Tank project

Bill of materials

The table below shows the electrical components used for the project. Prices and links are updated to January 2017.

Components description

Tank

The tank was bought from a Chinese company (SmartArduino). It’s a kit that includes all the components needed for building the tank body. The delivery time of the components is around 4 weeks.

The kit includes:

• Motors + motor cables
• Aluminium body
• Wheels and tracks
• Motor controller (not used in this project)

Spare motor

Considering the long lead time from SmartArduino, a spare motor was bought. The only one available comes with a wheel included.

The main characteristics of the motor are listed in the table below.

The motor is equipped with a hall effect encoder. The encoder has a resolution of 360° (every 360° it provides a growing and a lowering signal).

Arduino board

Arduino is an open-source electronics platform based on easy-to-use hardware and software. Arduino boards are able to read inputs (e.g. a light on a sensor, the signal of a button) and turn it into an output (e.g. activating a motor or turning on an LED) depending on the settings done by the user. You can tell your board what to do by loading a set of instructions to the microcontroller (ATmega 328P) on the board. This is done by using the Arduino programming language and the Arduino Software (IDE).

Documentation is available on Arduino website (https://www.arduino.cc/) and on the web (see YouTube tutorials).

Arduino project created different boards. For this project Arduino UNO board was used, but most of Arduino boards should work.

Arduino board has various ports:

• Digital ports (from 2 to 13 – see Figure 4.5): they are divided in 2 different categories:
  • nly digital (2, 4, 7, 8, 12, 13 in Figure 4.5): they can read a digital input and create a digital output
  • Digital + PWM (3, 5, 6, 9, 10, 11 in Figure 4.5): they can read a digital input, create a digital output, and create a PMW (pulse width modulation) output
• Analog In ports: they can read an analog input
• Power ports: they include:
  • GND ports: they connect the ground to Arduino board
  • 5V: it provides a voltage of 5 volts
  • 3.3V: it provides a voltage of 3.3 volts

Motor drive board

The motor drive board (also simply called motor controller) is a board which responds to the following functions:

• Receives signals from the Arduino board
• Receives power from the power supply
• Based on the Arduino signals, provides the motors with a defined voltage

The board acts as a “middle interface” between the Arduino and the motor. This is because the motors need to be supplied by an amount of current that Arduino cannot handle. So Arduino provides the signal, while the motor drive board “joins” the signal with the power.

The board can accept a maximum power of 600 mA per channel.

The main component of the board is the chip L293D (from ST Microelectronics). A datasheet can be downloaded from this link: https://www.arduino.cc/documents/datasheets/H-bridge_motor_driver.PDF

The motor drive board includes some other components (that will not be described here), but its main purpose is to allow the user to have a physical connection to the L293D chip.

The chip includes a double H bridge, which is a standard way of controlling DC motors. Thanks to the dual H bridge, this chip can control 2 motors at the same time. The L293D has 16 ports, which are connected to the motor drive shield jumpers. The connections are shown in Figure 4.7.

NOTE: the connections shown in the image show the connections that are internal to the board. The image purpose is to help the reader understand how the board works.

The meaning of the symbols of the figure is explained in the following table.

Terminal strip connector

This is an easy way of connecting two cables. It is an alternative to brass welding. The cables are inserted in the two sides of the jumper and clamped with the integrated screws. This guarantees electrical continuity between the two cables.

Power supply

The selected power supply provides a voltage of 9V (required from the motor) and a maximum current of 3A. This is higher than the maximum current accepted by the motor controller (2 x 500 mA = 1 A).

The terminal of the power supply was cut to insert the two wires directly into the motor controller.

Jumper connectors

They are an easy way of connecting boards. They can be used, for example, to connect Arduino board to the Motor drive board. They can only accept a low current, so they must only be used for providing signal (not power).

Fuses

A fuse is an electrical safety device that provides overcurrent protection of an electrical circuit. Its essential component is a metal wire that melts when too much current flows through it, thereby interrupting the current. It is a sacrificial device and once a fuse has operated it must be replaced. The fuse is contained inside the fuse holder. The tank uses 500 mA fuses, which provide protection to the Motor drive board (whose maximum current is 600 mA per channel).

Cable (20 AWG)

A 20 AWG cable is able to transfer a current of 1.5A, so it’s right for transferring current (and power) between the motor drive board and the motors.

This chapter describes how the previously described components are wired. All the different wiring steps will be shown at first.

Power supply

Power supply cord is connected as follows:

• Ground cable (black) is connected to GND port
• Power cable (red) is connected to VIN port

Motor drive board to motor

Motor drive board is connected to the motors using the 20 AWG cables. Fuses are inserted to guarantee the safety of the motor drive board.

The connection to the motor pins needs to be done using the positions shown in the following image.

