#Design Inspiration#

One day, Wangzai’s grandmother took the child out to play and encountered a little friend riding a small car. Wangzai particularly wanted to ride his friend’s car, so the other grandmother let him ride it. However, once Wangzai got on, he was very reluctant to get off. We also have a car like that at home, which is pushed by hand. Wangzai’s father then had an idea to modify the car so that the children would enjoy playing with it, and the grandmother wouldn’t have to push it. Thus, today’s project was born.

First, let’s take a look at the demonstration video.

#Solution Confirmation#

The main purpose of this project is to turn the small car into an electric one, which can be controlled remotely, even using a mobile phone to control it. An electric motor will drive the car to move forward and backward, while a servo will control the left and right steering.

To add electric functionality to the small car, we must include an actuator motor, and the selection of the motor is crucial. Moreover, since it needs to carry a child, we cannot use a very ordinary motor. Therefore, we purchased a 735 motor from a children’s pedal car on a shopping platform.

Once the motor was determined, the next question was how to choose the motor driver. The 735 motor is a brushed DC motor. The simplest and most direct method is to use a brushed DC motor controller to drive the motor. The data is sent from the car model or aviation model’s remote control to the receiver to control the car’s movement. We can also add a servo to control the steering. This solution is evidently feasible, as there are many mature cases to reference, especially in the field of combat robots, where this type of gameplay is very common. Wangzai’s father had participated in a 2kg class combat robot competition before, so the electrical part can be used directly.

Besides this, are there any other solutions? Certainly, if the first solution is considered a non-programmable version, we can also create a programmable version. There are two approaches: using an Arduino Uno controller combined with a 2.4G remote control handle to control the car’s movement or steering, and the second approach is to use an ESP32 type of networked main control to achieve wireless communication for controlling the car via mobile phone Wi-Fi or Bluetooth. This sounds like a sophisticated method, and without hesitation, Wangzai’s father decided to use the ESP32 as the main control for the programmable version. Next, this article will introduce the project “Baby Stroller Toy” through two modification solutions.

#Disassembly#

No matter which solution, the first step is to disassemble the small car.

The programmable and non-programmable versions share the same driving motor and steering servo parts, so let’s start with the motor modification installation.

How to install and secure the motor while being able to drive the wheels is a critical point.

As can be seen from the following diagram, Wangzai’s father’s solution is as follows.

Using a 3D-printed shaft sleeve to fix the flange and the wheel, the 16-tooth synchronous wheel is mounted on the 735 motor shaft, and the synchronous belt drives the 80-tooth synchronous wheel on the light shaft to achieve deceleration motion.

The 3D modeling software designed shaft sleeve is shown in the following image.

After the design is completed, slicing and printing are performed.

The following shows the effect after printing is completed.

Next, the shaft sleeve is installed on the wheel, a 3mm round hole is drilled with an electric drill, and secured with screws.

Then the flange and diamond-mounted bearing are installed.

Using 3mm self-tapping screws to fix the flange with the 3D printed coupling, the bearing is secured to the chassis with 4mm screws and nuts.

The next step is to install the motor and the transmission components. The following image shows the 2GT5mm synchronous belt and 16-tooth and 80-tooth synchronous wheels.

The 735 motor is fixed to the chassis using the angle bracket shown in the following image.

The final appearance of the actuator motor and driving wheel after modification is shown in the following image.

After the driving motor is modified, the next step is to introduce the steering servo. This project uses a 270-degree metal digital servo produced by DFRobot, with a working voltage of 4.8~7.2V and a load of 15Kg, which is sufficient for the steering servo of the small car.

With the servo, we also need 1 servo arm and 1 ball head pull rod to control the car’s steering.

The installation effect of the servo is shown below.

The installation of the servo arm and ball head pull rod for the steering part is shown below.

After modifying the common motor part and servo part for both versions, we will learn how each version achieves other functions.

#Non-Programmable Version#

Below is the hardware list used in the non-programmable version.

·735 DC motor *1

·15kg/270-degree metal servo *1

·Brushed motor controller *1

·Fus remote control *1

·Fus receiver *1

·3s 1800mAh lithium battery *1

·Servo adapter board *1

·Boat switch *1

·Hardware parts, wires, and power connectors as needed

The Fus FS-i6 2.4G 10-channel remote control.

The circuit wiring is shown in the following image. The power supply uses a 1800mAh 3s lithium battery. The brushed motor controller is connected to the receiver’s channel 2, and the servo is connected to the receiver’s channel 4. A dedicated expansion board is used to power the servo.

