Drivetrains

Drivetrains

A Drivetrain is the mobile base of a robot. It includes the wheels, motors, gears, and structure that lets the robot move around the field. Choosing the correct drivetrain is important and can determine how fast, how agile, and how powerful your robot will be. There are many types of Vex Drivetrains that vary in complexity. The 4 most common are:

• Tank Drive
• Mecanum Drive
• X-Drive
• H-Drive

Tank Drive

A traditional Tank Drive uses standard wheels where the wheels on the left are controlled by an independent motor from the wheels on the right.

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• How it moves: To go straight, both sides must spin forward. To turn, one side spins forward while the other side spins backward.
• Pros: Tank drive gives good traction on the ground which makes a robot hard to push around and great at climbing over obstacles.
• Cons: Tank drive robots cannot move directly sideways, giving it limited mobility.

Mecanum Drive

Mecanum Drive uses 4 special Mecanum wheels which have a special rollers at a 45 degree angle around the rim. The wheels must be mounted in a specific configuration for Mecanum drive to work correctly.

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• How it moves: By spinning the 4 wheels in different combinations, they can apply different forces, allowing the robot to drive in any direction. For example, if you spin the front-left and back-right wheels backwards, and the front-right and back-left wheel forwards, the robot will move staight left without needing to turn.
• Pros: Mecanum drive can move smoothly in any direction which is great for lining up with a goal quickly.
• Cons: Mecanum drive can be complicated to code and because the wheels force is applied at a 45 degree angle, its overall pushing power is lower than a standard tank drive.

X-Drive

An X-Drive robot uses omni wheels at the 4 corners of the robot, but each wheel is rotated at a 45 degree angle pointing outwards like the letter “X”.

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• How it moves: Like mecanum drive, it can move in any direction by combining different wheel rotations at the same time.
• Pros: X-Drive is very fast, about 1.41 times faster in straight lines than a tank drive using the same motors. X-Drive is also highly agile and can turn quickly.
• Cons: X-Drive is very complex and requires a perfectly square robot. It also has relatively low pushing power.

H-Drive

H-Drive looks similar to an Omni-Directional Tank Driev, but with one or two extra omni wheels mounted sideways directly in the center of the robot, hence the name H-Drive.

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• How it moves: The ouder wheels handle forward, backward, and turning, while the center wheels are linked to a seperate motor and handles sideways motion.
• Pros: Simple to code and build compared to X-drive and Mecanum Drive. It gives you the full pushing power of tank drive when moving forward, but still lets you slide sideways when needed.
• Cons: If the field is uneven, the center wheels may lose contact and slip on the ground. It also requires an extra motor dedicated entirely to the center wheels.

Different drivetrains require different code and different controls to work intuitively.