I want to put more engines, how can I do that?
Multiplexer for NXT / EV3 engines (NXTMMX-v2). This product allows you to connect two motors and one sensor to a single sensor port.
You can connect it to any of the four sensor ports on the NXT or EV3. The NXTMMX has a sensor port itself, so you can attach a sensor or other devices to mark. You can connect the NXT or EV3 motors to the motor port.
Note that this will require an external power supply, the brick sensor port does not provide enough power to drive the motors. It can be used with NXT, EV3, EVShield and PiStorms. It is supported in EV3G, NXT-G, NXC, RobotC