The effect after wiring is shown in the following image (the servo image was missed).

To facilitate use, a hole was made in the car’s outer shell to install the switch.

Finally, let’s test how the non-programmable version performs.

#Programmable Version#

Next, let’s understand how the programmable version achieves its functions.

First, let’s get to know the electronic hardware used.

The main control we chose is the ESP32, utilizing its Wi-Fi or Bluetooth wireless communication functionality, allowing us to control the car anytime, anywhere, which significantly enhances the quality of our project.

The next key component is the driving motor driver, which must be capable of carrying the weight of a child. The working current of the motor driver must be sufficiently large; thus, we selected the following DC motor driver, which operates at a voltage of 12~36V and a working current of 12A (without cooling) to 20A (with cooling).

The DC motor driver board has three control pins: two pins control the direction, and one pin controls the speed. It also has a 5V power output. The following two images show the function introduction of the pins and specific usage methods.

Finally, Wangzai’s father added music and lighting functions to the car. For the music function, the DFPlayer Mini MP3 module was used (a micro SD card is needed). This module is compact and powerful, directly controlled via serial communication, and can drive an 8Ω/0.5w speaker directly.

The following image shows the specific usage method of the MP3 module pins.

The lighting function uses ws2812 LED strips.

The complete electronic list is shown in the following image, using a high-power adapter board to power the servo, and the main control ESP32 uses an expansion board to facilitate wiring. The actuator motor is still the 735 motor.

The wiring diagram for the programmable version is shown below.

To facilitate the installation of electronic components, a plane-shaped bottom plate was designed, which also serves as a footrest for children. The design drawing is shown in the following image.

The following image shows the physical object processed by a laser cutter from a 3mm linden wood board.

After completing the wiring, the effect is shown in the following image.

Drilling holes and wiring to install the ws2812 LED strip to add lighting functions to the car.

Like the non-programmable version, the power supply also uses a 1800mAh 3s lithium battery, and a battery case is specially designed to connect to the plane bottom plate.

The final effect display after assembly is shown in the following image.

#Program Design#

The program design mainly involves two parts: the Blynk mobile terminal remote control component settings and the program writing for the ESP32 main control. Let’s first set up the Blynk mobile terminal.

Blynk Setup

The first step is to log in. If it’s your first time using it, you need to register first. As shown in the following image, “Login” is for logging in, and “Create New Account” is for registration.

Enter your username and password to log in.

After logging in successfully, click the plus sign on “New Project” to create a new project.

Next, select the main control as ESP32 Dev Board.

Click “CONNECTION TYPE” to choose a connection method.

For this task, we can choose between Wi-Fi and Bluetooth. In terms of control response speed, the Bluetooth mode is slightly faster and has almost no delay. Wangzai’s father will explain using Bluetooth mode, so we choose the “BLE” mode here.

After the selection is complete, click the “Create Project” button. It will ask whether to send an email containing the authorization code to your email. Click OK to create the project and receive the email. Of course, you can also find the authorization code in the project. This authorization code is the key for the Blynk mobile terminal to connect with the ESP32 control board via Bluetooth.

Clicking the hexagon in the upper right corner will take you to the project settings interface, where you can also see the authorization code information at the bottom.

Swiping left on the app allows you to add components. The component list is shown in the following image. For this task, we need to use 1 button, 2 styled buttons, 2 joysticks, and 1 Bluetooth component.

The loaded components are shown below.

We place it horizontally for easier explanation, which is also the posture during control. Since Blynk does not yet have a horizontal screen feature, some words may look a bit awkward, but this does not affect our usage.

Why use two joysticks? It is for convenience. We use the left joystick to control forward and backward movement and the right joystick to control steering. The left joystick is set to virtual pins v0 and v1, while the right joystick is set to virtual pins v2 and v3. The setting process is shown in the following image.

V2 pin controls the rotation angle of the servo, which in turn controls the car’s steering.

After testing, the value range setting for the virtual pin controlling the steering (V2) is set between 60 and 120 to allow the car to turn left and right flexibly, while the virtual pin for controlling speed (V0) is set between 0 and 160 to provide enough power to carry a child.

Next, we need to set up two types of buttons: “Button” and “Styled Button”. Why two types? The principle is the same; both can achieve the desired function. However, for aesthetic reasons, Wangzai’s father chose different buttons.

The three buttons are virtual pins V4, V5, and V6. The left one is V5, the right one is V4, and the middle one between the two joysticks is V6. Observant readers might notice that some button settings have different modes. Indeed, button settings can be selected as either “PUSH” or “SWITCH” modes.

