In electric rc cars, a mechanical speed control (MSC) is one way of controlling how fast the engine is going -- the other being an electronic speed control. It works like this: you have a servo that essentially drives the arm of what is effectively a potentiometer. When the servo pushes the link to the mechanical speed control forward, the resistance is reduced, and so the current running to the electric motor is increased and the vehicle goes faster. However, there are a number of drawbacks to this approach:

  • Usually mechanical speed controls only have a fixed number of possible speeds. For example, the common MSC used in Tamiya vehicles is 3 forward/2 reverse.
  • Setting up the linkage to the servo is a pain.
  • It wastes precious power in the resistors that are used to reduce current.

So somebody smart realised that you could connect the output from the receiver directly to an electronic device that would control current flow to the electric motor directly, and hence, avoiding the mechanical stage, be faster, more efficient, simpler and provide true proportional control. Hence the electronic speed control.

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