There was a chassis with motors, and I thought they will be just fine. It looked good on preliminary tests, when they where controlled in a "classic" way, like an RC car. But that speed was too fast. Driving motors with ~30% PWM gave an acceptable speed, but poor power. It sometimes struggled on a carpet going straight ahead. Having 40% PWM made it reliable, but too fast. So I searched around, and found a popular, highly geared stepper motor: 28BYJ-48. It's unipolar, and comes with the ULN2003 driver. Uses 4 pins per motor, and that means too much pins for ESP8266 :) I have an idea of using an MCP23017 to expand the ESP with 16 additional pins. I bought a two 18650 cell power bank also, and I hope, its electronics could supply enough current to power both motors and the ESP. I am expecting it to arrive soon.