Arduino to Motor drive board

The motor drive board is connected with the Arduino using the Jumper cables. Each cable transfers a signal from the Arduino to the Drive board.

For example, if Arduino pin number 3 goes high, the port EN1 of the board is high. This enables the activation of the motor 1 (see chapter "Motor drive board").

Sensors power + sensor signal

The speed sensors of the two motors are powered by the Arduino 5V power supply (see grey and yellow lines in the following image). The same supply also powers the motor drive board chip. This is possible because the sensors need a very small current to be powered.

The signals from the two sensors are returned back to the Arduino with 2 single cables (see black and blue lines in the following image).

Each sensor also provides a second signal (see light blue and green lines in the following image). These signals could detect the direction of the motors, but are not connected for this application.

Arduino to PC

Arduino is connected to the PC using the USB connector that is provided in the package. This connection provides:

• The 5V power supply to the Arduino
• The signals between the Arduino and the PC (serial communication)

Overall tank connections

The combination of the connections described in the previous chapters is shown here.

The structure which supports the tank was built using the following components:

• Plasterboard (available at Homebase)
• Wood bar
• Black tape
• Wide head steel nails
• 5 mm wood dowel

The following tools are suggested:

• Screwdriver
• Jigsaw

Manufacturing and assembly drawings are shown in appendix.

The approach to construction should be as follows:

1. Cut the plasterboard to length following the components’ drawings
2. Cut the wood bar to length following the components’ drawings
3. Drill the holes in the plasterboard
4. Drill the holes in the feet using the holes in the plasterboard as a reference
5. Apply some tape over the holes in the plasterboard to increase strength
6. Assemble the components using nails and dowels
7. Position the three blocks close to each other

A support for the tank has been created and screwed to the tank bottom panel, as shown in the following figure. The height of this support should be adjusted to keep the tank as close as possible to the tank top panel. No drawings are available for this support.

The software for controlling the tank movement is divided into two programming languages:

• Matlab: controls the events which decide when a stimulus should be performed, including:
  • Stimulus onset
  • Stimulus speed
  • Stimulus direction
• Arduino: following the indications given by Matlab program, controls the movements that the motors need to follow during a single stimulation trial. This is done by directly controlling the motor drive board status.

The two programs communicate through a serial communication, which is performed used the USB cable that connects Arduino to the PC. The Arduino then communicates with the Motor drive board for the motor activation using simple 0 to 5V signals. A scheme of the software workflow is shown below.

After the start, an handshake procedure is performed to verify the communication between Matlab and Arduino. Matlab then sends a series of command to Arduino defining the settings of the next stimulus (speed, direction and motor activation). Arduino receives the signals and delivers them to the motor drive board, which activates the motors with the required settings.

While the motors are running, the signals from the encoder are passed to Arduino, which elaborates them and send the time and position readings back to Matlab. This procedure runs continuously while the motors are running.

When the running time has elapsed, Arduino stops the motors and sends a stop signal to Matlab. If Matlab requires a new run to be executed, the procedure is re-started. Otherwise the software stops and waits for a new start indication from the user.

The software for the activation of the tank is recorded and described in the appendix.

Main program

This program sets the functions of the tank. It provides the following actions:

• Sets the communication with Arduino doing the handshake (calling “SetCommunication” – see chapter 2.2)
• Translates the required tank settings into commands that can be sent to Arduino via serial communication (calling “MotorSetting” – see chapter 2.3)
• Sends to Arduino a series of letters (through serial communication) that include the commands for:
  • The setting of the direction of motor A and B (e.g. the letter “a” means that the motor A will move forward)
  • The setting of the speed of motor A and B (e.g. the letter “t” means that the motor B will run at medium speed)
  • The activation of motor A and/or B (e.g. the letter “f” means that the motor B only will start)
• Executes the loop where the motors are activated. The loop records the communications that arrive from Arduino as follows:
  • Read and record the time of the reading
  • Read and record the instant position of motor A and B
  • Reading is stopped when Arduino sends the value -1, which means that the run of the motor is finished
• Calculates and save the speed profiles of the two motors starting from the time and position data provided by Arduino
• Calculates and save some important values for each motor and each run, like:
  • Average speed
  • Motor activation time (for each motor + difference between motors)

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% Activate communication between Matlab and Arduino %%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

SetCommunication;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% Start the experiment %%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% Logical variable for trials while loop
P.allTrialsDoneBool = 0;
% Trials counter (max = S.nTrials)
TrialNr = 1;

