To construct a robot we need following parts−

a. Power Supply
Generally, robots are powered by batteries, solar power, hydraulic.
b. Actuators
Basically, we use this to convert energy into movement.
c. Electric motors (AC/DC)
Generally, we need this for the rotational movement.
d. Pneumatic Air Muscles
Basically, we can say that they contract almost 40% when the air is sucked in them.

e. Muscle Wires
Although, we have noticed that it contract by 5% when an electric current is passed through them.
f. Piezo Motors and Ultrasonic Motors
Basically, we use it for industrial robots.

g. Sensors
Generally, we use it in task environment as it provides information of real-time knowledge.