Unmanned Ground Vehicle (UGV)

 

Tech Stack

 

 

Budget

 

 

Technical Drawings

 

Mobile Platform Base

·         The platform bases are designed like a pegboard to make the UGV more modular, and they’re manufactured from acrylic using a laser cutter

o   This design facilitates designing and fastening peripheral mounts/attachments and flexibly position them as needed

o   The platform bases are manufactured from acrylic for the material’s low conductivity and ability to withstand heat, thereby reducing unintended influence on electronic components

o   Laser cutting the design onto an acrylic sheet allowed for consistent and accurate cuts

·         Laser Cut at Maker FX Maker Space on Boss Laser LS-1630

 

Raspberry Pi 4 Model B Mounting Block

·         3D Printed at Orange County Library – Melrose Center Maker Space on Bambu Lab A1 printer

 

Breadboard Mounting Plate

·         Breadboard dimensions: 3.25” X 2.125”

·         Breadboard comes with adhesive sheet to adhere to mounting plate

·         Laser Cut at Maker FX Maker Space on Boss Laser LS-1630

 

6V Battery Mounting Block

·         Rev A:

o   Fastener head clearance too tight

o   It is difficult to remove battery box from mounting block without flipping upside down

§  Needs space to fully grip battery box for removal from mounting block

·         3D Printed at Orange County Library – Melrose Center Maker Space on Bambu Lab A1 printer

 

DC ‘TT’ Motor

·         DC ‘TT’ Motor assembly file from GrabCAD, as indicated in drawing notes

·         Technical drawing by me

 

DC ‘TT’ Motor Mounting Block

·         Only the right drive motor mount was modeled, so the model was mirrored in the Bambu Studio slicing software when 3D printed to produce the left drive motor mount

·         3D Printed at Orange County Library – Melrose Center Maker Space on Bambu Lab A1 printer

 

L298N Mounting Plate

·         Laser Cut at Maker FX Maker Space on Boss Laser LS-1630

 

SG90 Servo Motor Mounting Block

·         Rev A

o   The mounting block is designed to fasten to the servo motor via two M2.5x5+6mm standoffs, so the print will be 5mm too short for a motor to sit directly in the saddle without standoffs

·         Rev B

o   Added missing width dimension in drawing

o   Taller standoff supports clearing fastener heads and motor wires’ bend radius

o   Narrower standoff supports improving servo fit in mount saddle

o   Standoff support thread holes’ diameter increased from 2.1mm to 2.2mm

o   Use M2x5+3mm standoffs to fasten servo motor to mount

·         3D Printed at Orange County Library – Melrose Center Maker Space on Bambu Lab A1 printer

 

 

Pictures of Manufactured and Assembled UGV

 

 

Mechanical

 

DC Gear Box Motor – DC ‘TT’ Motor

 

Technical Specifications

 

 

·         Voltage à Speed

·         Current à Torque

 

·         Gear Ratio: Motor shaft turns 48 times for every 1 turn of the output shaft (wheel)

 

·         Stall Torque: Maximum rotational force a motor can produce when the shaft is prevented from turning, resulting in zero rotational speed

o   When a motor is at stall torque, it draws maximum current which can lead to overhearing and damage if stalled for too long

o   Stall current can be measured by connecting an ammeter in series with the motor, physically fixing the motor shaft to prevent it from turning, and applying voltage to the motor.  The ammeter reading when the motor is physically stalled is the stall current.

