Building modular robot hardware
Modularity is the key to enabling efficient testing of subcomponents to avoid the potentially frustrating experience of Big Bang Integration. This is true for hardware and software, and for the hardware it applies to both the mechanical as well as electrical components of your robot.
Mechanical components
Problems with the mechanical subsystems of your robot, such as the wheels with their motors or a gripper mechanism, are typically the easiest to troubleshoot. Issues like too much friction, overheating, or a motor turning in the wrong direction are easy to spot without dedicated tools. In addition, the mechanical components of your robot will usually be quite modular in nature without having to put too much thought into them.
Especially during the development phase of your first robot prototype, it is best to keep all mechanisms as simple as possible to make it easy to spot where a particular problem comes from. Ideally, you have a dedicated...