Electronic Speed Control. This is the most important component. It controls the motor speed but in a Meccano model it can do so much more. You can use 2 ESCs and no servo if you like. Imagine a Meccano tank or bulldozer. One motor for each track, each motor controlled by a separate ESC. For this you would use a joystick transmitter. I could operate my Meccano Etch-a-sketch with this. Now it's a bit hard to see in my photo, but the ESC has 3 wires that go to the Receiver unit then a pair of heavy duty wires for DC in and another pair for DC out.