Electronic Speed Controller Refresher.
Speed Control Features, Just for kicks! I get calls throughout the day asking me certain questions.
We will briefly examine some of them here; with Matt customer service "Guy" :P
Brake
A brake forces the motor to stop turning once the speed control stops delivering power. Electric motors become generators when being driven by their output shaft (for example, by a wind-milling propeller). The more load you put on a generator, the harder it is to turn. A speed control brake simply places a load (a low resistance) across the motor terminals, making it difficult for the motor to turn. This is generally sufficient to stop it completely. If a folding propeller is being used, this will allow it to fold. If a fixed propeller is being used, it will produce less drag than if it were spinning.
Soft Start
This term describes both speed controls and a special kind of on/off-only motor switch. In both cases, it indicates that the control will go from off to full throttle slowly (for example, over the course of one second) instead of instantly. This is very important if using a gearbox or folding propeller, since an instant start can strip gear teeth, or shear propeller hinge pins. Some speed controls let you adjust the soft start time interval.
Digital or Microprocessor
Until fairly recently, the majority of speed controls were analog, meaning they worked with voltages and pulse widths, and had dedicated circuitry to perform each of their functions. Most modern speed controls are digital. These controls use a microprocessor to measure the incoming pulse with from the radio, and to generate the pulses to the MOSFETs. Digital designs have the advantage of being adjustment free, and of being able to provide sophisticated safety features. For example, most digital controls will refuse to turn on until the throttle stick has been moved completely to off first.
Battery Eliminator Circuit (BEC)
In small planes, it is advantageous to eliminate the weight of a receiver battery. Many speed controls provide a BEC feature that provides power to the receiver and servos from the motor battery. There is still a great deal of debate as to whether this is safe, primarily due to the danger of electrical noise getting into the receiver and causing reduced radio range. The other danger of course is that the motor battery could run down to the point that the BEC cannot provide power to the receiver. BEC is very popular with the electric pylon racing crowd, where the planes never get very far away, and land immediately after the race.
Automatic Cut-Off
This feature is generally used with a BEC, so that the motor will shut down before the battery is depleted, thus reserving some power for the radio.
Optical Isolation
To reduce the possibility of the speed control interfering with the radio receiver, some controls use an optoisolator chip. This is basically an LED (light emitting diode) and photo-transistor encased in plastic. The signal from the receiver drives the LED, which optically transfers the signal to the rest of the speed control. There is no electrical connection between the receiver and the main part of the speed control. Obviously, this eliminates the possibility of providing a BEC.
I hope this will reduce some questions you might have. I'll try to touch on subjects we can all use a refresher course. I hope you are all enjoying Motion RC, our hope is to "Give Back" to our customers the best way we can. Information is always free and helps everyone to learn!
We will briefly examine some of them here; with Matt customer service "Guy" :P
Brake
A brake forces the motor to stop turning once the speed control stops delivering power. Electric motors become generators when being driven by their output shaft (for example, by a wind-milling propeller). The more load you put on a generator, the harder it is to turn. A speed control brake simply places a load (a low resistance) across the motor terminals, making it difficult for the motor to turn. This is generally sufficient to stop it completely. If a folding propeller is being used, this will allow it to fold. If a fixed propeller is being used, it will produce less drag than if it were spinning.
Soft Start
This term describes both speed controls and a special kind of on/off-only motor switch. In both cases, it indicates that the control will go from off to full throttle slowly (for example, over the course of one second) instead of instantly. This is very important if using a gearbox or folding propeller, since an instant start can strip gear teeth, or shear propeller hinge pins. Some speed controls let you adjust the soft start time interval.
Digital or Microprocessor
Until fairly recently, the majority of speed controls were analog, meaning they worked with voltages and pulse widths, and had dedicated circuitry to perform each of their functions. Most modern speed controls are digital. These controls use a microprocessor to measure the incoming pulse with from the radio, and to generate the pulses to the MOSFETs. Digital designs have the advantage of being adjustment free, and of being able to provide sophisticated safety features. For example, most digital controls will refuse to turn on until the throttle stick has been moved completely to off first.
Battery Eliminator Circuit (BEC)
In small planes, it is advantageous to eliminate the weight of a receiver battery. Many speed controls provide a BEC feature that provides power to the receiver and servos from the motor battery. There is still a great deal of debate as to whether this is safe, primarily due to the danger of electrical noise getting into the receiver and causing reduced radio range. The other danger of course is that the motor battery could run down to the point that the BEC cannot provide power to the receiver. BEC is very popular with the electric pylon racing crowd, where the planes never get very far away, and land immediately after the race.
Automatic Cut-Off
This feature is generally used with a BEC, so that the motor will shut down before the battery is depleted, thus reserving some power for the radio.
Optical Isolation
To reduce the possibility of the speed control interfering with the radio receiver, some controls use an optoisolator chip. This is basically an LED (light emitting diode) and photo-transistor encased in plastic. The signal from the receiver drives the LED, which optically transfers the signal to the rest of the speed control. There is no electrical connection between the receiver and the main part of the speed control. Obviously, this eliminates the possibility of providing a BEC.
I hope this will reduce some questions you might have. I'll try to touch on subjects we can all use a refresher course. I hope you are all enjoying Motion RC, our hope is to "Give Back" to our customers the best way we can. Information is always free and helps everyone to learn!
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