I will build a small two rooter from sketch. For a prototyping phase I will reuse some of my former projects. Later all electric components will be on a single PCB. The motors will be also directly mounted under this PCB.

Control

• ESP8266
  • Handel wifi communication
  • AP if no local wifi network available
  • host website for controlling and/or sensor data
  • Communicate to Atmega via UART.
  • if enough time: Use ESP8266 as WIfi UARTbridge to flash the ATmega
• ATmega (probably ATmega 328p like on Arduino Nano/Uno)
  • Cotnrolls all motors and sensors.
  • Gets commnds from ESP8266 via UART
  • Sends sensor data back via UART
  • Easy to reprogram (all default functions packed into library)
• UART-USB bridge
  • first version will definitely have an CH340 or similar on board. To program both controllers from USB. And for debugging.
  • In later versions this will be deleted or not populated with parts.

Power

• single cell Li-Po or LI-Ion battery.
• Battery charging circuit on board (perhaps similar to circuit I used here: #ESP8266 (ESP-07/12) Dev Board )
• Micro USB connector for charging (like modern phones)
• 3.3V regulator for ESP module and sensors.
• Motors will be run direct from the cell voltage or if higher voltage needed via step up converter.

Sensors:

• Air pressure: I did work with Bosch's BMP180 before. So I will use this or a successor.
• Humidity: Maybe SHT21 from Sensirion.
• Temperature: Normally included in Air pressure and Humidity.
  
• Anti Collision:
  • Tact switches for emergency stop
  • Ultrasonic: If there is enough time I will built a custom single transducer i2c module.
• Infraed line follower: Basic setup with on LED and two optotransisitors.

Motors / Wheels

• cheap DC gear motors or miniature stepper motors. Some further experimenting is needed here
• If DC Motors I will reuse #DRV8836 Breakout (for prototyping, later only the same IC)
• small LEGO wheels (I did found a nice overview here)

Additional thinks ideas

If there is enough time (or if I like it) I am thinking of some further ides to realize. This is a ongoing lists of ideas:

• Camera support (maybe the gameboy camera) an hosting live image on webpage
• Object recognition via camera. Maybe second camera for distance measuring.
• Sound (Alarm tone or music playback)
• Servo Arm
• Some mechanism to climb or jump up steps.
• on board display (OLED, LCD, seven segment LED or LED Matrix)