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3D Printed Arduino + Bluetooth Tank

3D Printed RC Tank

I’ve been working on a new remote controlled tank in my spare time. My goal with this project is to make a cheap, printable RC tank kit. This post goes back and forth between talking about the tank, and a basic tutorial on how the components and code work together.

Currently it’s a working prototype. The tank uses an Arduino Nano clone (ATmega328) as the primary board. An L298n H-Bridge is used to control the left and right motors independently, allowing it to quickly turn or revese. It uses the HC-06 Bluetooth module to receive commands. The power comes from two 18650 batteries that are connected in series.

3D Printed RC Tank

 

Hardware:

I purchased the majority of the hardware from Aliexpress, because it’s so cheap. The links below are to the stores that I used, but you can find the same parts on many websites other than Aliexpress.

  • Arduino Nano V3 Clone ( AtMega328p ) – Link
  • L298n H-Bridge Motor Controller – Link
  • HC-06 Bluetooth Module – Link
  • 2x DC Motor + 64:1 Gearbox – Link
  • 2x 18650 Battery – I took mine from an old laptop, wired them in series for 7V+
  • 1x 500mA Polyfuse – Optional, put between power source and VIN

 

I salvaged some steel weights from an old set of window blinds, and super-glued them to the base to add some weight.

Tank Front View
Tank Front View

 

Frame:

The frame of the tank was printed as a solid piece. There are four mounting spots for wheels. The two at the front are designed so that small bearings will slot into them, so that the front wheels spin freely. The other two of the mounts are designed to hold the gearbox motors. I made a T-shape in the center of the frame so that I can mount a breadboard on top of the frame. The frame design leaves much to be desired, it’s much too thin and flexible.

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The front and rear wheels have teeth that are spaced out, so that they catch on the inside of the cable-chain tracks. The teeth are tapered slightly to keep the tracks aligned, and there is a guard on the front wheels to ensure that they stay on. The battery holder has holes in the sides and bottom so that wires can pass through. Screws hold the wheels in place.

RC Tank Sideview
RC Tank Sideview

 

Schematic:

The Arduino and L298N are powered using two 18650 batteries. These are fairly common rechargeable batteries, with an output around 3.7V. I wired my batteries in series. My schematic says 7.2V, that’s a typo, it’s really 7.4V+. I use the VIN pin on the Arduino Nano to power the chip.

The 5V output on the Arduino powers the HC-06 module. Make sure that you’re using an HC-06 module with a breakout board like mine, so that it is 5V tolerant. This is because the raw HC-06 chip is NOT 5V tolerant.

Pins 2 and 3 are connected to the HC-06, and pins 4 through 7 are connected to the L298N. On the L298N, pins ENA and ENB are used for PWM control of the outputs, so that you can achieve finer speed control. I don’t utilize these, so they are set high.

Schematic

 

Code:

There are only two main components to control other than the Arduino itself, they are the HC-06 and the L298n. The HC-06 is going to receive data from an external source, and then pass it to the Arduino. Then the Arduino will make a decision, and send signals to the L298N to turn on the motors.

There is a link at the bottom to download the full code, or read through and copy/paste the example blocks.

 

Startup:

The program imports the SoftwareSerial library, and establishes pins for motor control. A char named btData is used to handle incoming Bluetooth data. Then pins 2 and 3 are declared as RX and TX using SoftwareSerial.

//SoftwareSerial library is included so that we can utilize pins 2 and 3 for the HC-06
#include <SoftwareSerial.h> //Pins 4, 5, 6, 7 used for motors.
const int motorRF = 4; //RF = Right motor, Forward direction 
const int motorRR = 5; //RR = Right motor, Reverse direction 
const int motorLF = 6; //LF = Left motor, Forward direction 
const int motorLR = 7; //LR = Left motor, Reverse direction 
char btData; //char used for bluetooth data - receives commands like "1", "2", "a", etc. 

