Robotics/Physical Construction/The Platform

Most robots need a framework of some sort to which the builder attaches the various components and subsystems that make the robot function. This framework is known as the platform.

A good platform has a few requirements:
 * It has to be light. Don't use steel unless you really need the extra strength. Plexiglass (or any other hard plastic) with an aluminum framework for strength can be sufficiently strong for most purposes. Don't forget about wood. Wood is strong, flexible and light.
 * It has to be easy to add new parts to it. By using one size of PCB you can drill holes ahead of time. And you'll be able to stack PCBs. If you're familiar with Meccano sets you know the advantage of using one standard hole size and spacing. Picking one for your robot can make adding parts very easy and fast, of course this is less efficient with space.
 * It has to be easy to remove parts of it: Make sure you can access any of its parts without having to take most of the robot apart. Especially batteries should be accessible.
 * It has to be in balance. The weight of the robot should be mostly within the figure formed by connecting the wheels of the robot (A triangle for 3 wheeled robots, a rectangle for 4 wheeled robots). Placing significant weight outside this figure makes it more easy for the robot to tip over. The center of gravity should also be as low as possible, otherwise the robot could tip over when turning too fast.
 * It has to have a size that's practical: Don't make it too small or you end up with insufficient space for all the features you had in mind. Don't make it too large either or you end up with a robot that can't maneuver without bumping in furniture and people. Or worse: can't get through a door post.
 * Avoid putting the wheels directly on the motors' axles. Use an axle and connect the motor to it with gears. For small robots this isn't important, but larger would displace the axle inside the motor and damage it.