Chassis

Read: Vex's Guide on Chassis Design

As VEX said, the main things to consider are purpose, size, shape, and shaft support.

Purpose

The purpose for a chassis is usually to allow movement of the robot as a whole. But there could also be alternative purposes such as to align to walls or to latch onto game objects.

Size

Most chassis take advantage of the 18 in x 18 in x 18 in starting size limit. This means using the longest metal bars (35 holes) to maximize the size. A large robot makes it possible to add many mechanisms onto it and is future-proof. The weight should also be considered as if it is too light, the robot can tip and fall easily, deeming the robot unusable. But if it was too heavy, it will be slow and hard to move. So aluminium bars are recommended although steel could work as well.

Shape

There are 4 main shapes for a chassis, which will all be introduced.

H Drive (Top Left)

The H Drive is quite convenient as it allows for the robot to move in all 4 directions. But it requires quite a lot of space and at least 3 motors but preferable 5.

Tank Drive

The tank drive is the most common chassis shape. It moves forwards and backwards but moves sideways by pivoting. It could cause inconvenience but due to its simplicity, it could be a good option, especially for beginners.

Square Base

The square base is quite uncommon as it requires 4 motors and moves in a diagonal direction. Although it is omnidirectional, it is quite hard to place mechanisms on top due to its diagonal nature.

X Drive

The X Drive is omnidirectional and is quite convenient as it does not move diagonally. It has a problem of having the possibility of being structurally unsound as the curves around the wheels are hard to connect to other bars.

Shaft Support

This is the most important factor in chassis design as if the shafts are unstable, the chassis will drive inaccurately, failing your autonomous. For the best shaft support, there has to be at least 2 points of support. This means having the axle connected to at least two structurally sound bars. A structure as shown in the photo to the left is recommended as the wheel is between two bars, although the axle needs spacers to fill the axle.

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