SoftwareSerial HC06(2,3); //RX, TX - Pins 2 and 3 used for HC-06 Module

 

Setup:

Serial communication is set up, and a string saying “Hello” is sent as a self-check. Then digital pins 4, 5, 6 and 7 are declared as outputs, in order to send signals to the L298n.

void setup() {
  HC06.begin(9600); //Begin serial at 9600 baud as "HC06"
  HC06.println("Hello."); //Sends "Hello." through serial, to acknowledge startup

  pinMode(motorRF, OUTPUT); //Sets pins 4 through 7 to OUTPUTs, to control the L298N
  pinMode(motorRR, OUTPUT);
  pinMode(motorLF, OUTPUT);
  pinMode(motorLR, OUTPUT);
}

 

Loop:

The loop works by cycling until data is available at the HC-06 module. When data is received, it enters the loop and then makes decisions. In this case, I use the numbers 1 through 4 to control the state of the L298N. When a ‘1’ is received, the Arduino sets pins 4 and 6 to HIGH, so that the L298N enables the outputs in a manner that turns both motors forwards. I use a delay function, so that it keeps the motor on for a second.

void loop() {
  //Loops until data is sent to HC06
  
  if (HC06.available()){ //When data is available in the HC06, do this
    
    HC06.println("Reading."); //Prints "Reading." through serial, to acknowledge incoming data
    btData = HC06.read(); //Reads "HC06" and stores the value into the char "btData"

    if (btData=='1'){ //If the HC-06 receives a 1, do this
      HC06.println("Forward."); //Sends "Forward." through serial, to acknowledge that a 1 was received
      digitalWrite(motorRF, HIGH); //Activates the motors so that the tank moves forwards
      digitalWrite(motorLF, HIGH);
      delay(1000); //Delays for approximately one second
      
    }
    if (btData=='2'){ //If the HC-06 receives a 2, do this
      HC06.println("Reverse."); //Sends "Reverse." through serial, to acknowledge that a 1 was received
      digitalWrite(motorRR, HIGH); //Activates the motors so that the tank moves backwards
      digitalWrite(motorLR, HIGH);
      delay(1000); //Delays for approximately one second

    }
    if (btData=='3'){ //If the HC-06 receives a 3, do this
      HC06.println("Left."); //Sends "Left." through serial, to acknowledge that a 1 was received
      digitalWrite(motorRF, HIGH); //Activates the motors so that the tank rotates left
      digitalWrite(motorLR, HIGH);
      delay(1000); //Delays for approximately one second
    }
    if (btData=='4'){ //If the HC-06 receives a 4, do this
      HC06.println("Right."); //Sends "Right." through serial, to acknowledge that a 1 was received
      digitalWrite(motorLF, HIGH); //Activates the motors so that the tank rotates right
      digitalWrite(motorRR, HIGH);
      delay(1000); //Delays for approximately one second

    }
    digitalWrite(motorLF, LOW); //Turns all of the motors off, by setting everything to LOW
    digitalWrite(motorLR, LOW);
    digitalWrite(motorRF, LOW);
    digitalWrite(motorRR, LOW);
  }
}

Download the full code here.

 

Connecting to the HC-06

I use the mobile app Bluetooth Electronics to connect to and send commands to my HC-06 module. I like using my phone since I can follow the car around. You can also use PuTTy, or another program to send serial commands to the HC-06 from a laptop or desktop.

The HC-06 becomes available for pairing when it is powered on. Pair your device with it, using the default password of “1234“. Once your device is paired with the HC-06, you’ll be able to connect to it using your program of choice.

To connect to it using Bluetooth Electronics, make sure that you’ve paired your device with the HC-06 and then open Bluetooth Electronics. Click “connect” at the top, and select your HC-06 from the list. Assuming you wired it correctly and it’s paired, you will now be able to send commands to it through the app. The app makes it incredibly simple to create a customized GUI for sending commands to the tank.

 

Future Design Ideas

I plan on making a lot of changes to this tank. I’m going to redesign the majority of the frame and the connection points on the wheels so that they are stronger. I want to increase the number of batteries to 3, so that it’s capable of higher speeds. The battery holder design is a little bit too short, requiring tape to stay closed, so I’ll fix that in the next revision.