V4 virtual pin is used to honk the horn, set to “PUSH” mode, which plays a honking sound and flashes the light strip effect when pressed, and resets when not pressed.

V5 virtual pin is used to control whether to play music, set to “SWITCH” mode, pressing once starts playback and pressing again stops it.

V6 virtual pin is used to control the lighting, set to “SWITCH” mode, pressing once locks the lighting mode, pressing again stops the lighting.

The last component that needs to be set up is the Bluetooth module. Click on the Bluetooth module to see the interface shown below, then click “Connect BLE Device”.

Select the Bluetooth name found during the search. This name is set in the program, so find the name you set and click “OK” to wait for the connection to succeed.

Finally, click the triangle in the upper right corner to run this program.

After setting up the components of the Blynk mobile terminal, we will write the program for the ESP32 main control.

The programming environment options for this project include Mind+, Mixly, and Arduino.

Since the Mind+ programming environment does not support Blynk for the ESP32 board, and Arduino IDE is quite obscure for most people, Wangzai’s father chose the Mixly programming environment for this project.

Mixly Program Design

First, let’s understand the programming method for Blynk. Open the Mixly programming software, select Arduino ESP32 in the lower right corner, and choose the “Blynk IoT” module from the “Network” section in the left module bar, dragging the “Blynk BLE connection” module to the right programming area. Then modify the “Blynk authorization code” and “BLE name”. The authorization code here is like a key and needs to match the one in the Blynk mobile terminal.

After setting up Blynk, we can try to perform some small tasks.

For example, we can choose “Get Data from App…” from the “Blynk IoT” section in the left “Network” module. This module is the most frequently used in this project. Once we master this simple application, we will understand most of the others.

We can try writing a program like the one below. When the V4 virtual pin receives data, it will execute three actions: first, print the received data in the serial monitor for debugging purposes; second, play the fourth song on the MP3 module; and finally, execute a custom function called “Blinking Eyes 2”. If you don’t get too caught up in the MP3 module and custom functions, the program is actually quite easy to understand.

MP3 and LED Strip Program

So how does the MP3 module play songs? What preparations are needed? Obviously, some are needed.

We need to select the program block to initialize the MP3 from the “Actuators” section in the left module bar. Here, Wangzai’s father would like to thank Teacher Qiu Jiongtao, as the latest version of Mixly does not yet support the Mini MP3 module for the ESP32. Teacher Qiu specially helped create a graphical library, allowing Wangzai’s father to use the MP3 module. Teacher Qiu also provided significant help in debugging the Blynk mobile terminal program, and we are very grateful for his support and contribution to the Blynk ecosystem. Teacher Qiu is also a father, and this little car can be played by his baby too.

The specific initialization program is shown in the following image. The MP3 module communicates with the ESP32 using a software serial communication method. Note that when wiring, the MP3 module and ESP32 must be crossed, that is, RX-TX, TX-RX.

Careful readers may wonder how the songs are numbered and how to set them up. This is a very good question. The MP3 module, known as the DFPlayer Mini MP3 module, can take a micro SD card. The songs we want to play are stored on this SD card, and the MP3 module can read most audio file formats. However, the song files must be named with numeric codes like “0001” and placed in a folder named “mp3” on the SD card. After these preparations, you can enjoy your music. The fourth song in the program is the honking sound, and the fifth song initialized in the program is the sound of the car starting. Additionally, it is best not to place the MP3 playback program in a loop, as this requires adding wait times to hear the song. Instead, it can be placed in a function and executed when conditions are met.

Next, let’s explore the custom function “Blinking Eyes 2”. Blinking Eyes refers to controlling the WS2812 LED strip. The program is shown in the following image.

Even if you don’t understand the above program, that’s okay. Let’s look at a simpler example. The following program allows a string of 16 LED beads to all light up red.

The control program for the LED strip can be found in the “Actuators” section of the left module.

Of course, the initialization program is also necessary, as shown in the following image.

If we change the color to black, the effect will be to turn off all the LED beads.

In addition to using built-in colors, we can also adjust the color using RGB values, theoretically allowing for 256*256*256 different colors. The program can also include a delay display time for the LED strip to create a flowing effect.

After understanding the simple example, we can easily comprehend the custom function “Blinking Eyes 2”. From previous discussions, we know that when the V4 virtual pin receives data, i.e., when the Blynk mobile terminal’s V4 button is pressed, it will produce a honking sound while the LED strip shows the blinking effect. The custom function “Blinking Eyes 2” makes the LED strip light up white and gradually adjust the brightness from 1 to 100, then dim from 100 to 1, and finally turn off. This process of gradually brightening and dimming is repeated three times.

