this phase of the design were made for us by Professor Michael Peterson, the capstone professor overseeing the project. The idea is that these similar constraints will ensure the best design will win. The constraints are as follows;

  • Budget – The complete budget for the project is $1400 and all materials no matter how cheap they were attained need to be notated at cost.
  • Arduino – The Arduino must be the microprocessor controlling the obstacle avoidance and GPS locator in the land drone.
  • Engine – The only engines allowed are a Stihl MS 211 chainsaw engine or a 3hp 79cc 4-stroke lawn mower engine.
  • Size – The dimensions of the land drone need no more than three feet high, three feet wide and a six feet footprint. The land drone cannot be more than 200 pounds.
  • Sound – The land drone cannot produce more than 90dB on any type of surface.
  • Speed – The land drone cannot go faster than ten mph.
  • The land drone must have a real light emitting 500 lumens and a front light emitting 700 lumens.
Performance Objectives

From the eventual tasks the land drone needs to accomplish in order to successfully monitor the border, we can deduce the performance objectives. The main performance objectives are listed below:

·       Terrain – The main reason land drones were suggested is because of the rough and                 unforgiving terrain in the northern states. If the land drone cannot cross this terrain by          traversing obstacles it is essentially  useless for its intended purpose. The biggest                 problems will be roots no more than nine inches, rocks no bigger than a foot and an             grade no steeper than 8 percent.

·      Obstacle Avoidance – Not every obstacle can be overcome, some just have to be simply             avoided. To do this an obstacle avoidance program must be implemented.

·      Water – On the course there is a possibility of crossing water at most, 2 feet deep, 50             feet wide and flowing at 3 meters per second.

·      Competition – Six GPS coordinates must have visual and acoustic data collected from                 them within a half hour. The course length is 1.2 miles.

Design Trade Offs
Based on the certain constraints and performance objectives, design tradeoffs were made to ensure optimal performance. The four main design tradeoffs made are listed below:

    Tracks or Tires?

A big initial choice is whether tires or tracks should be used. (Legs were out of the price range of this project). Tires give quicker speed because each tire is individual driven, in other words less surface friction. They are also cheaper to make with a similar suspension system because it is a single tire rather than an entire track. Tracks have a higher surface area contact giving them much more control and propulsion. They also, if designed correctly, can have a superb suspension system because of small bogy wheels between the drive wheels. Below is a chart highlighting the pros and cons of the choice. 

Table 1 - Wheels vs. Tracks


Tracks

Tires

Pros

  • Greater off-road traversing ability

  • Larger contact patch with the ground

  • Much greater maneuverability/ turning radius

  • Cheaper cost

  • Simpler suspension systems


Cons

  • More complicated suspension systems

  • Heavier weight

  • Less ability to traverse obstacles

  • Less precise maneuverability


Based on the information in Table 1 we chose tracks instead of wheels. This will give us less speed and more maintenance, but the biggest performance objective in the design is overcoming obstacles and tacks are much more efficient. 

    Drivetrain?

The drivetrain consists of the mechanical transfer of the chain saw engine into the movement of the vehicle. The two methods we considered were; 1) the chain saw engine going directly to a gearbox turning the tracks, or 2) using the chain saw engine to drive an alternator, which would power electric motors. The give and takes for our methods are highlighted in Table 2 below.

Table 2 - Drivetrain


Direct from chainsaw engine

Alternator driving electric motors

Pros

  • Cheaper cost

  • Less weight

  • Exceptionally simpler to program

  • More precise control over speed and torque

  • Flat torque-curve

Cons

  • More difficult to control gas-powered motor output autonomously

  • Complex mechanical gearbox and differential system to control tracks

  • Heavier

  • More electronics to be put in water

Based on the information in Table 2 we decided to have the chainsaw engine charge an alternator, used to run electric motors. This is a lighter setup than taking power directly from the chainsaw, and it allows our drone to have much more maneuverability, with both tracks being able to run independently.

    Chassis?

The chassis is the platform that holds the drivetrain, suspension and electrical systems in place while also adding integrity to the entire vehicle. Key points that we will include in our design are;

  • Weight to strength ratio: This is crucial because the chassis needs to have the strength to withstand the torque load from the engine while being light enough to reduce strain on the motor.

  • Size (compact and short): The dimensions are important to the design and having the drone short and compact allows a lower center of mass making the drone more stable, one of our constraints, with fewer tendencies to flip. It also allows obstacles to be traversed easier while maintaining a stable platform for the video and audio recording.

  • Ability to float: Having the drone float rather than ride on the water floor makes the design much easier to execute and is more reliable to stay on track then traversing the ever changing water floor.

    Controls?

Since we are deciding to use electric motors a method of motor control using controls must be established in order to avoid obstacles. The method we chose is a simple DC motor H bridge. An H-bridge uses transistors to change the current flowing through the motor from positive to negative, effectively changing the motor direction. Being able to change the motors direction allows the land drone to be able to spin in a literal circle so maneuverability is extremely high. Also having an H-bridge allows us to have a simple motor braking using the Arduino rather than adding a brake pad and disc.

Budget

The total budget for this experiment is $1400 so all the highest quality equipment cannot be purchased. The bulk of the expense for our land drone needs to be with in the electric motors, alternator and track system, about 70%. The remaining 30% will be spent and the controls system, chassis, battery and chainsaw engine.

Team

For our team, Land Drone #5, we have four total members; Michael Bleier, Joshua Boucher, Sarah Small and Michael Freeman. Our team is very strong with mechanical design, such as the drivetrain, tracks and chassis. The biggest problem our group will have to overcome is the controls portion. None of us are particularly proficient with circuits or schematics so designing our own original control design will certainly be tough. Our supervisors are Professor Michael Peterson and Lab director Stephan Abbadessa. Between both of the advisors and their many years of technical experience, they will be indispensable to help drive phase one of the design in the right direction. As of now there are no outside contributors for this project, but for future phases the department of homeland security and department of defense are definite possibilities.

Organization of Responsibilities

Our design team is identified as Land Drone #5. The members of the group are, Michael Bleier, Sarah Small, Joshua Boucher and Michael Freeman. For this project we decided to split up key parts to individual members and collaborating once we have an idea. The member’s responsibilities are listed below. 

 Michael BleierSarah Small  Joshua Boucher Michael Freeman

Calculations to determine needed torque for an 8% grade with roots and rocks 


 Free body diagram of forces acting upon vehicle 
 
Chassis design and weight estimation 
 
Vehicle speed and directional control (schematic) 
 

Selection of electric motors 

 

Location of center of Mass 

 

Emergency brake design 

 

Red and white flashing lights (schematic) 

 

Track design 

 

Maintaining up to date website 

 

Solidworks drawings of motors 

 

GPS location and obstacle avoidance (schematic) 

 

Solidworks drawings of track system 

 

Solidworks drawing of chassis 

 

Solidworks drawing of chassis 

 

Wiring Diagram