SMARS uses small 6v 150RPM motors to drive the robot around. These cannot be powered by the Arduino or Raspberry Pi directly and so need a driver board.
The Quad SMARS uses 8x SG90 servos.
These are cheap and easy to use. Because we use 8 of them we use a servo driver to both provide extra power, and also to reduce the number of data pins required on the Arduino, Raspberry Pi or Microbit.
The Quad SMARS uses a PCA9685 servo driver board to power and control the 8x servos (legs and feet). Some version of this board come pre-assembled; the servo driver cover doesn't have a hole for the large capacitor, but you can safely de-solder this (or just cut the legs off). You may also need to bend the header pins to the upright position to fit in the servo driver cover.
A bluetooth module can be easily added to a SMARS robot, there is code available for Arduinos and Raspberry Pi's so that you can remotely control it.
The HC-06 bluetooth modules are cheap and connect to a TX and RX pin on the Arduino/Raspberry Pi/Microbit.
The Raspberry Pi Zero WH is an excellent choice for driving a SMARS, they are cheap, have loads of GPIOs and the 'W' model comes with built in Wifi connectivity.
The Raspberry Pi Zeo 'WH' comes with pre-soldered headers to make connecting to power and driver boards even easier.
The Micro:bit is a small 32bit single board computer. These are very popular in the UK; in 2016 each pupil in year 7 in high school was given one
An Arduino Uno is an excellent option to drive your SMARS. The SMARS case was specifically designed for the Arduino UNO (or clone).
Official Arduinos are more expensive than Raspberry Pi Zero WH's and are only 8 bit but there is a wide range of open source code available, and they have plenty of IO pins.
SMARS can be powered by a 9v battery or via 2x rechargable 18650s. Arduino's, Raspberry Pis and Microbits are strictly 5v (or 3.3v) only, so make sure you don't connect the 9v battery directly to them.
SMARS needs a motor driver board (also called a sheild) to provide additional power, and controller chips in a single convenient package. Motor driver boards are widely available.
The ultrasonic sensor is non-contact distance measurement module, detecting objects from 2cm to 5m. There are a couple of different types of module, the one pictured here is the HC-SR04, which uses 4 pins: GND & VCC, Trigger and Echo.