After mastering the custom function “Blinking Eyes 2”, we also have another custom function called “Blinking Eyes”, which operates on the same principle, but the LED strip lights up red. Let’s take a look at the program for “Blinking Eyes”.

After understanding the “Blinking Eyes” custom function, the other LED strip programs become much simpler. For example, the following program detects when the virtual pin V6 is “1” (ON), it lights up the white LED, simulating the car’s headlights at night. Conversely, when it is “0” (OFF), the light turns off.

Through the above introduction to the WS2812 LED strip and MP3 module, I believe everyone will have many ideas for the diverse display effects of the LED strip and MP3 playback. I look forward to everyone implementing their ideas.

The explanation of the LED strip and MP3 program comes to an end. Next, let’s learn about the steering program for the servo.

Servo Steering Program

Using the V2 virtual pin to control the steering of the servo, we need to find the program block to control the servo in the left module bar.

Next, we can try writing a program like the one below. When the V2 virtual pin receives data from the mobile terminal, it will do two things: first, print the received data in the serial monitor, and second, make the servo rotate to the corresponding angle based on the received data.

To ensure the car can turn correctly, after testing, the angle range for the servo is set between 60 and 120 degrees, with the default state at 90 degrees (straight). Angles between 91 and 120 degrees indicate a left turn, while the LED strip executes the left turn program. Angles between 60 and 89 degrees indicate a right turn, while the LED strip executes the right turn program. It is important to note that the servo is installed on the chassis of the car, and during testing, the car should be turned upside down. When setting the angles for left or right turns, make sure to adjust the car with the front facing up to prevent incorrect adjustments. The improved program is shown in the following image.

The above program involves two custom functions: “Left Turn” and “Right Turn”. Below, we will introduce these two custom functions. Similar to the previous LED strip display program, we divide the 16 LED beads into two groups: the left group with 8 beads and the right group with 8 beads, based on the driver’s perspective sitting in the small car.

When the car needs to turn left, the left 8 beads will flash to indicate the turn. The LED strip’s turning effect references the design of Audi’s turn signal, presenting a flowing effect from the inside out.

The following is the “Right Turn” custom function, which is similar to the “Left Turn” function, except for the different LED bead numbers.

Forward and Backward Program

After mastering the steering program, let’s learn how to make the car move forward and backward. The forward and backward movement of the car is controlled by the V0 virtual pin. The program has three cases: forward “forward”, backward “backward”, and stop “stop”. The value range for the V0 virtual pin is 0-100. When the value is equal to 0, the car stops, executing the “stop” custom function. When the value is greater than 51, it executes the forward “forward” custom function, and when the value is less than 49, it executes the backward “backward” custom function.

Backward

Forward

Stop

Through the following animated images, we can see the testing effects of the above program.

The final program for music playback uses the state of the V5 virtual pin to control whether to play music. When the value of the V5 virtual pin is “1” (ON), it starts playing music randomly and executes the custom function “Inward Flow”. When the value of the V5 virtual pin is “0” (OFF), it stops playing music.

Some partners may ask if there is an “Inward Flow”, is there an “Outward Flow”? Indeed, there is. The effect of the “Outward Flow” is presented in red when the car starts.

Finally, let’s look at the complete program. Since the program is lengthy, parts of it that have already been introduced will be folded.

#Summary#

This “Baby Stroller Toy” project has not been tested for battery life, and reference data will be provided after testing. During the modification process, we encountered a situation where the steering servo and driving motor could not work simultaneously. After help from Teacher Qiu, we discovered that it was due to incorrect pin selection on the ESP32. This experience taught Wangzai’s father the importance of comprehensively mastering the various parameters of the main control board.

Additionally, this design and production stemmed from an experience in life. The process of modifying the project allowed Wangzai’s father to learn a lot of knowledge and skills. This project involved many areas of knowledge that were previously unfamiliar. To complete the project, one must explore and learn with questions, mastering it rather than passively accepting textbook knowledge. Learning new knowledge with the goal of achieving project functionality will solidify the knowledge system and enhance the level more quickly. In summary, there is knowledge everywhere in life; careful observation, in-depth thinking, attempting changes, and maintaining a lifelong learning attitude are essential. Learning from life and contributing back to life is the goal.

We welcome more like-minded parents to communicate and improve together, and we also welcome criticism and suggestions for this article.

Creating makes life better, and we look forward to meeting you again next time.