 

I am working on a standalone program so that the project can be controlled in an easier manner. Instead of having it drive for predetermined lengths of time according to command-line strings, I plan on having a GUI with realtime feedback. There are a lot of options for making a program like this. I have been experimenting with python to some success, but I might resort to using one of the many application builders that are available. For right now, the Bluetooth Electronics app meets all of my requirements so I’ll continue down that path until I need more complicated functionality.

 

A great upgrade for the system would be to use an ESP8266. It would provide greater control options, and it would lower the cost and footprint. The extreme simplicity of the Arduino and HC-06 combination make it very easy to use and adapt, so I am going to continue using it for this project. Plus, I have a bunch of Nanos and HC modules sitting in a drawer collecting dust; it’s about time I turned them into something. My next RC vehicle project will hopefully utilize wifi.

 

More on this project is coming.

Thanks for reading!

 

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ProGrow Update #5 – Bluetooth using HC-06

Progrow Side - Feb 16 2017. HC-06 visible in the top right

I’ve been severely neglecting the ProGrow the past couple of weeks. The cat grass died a while ago, but I’m planning on planting some catnip in the future. Right now, I’m going to try to focus on getting some wireless functionality into it. I have an ESP8266 module that is capable of adding Wifi to the system, but I also have an HC-06 Bluetooth module. I’m going to test out the Bluetooth for now, so that I can send commands to it from my phone or PC.

The HC-06 and HC-05

HC-06 with Breakout Module Front View
HC-06 Bluetooth chip with breakout module, Front View

The HC-06 and HC-05 are inexpensive and easy to use Bluetooth modules. The 05 and 06 are virtually the same, but the HC-06 is only capable of acting as a slave, while the HC-05 is capable of acting as a master/slave. The blue board in the picture above is a breakout board with a voltage regulator for the primary chip.

Adding the HC-06

It’s incredibly easy to wire up the HC-06. All I had to do to connect it to my Arduino UNO was:

  • VCC to 5V
  • GND to GND
  • TX to Pin 2
  • RX to Pin 3

If your module has a breakout board attached, then it will be 5V tolerant. If it is a bare module, you’ll need to make a voltage divider in order to provide 3.3V to the chip.

 

HC-06 with Breakout to Arduino UNO Schematic
HC-06 with Breakout to Arduino UNO Schematic

Connecting with the HC-06

I’m using the library SoftwareSerial to utilize my digital pins 2 and 3 as RX/TX,  instead of 0 and 1. This is because when you have something connected to pins 0 and 1, and try to upload to the board via USB, it can cause a communication issue. At least it did that for me.

All I had to do was include the SoftwareSerial library, and then initialize pins 2 and 3 using:

SoftwareSerial HC06(2,3); //RX, TX

That way I can use “HC06” for serial functions on different pins. It has to go before the setup function.

 

I’m using a Bluetooth dongle on my PC to send commands to the HC-06. I can connect to it with the Windows Bluetooth interface, using the default password of 1234. I’m using PuTTY to connect to the COM port that is associated with sending data to the HC-06, and then I send commands through the PuTTY terminal.

I can read data that is sent to the HC-06 using:

btData = HC06.read();

Then I can use a simple if statement to make decisions based on whatever value I sent to the module. For example:

if (btData=='1'){
    displayData(); //displays all sensor values on screen
}

 

What’s Bluetooth needed for?

Right now I use the Bluetooth to issue basic commands wirelessly. I can send commands to the ProGrow from my computer using Putty. I can have the system output to the display, water the plant, write to the SD card, change the automatic sample delay and force a measurement.

 

What’s next?

I want to use an HC-05 module instead, which will give me many more connectivity options.

I am going to design new cases for all of the modules. My goal is to create a single box that will house all of the primary components, instead of having them distributed across the front or side of the container. I also want to get some catnip planted.