Although passive attachments can be very helpful, sometimes robot attachments need a bit more horsepower. By adding power to the robot attachments, you add a wide range of new functions that your robot can perform, such as grabbing, lifting, triggering, and even pushing. On the EV3 brick, there are only four power outlets, and for most robot designs, two of the outputs will be used for navigation. This leaves only two power sources for attachments, so you must use them wisely. Just like with the passive attachments, the idea of having a common interface for fast attachment switching is important. There may be times when you have missions that need a claw attachment and later you find the need for an attachment to lift an object. These attachments need to connect to the EV3 motor so that they can be switched quickly with very little effort. Later in this chapter, I’ll discuss some common interface designs.