In robocraft there are multiple different movement types which you can use for your robot. What movement type you use decides how you will build your robot. Here are the movement types. If you had 25 mega versions of the movement parts as of 11/14/18 you will have gotten a golden version of the part. There is also a carbon 6 version of the sprinter legs.
Tank Treads:
Tank treads are high health , you guessed it tank treads. Most tanks have 3+ tank treads although you can still turn and function with 2.
Hover Blades:
Hover blades are small spinning blades that are used to make your bot hover. Most hovers include lots and lots of them as they have somewhat low health each and are easily unbalanced by bad weight distribution.
Aerowings/Rudders:
Aerowings/rudders are used in planes and other flying robots. A basic plane requires 2 wings, 3 rudders and thrusters to function although it is better to have more so they are harder to kill. Although it is possible to control a plane that only has 3 rudders it is very hard.
Skis:
Ski robots use skis to steer and to keep the robot stable, these bots require thruster to move though. Ski robots require 3+ skis.
Copter Blades:
Copter blades are large rotor blades that can be put on your robot to fly. Most copters have 2+ rotor as you can't turn without thrusters if you only have 1 rotor. Rotor blades can lift pretty hefty amounts of weight so copters can be pretty tanky.
Insect Legs:
Insect legs are walker legs that stick out sideways (or backwards or forwards depending on where you place them). They are very stable so they provide a good platform for people using rails. They can also climb nearly vertical surfaces so you can get to good vantage points with them. Most walkers have 4+ legs.
Mech Legs:
Mech legs are legs that go straight down from where they are placed. Mech legs have a pretty decent amount of health with shielding on top of that making them the highest total health movement item. Most mechs use 2 legs but you can use 1+.
Sprinter Legs:
Sprinter legs also go straight down from where they are placed. Sprinter legs have the highest health but have no shielding so they have less total health than mech legs. Sprinter legs as their name implies are faster than mech legs. They can also jump far higher and after they reach top speed have a special jump which propells your robot really fast forwards but once they land, they force you to stop for a moment before you can move again. There is a way around this though, if you are turning as you are landing you won't be forced to stop. Most sprinter mechs use 2 legs but you can use 1+.
Thrusters:
Thrusters are usually used to make other movement types faster but it is possible to make robots with only thrusters. The minimum amount of thrusters you would need to make a working thruster robot is 3.
Hybrids:
Some robots will have multiple movement types either for redundancy (in case they lose one movement type) or to assist in the movement of the robot. Ex: putting a hover on a mech will make it walk slightly faster and jump a good bit faster, at the consequence of lowering the mech's jump height. Some popular hybrids are hover copters, tank mechs, walker flyers, and hover skis. Some special types of robots are drones which use rudders to provide lift but not to actually pitch the robot, all the movement is provided by thrusters inside the robot.