 

·         Constant Voltage: Torque is inversely proportional to Rotational Speed

o   Stall torque occurs when rotational speed = 0, so where the torque-speed curve intersects the y-axis

o   Zero-torque occurs when rotational speed = maximum, also known as the no-load speed

 

 

·         Determine the motor’s torque and a given speed using the equation of a line to define the torque-speed curve

 

 

SG90 Servo Motor

 

Source: Circuit Geeks

 

·         Position-controlled motor that can be useful to precisely control the position of robotics

·      Rotation range:

o   No continuous motor movement

 

·         Disadvantages:

o   Slower movements

o   Lower output power than other motor types

 

Source: Circuit Geeks

 

·         Components:

o   DC Motor

o   Gearbox: Reduce speed and increase torque; drives position of the output shaft, measured in degrees

o   Potentiometer: Monitor the position of the output shaft and deliver position feedback

o   Control Circuit: Interprets the input signal to determine the position of the arm and how much movement is required

 

Source: Circuit Geeks

 

·         Consists of 3 wires (wire colors may vary by motor):

o   VCC (5V): Supplies electric current to motor

§  Know how much power the use-case requires to know how much power / current it will need to pull from its power source

·         Different motors and use-cases will have different requirements depending on the size and workload

§  Power supply rating should be greater than the stall current of the servo, per servo connected to the power supply

·     

·         Consider the PCA9685 for controlling multiple servo motors with one microcontroller

o   GND

o     Signal (PWM): Delivers control signal to motor (degrees, )

 

·         Servo motors are driven by indicating the angle at which the output shaft should be positioned, expressed in degrees

o   Signal delivered as PWM

§  Pulse width determines servo arm position

Source: Circuit Geeks

 

 

Electrical / Electronics

 

Raspberry Pi 4 Model B

 

 

L298N Motor Driver

·         The DC motors are rated for a voltage that exceeds what a microcontroller outputs

·         A motor driver provides the motors with an external power source that meets the motor’s specifications but receives logic signals from the connected microcontroller

·         The L298N microcontroller has H-bridge and Pulse Width Modulation (PWM) capability, controlling the motor’s output effort (i.e. rotation speed) and direction

 

 

·         H-Bridge: Uses Boolean signals to control the direction that the motor spins (clockwise vs. counterclockwise)

o   The Boolean signal defines the motor’s polarity by changing the direction that the current flows through a motor

o   Switching the polarity switches between a clockwise and counterclockwise motor rotation

 

 

 

·         Pulse Width Modulation (PWM): Commands a percentage to define how much of a motor’s total available ‘effort’ (Duty Cycle) to output as a digital signal

o   The power delivered to the motor is not actually reduced to a percentage of the total motor spec

o   Instead, the power supplied continually flips between a ‘low’ and ‘high’ state to simulate a variable voltage that’s bound between the min and max operating speed

§  This state flipping is not perceivable to the human eye

 

 

 

·         The diagram below shows how the L298N motor driver is connected to the DC motors and the microcontroller logic pins

 

 

 

Ultra Wideband (UWB)

·         Ultra-Wideband (UWB) is a high-precision, short-range wireless radio technology used for accurate, low-power device localization at short distances

o   Devices send multiple short radio pulses over a wide frequency band and measure the time it takes for signals to travel between one another (Time of Flight, ToF) to determine their distance and position

o   Large bandwidth provides high data rates and stability to reduce interference while enabling precise positioning

§  Ideal for indoor positioning and navigation

 

 

·         These peripherals use Serial Peripheral Interface (SPI), a synchronous serial communication for short-distance wired communication

o   See Communication Protocols: SPI in Tech Notebook

 

ESP32 UWB Pro with DW1000

 

 

ESP32-WROVER Pin Layout (Top View)

Source: Makerfabs ESP32 UWB with DW1000 Documentation

 

 

ESP32 Pin Definitions

Source: Makerfabs ESP32 UWB with DW1000 Documentation

 

 

Algorithms

 

·         All algorithms implemented in this UGV are documented in the Tech Notes section of my digital notebook!

o   Localization: Trilateration

o   Path Planning: A* Path Planning

 

 

Software

 

·         All code implemented in this UGV is publicly available on my github!

o   Localization

o   Path Planning

o   L298N Motor Driver Demo

o   SG90 Servo Motors

Helpful Links

·         H-Bridges

·         Ultra Wideband Sensors

·         Servo Motors

·         Makerfabs ESP32 UWB with DW1000