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# Drive Trains
Drive trains are not technically required, but nearly every robot has one. They allow the robot to traverse the field, and serve as a foundation for the rest of the the robot.
Here's the simplest possible drivetrain you can have:
Simple tank drivetrain CAD
This tank drivetrain features at least 2 omniwheels on each side of the robot. Usually, 4 or 6 motors will power these omniwheels either directly or through gears. This drivetrain can turn in place and go forwards and backwards, but it cannot strafe side-to-side (which is usually not necessary).
Here's another example of a more complex tank drive with 6 motors, 6 wheels, and a gear system:
Example drivetrain CAD
Another type of drivetrain is the X-drive. This drive has more maneuverability, but reduced torque and pushing power relative to the standard tank drive.
Photo credit: Team 1619Z
While the increased maneuverability does offer an advantage in niche scenarios, X-drives are very weak against defense by others teams. For example, out of the 20 teams that won their division during Spin Up Worlds (i.e. top 20 teams in the world), all 20 of them used a tank drive.
There are another couple types of drivetrains, but these are not competitively viable in VEX Robotics.
Overall, the recommended drivetrain for both new and experienced teams is the standard tank drive.
## Design Guidelines
Let's assume you're going with the tank drivetrain (please do!). Here's a few general guidelines to keep in mind while designing it.
* Smaller is generally better, but don't make a drive so small that it can't fit other mechanisms on the top of the robot
* Don't use any more gears than is absolutely necessary, to reduce friction
* Have the wheels as far apart as possible, which makes it harder for the robot to tip over
* Use 2-3 cross-braces, and have them as far apart as possible. This keeps the chassis from bending under heavy defense
Here's another example CAD that follows these guidelines. Always CAD the drivetrain before building it!
Over Under drivetrain CAD from 96504C
## Additional Resources
Here's two videos on how to square the chassis--this is very important for having consistent autonomous and a low friction drivetrain.
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