%Initialise vector for all readings
S.ReadInterval = 2;
S.TimeTot = cell(S.nTrials,1);
S.SpeedATot = cell(S.nTrials,1);
S.SpeedAMeanTot = cell(S.nTrials,1);
S.SpeedAStdTot = cell(S.nTrials,1);
S.SpeedBTot = cell(S.nTrials,1);
S.SpeedBMeanTot = cell(S.nTrials,1);
S.SpeedBStdTot = cell(S.nTrials,1);
S.SpeedMeanDiffTot = cell(S.nTrials,1);
S.MotAStopTot = cell(S.nTrials,1);
S.MotBStopTot = cell(S.nTrials,1);
S.MotStopDiffTot = cell(S.nTrials,1);
S.PositionATot = cell(S.nTrials,1);
S.PositionBTot = cell(S.nTrials,1);

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% Start the trials while loop %%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

while ~P.allTrialsDoneBool
    
    S.Time = [];      %time readings
    S.SpeedA = [];    %motor A speed 
    S.SpeedB = [];    %motor B speed 
    S.PositionA = []; %motor A position (= encoder revolutions) readings
    S.PositionB = []; %motor B position (= encoder revolutions) readings
    m=0;		    %tell Matlab stimulus is completed (0 = no; -1 = yes)
    
    % Serial communication of direction and activation to Arduino
    [DirA, DirB, SetSpeedA, SetSpeedB, MotActive] =  
    MotorSetting(S.RunDirA(TrialNr), S.RunDirB(TrialNr),...
    S.RunSpeedA(TrialNr), S.RunSpeedB(TrialNr), S.RunMotActiveA(TrialNr), 
    S.RunMotActiveB(TrialNr));

    fprintf(arduino,DirA);
    fprintf(arduino,DirB);
    fprintf(arduino,SetSpeedA);
    fprintf(arduino,SetSpeedB);
    fprintf(arduino,MotActive);
    
    % Record all the data sent by Arduino
    while (m~=-1)
        
        % Time data
        m = fscanf(arduino,'%f');
        if (m == -1)
            break;
        elseif (m > -1)
            S.Time = [S.Time,m];
        end
        
        % PositionA data
        m = fscanf(arduino,'%f');
        if (m == -1)
            break;
        elseif (m > -1)
            S.PositionA = [S.PositionA,m];
        end
        
        % PositionB data
        m = fscanf(arduino,'%f');
        if (m == -1)
            break;
        elseif (m > -1)
            S.PositionB = [S.PositionB,m];
        end
    end
    
        for i = 1:length(S.Time)
        if i < length(S.Time)-S.ReadInterval
            PosATemp = S.PositionA(i+S.ReadInterval);
            PosBTemp = S.PositionB(i+S.ReadInterval);
            TimeTemp = S.Time(i+S.ReadInterval);
        else
            PosATemp = S.PositionA(length(S.Time));
            PosBTemp = S.PositionB(length(S.Time));
            TimeTemp = S.Time(i) + 20;
        end
        
        S.SpeedA(i) = (PosATemp-S.PositionA(i))...
            /(TimeTemp-S.Time(i))*1000; % [rev/sec]
        S.SpeedB(i) = (PosBTemp-S.PositionB(i))...
            /(TimeTemp-S.Time(i))*1000; % [rev/sec]
    end
    
    S.SpeedAMean = mean(S.SpeedA);
    S.SpeedAStd = std(S.SpeedA);
    S.SpeedBMean = mean(S.SpeedB);
    S.SpeedBStd = std(S.SpeedB);
    if S.SpeedAMean ~= 0 && S.SpeedBMean ~= 0
        S.SpeedMeanDiff = S.SpeedAMean-S.SpeedBMean;
    else
        S.SpeedMeanDiff = NaN;
    end
 
    if S.RunMotActiveA(TrialNr) == 1
        if mod(length(S.SpeedA),2)==0
            S.MotAStop = S.Time(find(S.SpeedA(length(S.SpeedA)/2:end)==0, 1)+length(S.SpeedA)/2-1);
        else
            S.MotAStop = S.Time(find(S.SpeedA(median(1:length(S.SpeedA)):end)==0, 1)+median(1:length(S.SpeedA))-1);
        end
    else
        S.MotAStop = NaN;
    end
    
    if S.RunMotActiveB(TrialNr) == 1
        if mod(length(S.SpeedB),2)==0
            S.MotBStop = S.Time(find(S.SpeedB(length(S.SpeedB)/2:end)==0, 1)+length(S.SpeedB)/2-1);
        else
            S.MotBStop = S.Time(find(S.SpeedB(median(1:length(S.SpeedB)):end)==0, 1)+median(1:length(S.SpeedB))-1);
        end
    else
        S.MotBStop = NaN;
    end
    
    if S.MotAStop ~= 0 && S.MotBStop ~= 0
        S.MotStopDiff = S.MotAStop-S.MotBStop;
    else
        S.MotStopDiff = NaN;
    end
    
