Converting RC toy to bluetooth control

As a hobby electronics project, I converted the RC Mighty Excavator toy of my son to bluetooth control. I got rid of the original controller and we can now control the four DC motors of the toy from any Android phone or tablet.

This project had the following benefits:

1. Learning how to control DC motors with motor drivers and PWM.
2. Basic understanding of how to use a bluetooth module (HC-06)
3. Soldering on a perfboard.
4. Designing a basic PCB, getting it manufactored in China. The fact that EasyEDA works in the browser without the need to install anything, it's integration to JLCPCB and the low price and high quality of PCB production is fantastic.

Parts list:

1. HC-06 Bluetooth module
2. Arduino Pro Micro
3. L293D driver (2x)
4. PCB or perfboard
5. 9V battery (2x)
6. Arduino Bluetooth Controller app installed on Tablet.

Arduino source code is on gist.

End result:

Photos of the process:

Prototyping with Arduino Uno:

Perfboard top (Arduino Pro Micro and two L293 drivers):

Perfboard bottom (a soldering nightmare):

PCB that replaced perfboard:

Components placed on PCB:

Bluetooth module vertically squeezed between L293D and Arduino Pro Micro and soldered to Pro Micro:

PCB and batteries mounted to bottom of toy: