This instructables show how to use a metal sweet box make a robust remote toy car. Since It made from metal case and all parts hide in there, it is not easy to break even kids step on it.

Step 1: Preparation

Metal Sweet Box

Any metal sweet box that can fit in all component is ok, square box is better but not essential. P.S. the sweet in the box I bought (55 x 55 x 20 mm) is not taste good enough for me to recommend it :P

Small Motor

The motor I bought is actually come from the parts of Eyelash curler. It have a specialty cross shape axle, I accidentally found it have same form factor as Lego wheel! What a coincident!

It help me make a very small toy car, but it is now out of stock after I bought 10 :P

https://world.taobao.com/item/530495450790.htm?fro...

Wheel

Lego part no. 59895 x2 and 4624 x2

8mm Steel Ball Omni Wheel

2 ball wheel for helping the toy car run smooth

ESP8266 Board

ESP-07 or ESP-12E is recommended.

DC/Stepper Motor drive Board

Any motor drive board that can support drive 2 bidirectional motors should be ok. I just have a TB6612FNG board in hand.

Lipo Battery

As large as possible that can fit in the box remaining space is recommended, depends what you have in hand

Soft EPE packing foam

I am making a robust toy car, so I need some shock absorption material. You can easy found it from the product packing.

Other Parts

A small switch for switching power; 2 pins female connector for connect external Lipo charger; some coated copper wire(color is not essential); a Lipo charger; a USB serial cable for initial program the ESP board.

Step 2: Modify the Metal Sweet Box

All parts hide in the metal box, only the wheels expose a little bit at the bottom.

measure your box, wheel and ball wheel
remove the box cover and other parts for ease of drilling
mark the wheel hole at the box bottom, 2 wheels and 2 ball wheels in diagonal
drill the hole at small size drill first, say 2mm (drill thin metal plate by large size drill not easy to handle)
enlarge the hole by a reamer
use metal cutter cut out the wheel shape
use a flat plier fold and hide the metal sharp part

Step 3: Toy Car Suspension System

Metal case is strong, but motor, gear and wheel are weak. I use soft EPE packing foam to hold the wheels for absorb the shock.

cut the foam fit into the metal case
cut the ball wheel hole in diagonal
test it can fit on the metal case
install the Lego wheel to the motor
cut out the space for the wheel and motor
cut out the space for the battery
test it can fit on the metal case again

Step 4: Flash the ESP Board

Follow my previous instructables to connect and flash NodeMCU firmware and upload nodemcu-httpserver.

Step 5: Soldering Work

Power Unit

The toy car cannot fit the charge board, so only line out the charger pin header to connect external charger board

Lipo +ve -> charger pin header -> power switch -> Vcc
Lipo -ve -> charger pin header -> GND

cut the foam to install the pin header and switch

connect external charge board to charger pin header for test charging

Motor Drive Board

Vm  pin -> Vcc
Vcc pin -> Vcc
GND pin -> GND
A01 pin -> right motor
A02 pin -> right motor
B02 pin -> left motor
B02 pin -> left motor

ESP Board

EN pin     -> Vcc
GPIO14 pin -> motor drive PWMA pin
GPIO12 pin -> motor drive AIN2 pin
GPIO13 pin -> motor drive AIN1 pin
Vcc pin    -> Vcc
GPIO5 pin  -> motor drive PWMB pin
GPIO4 pin  -> motor drive BIN2 pin
GPIO2 pin  -> motor drive BIN1 pin
GPIO15 pin -> GND
GND pin    -> GND