    %Save read data
    S.TimeTot{TrialNr} = S.Time;
    S.SpeedATot{TrialNr} = S.SpeedA;
    S.SpeedAMeanTot{TrialNr} = S.SpeedAMean;
    S.SpeedAStdTot{TrialNr} = S.SpeedAStd;
    S.SpeedBTot{TrialNr} = S.SpeedB;
    S.SpeedBMeanTot{TrialNr} = S.SpeedBMean;
    S.SpeedBStdTot{TrialNr} = S.SpeedBStd;
    S.SpeedMeanDiffTot{TrialNr} = S.SpeedMeanDiff;
    S.MotAStopTot{TrialNr} = S.MotAStop;
    S.MotBStopTot{TrialNr} = S.MotBStop;
    S.MotStopDiffTot{TrialNr} = S.MotStopDiff;
    S.PositionATot{TrialNr} = S.PositionA;
    S.PositionBTot{TrialNr} = S.PositionB;

Communication setup

This script sets the communication protocol between Arduino and Matlab. The communication is done through serial communication, whose parameters are set at the beginning of this script. Serial port name is the only parameter that needs to be changed if the program is run on a new PC (verify the Arduino COM number after connecting it to the PC, the procedure can be easily found online).
After opening the serial communication, Matlab starts to “listen” for Arduino. If Arduino sends the letter “a”, Matlab sends the letter “a” back to Arduino. This is done to confirm that the communication is working and packages of data can be sent either way through the serial port.
After the handshake is completed, a confirmation is printed on screen.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%% SET COMMUNICATION %%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% This script sets a serial communication between Arduino and Matlab
% See http://www.instructables.com/id/Arduino-and-Matlab-let-them-talk-using-serial-comm/?ALLSTEPS

% Set and open serial communication
arduino = serial('COM3');
set(arduino,'DataBits',8);
set(arduino,'StopBits',1);
set(arduino,'BaudRate',9600);
set(arduino,'Parity','none');
fopen(arduino);

% Performs an handshake between Arduino and Matlab to verify the
% communication. Waits for Arduino to send the command "a" through 
% serial, and after receiving it sends it back 
a = 'b';
while (a~='a') 
    a=fread(arduino,1,'uchar');
end
if (a=='a')
    disp('Serial read');
end
fprintf(arduino,'%c','a');

% When communication is ready prints a message on the screen
mbox = msgbox('Serial communication ready'); % uiwait(mbox);
fscanf(arduino,'%u');

Motor setting function

This function is used to “translate” the requirements of motor activation, speed and direction into commands to be sent to Arduino via serial communication. These commands are used to send the motor settings (speed, direction and activation) from Matlab to Arduino. This is needed because Matlab includes the process of defining which type of setting the motor needs to have, while Arduino physically sets the motors to execute these settings. Each command is delivered by a different letter, which is then interpreted by Arduino. This is the complete list of the commands that Matlab can send to Arduino to set the motors:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%% MOTOR SETTING %%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% This function takes Matlab direction and motor activation settings and translates them to the signal that Matlab will send to Arduino through serial communication

% ARDUINO COMMANDS:
% a = Motor A forward set
% b = Motor A backwards set
% c = Motor B forward set
% d = Motor B backwards set
% p = Motor A high speed set
% q = Motor A medium speed set
% r = Motor A low speed set
% s = Motor B high speed set
% t = Motor B medium speed set
% u = Motor B low speed set
% e = Motor A start
% f = Motor B start
% g = Motor A & B start

function [FunDirA, FunDirB, FunSpeedA, FunSpeedB, FunMotActive] = MotorSetting(RunDirA, RunDirB, RunSpeedA, RunSpeedB, RunMotActiveA, RunMotActiveB)

% Translation direction
    if RunDirA == 1
        FunDirA = 'a'; 
    else
        FunDirA = 'b';
    end
    
    if RunDirB == 1
        FunDirB = 'c'; 
    else
        FunDirB = 'd';
    end
  
% Translation speed
  if RunSpeedA == 0
    FunSpeedA = 'p'; % Motor A high speed set
  elseif RunSpeedA == 1
    FunSpeedA = 'q'; % Motor A medium speed set
  else 
    FunSpeedA = 'r'; % Motor A low speed set
  end
  
  if RunSpeedB == 0
    FunSpeedB = 's'; % Motor B high speed set
  elseif RunSpeedB == 1
    FunSpeedB = 't'; % Motor B medium speed set
  else 
    FunSpeedB = 'u'; % Motor B low speed set
  end

% Motor activation
    if RunMotActiveA == 1 && RunMotActiveB == 1
        FunMotActive = 'g'; 
    elseif RunMotActiveA == 1
        FunMotActive = 'e';
    elseif RunMotActiveB == 1
        FunMotActive = 'f';
    else
        FunMotActive = 'h';
    end
end