Please note: this article is incomplete and in development.
The speed control is your connection to the powerplant of your electric powered vehicle. Not only does it control how fast you go, but in racing, it is more important how well you can control the vehicle at lower speeds.
There are two basic ways to regulate speed of your R/C, a mechanical speed control or an electronic speed control.
Least expensive and often provided with kits is the mechanical speed control, which regulates the voltage sent to the motor by way of electrical resistors. A second servo is used to push a sliding switch over three or four metal tabs connected to the resistors. Each tab provides a different amount of resistance, controlling the speed of the motor. Some MSC's don't use this method; they use a length of resistant wire wrapped around a block and the same switch tab slides across the wire. The farther along the wire the tab is, the more resistance and slower the vehicle goes. This is a slightly smoother control than the three-position types. Both types have a final position in their movement that reverses the voltage and provides reverse for the vehicle.
This is a highly inefficient method of controlling speed. There is a lot of resistance between the battery and the motor, and MSC's often self-destruct by getting so hot they melt any solder joints. They are very hard on batteries, have limited control, the increased resistance reduces the run time you will get out of the battery, and most importantly, not all of the power gets to the motor, which means for any given battery or motor - you are not going as fast as you could.
Electronic speed controls change everything. ESC's use a bank of Field Effect Transistors (FET's) to regulate the speed by generating high-frequency pulses of voltage to the motor based on the signal sent to the radio from the transmitter. The result is a smooth accelleration curve from stop to full throttle. ESC's have as little as 0.00034 ohm resistance at full throttle; there is very little loss of electricity from the battery to the motor. Any model of vehicle will run faster, run longer, and have throttle response unparalleled by any MSC.
Racing level ESC's do not have a reverse function, they have an internal electrical system that emulates brakes. Using a high-frequency "shunt" (basically shorting across two of the motor armature poles,) the ESC stops the motor and holds it stationary, effectively locking up the wheels. During this braking phase, electricity is fed back to the battery, providing a mild "regenerating" or "recharging" effect. Many sport or entry model ESC's do have reverse functions, but they are not legal to use in racing events.
ESC's are available for any budget, ranging from under $50 to several hundred dollars. When selecting an ESC, be sure to select a model that will safely run the number of cells in the battery pack you plan to use and the turn of motor you plan on using. While most ESC's will survive stepping outside these specified limits, some will not and it would certainly void any warranty on the ESC.
. . . to be continued . . .
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