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This is part of a series of articles put here, written by me to try and
explain electic flight to a newcomer. These articles are taken from the
spad combat
forum
in the electric section.
ESCs
Firstly, why do we need an ESC? Well, there are two different types of
ESCs:
Brushed motor
ESCs
For brushed motors, there is only one reason. Without an ESC, you could
hook a brushed motor directly to a battery and let it scream away on
full throttle with no control over its speed. In this case, the ESC
acts like a throttle servo. It plugs into the throttle channel of your
RX and regulates the speed of the motor.
Brushless motor
ESCs
For brushless motors, the ESC has to perform two functions. Firstly, it
needs to regulate the speed, just like a brushed ESC. Secondly, it has
to switch polarities to keep the motor spinning. Remember how a brushed
motor mechanically switched the direction current travels in every time
it turns round? Well there’s no brushes in a brushless motor
(duh) so the ESC does the switching electronically.
Most ESCs also include a battery eliminator ciruit (aka BEC) which
supplies a clean 5 volts to the RX no matter what battery voltage goes
in.
The Theory (cue
scary organ music)
The switching and throttle regulation works using FETs. These are
basically big transistors, and they switch on and off extremely fast to
produce different voltages. For example, if you have a 10 volt battery,
but you only want 5 volts to go to the motor, you could do this with a
bit of maths and a big resistor. Unfortunately this means that half of
your energy is wasted as heat in the resistor. Not good for battery
life.
If you have ten volts into an ESC and want 0 volts out, you turn off
all the FETs. If you want 5 volts out, you turn the FETs on and off
very quickly so they are on 50% of the time and off 50% of the time.
This creates an average voltage of five volts, which is what you want,
and then it is smoothed out by a capacitor to give and effective five
volts. You can do this with any voltage you want (as long as it is the
same as or less than the input voltage) by flashing the FETs on and off
for different lengths of time. And as we all know, more voltage drives
more current = more power, so a higher voltage equates to a higher
throttle setting.
Disclaimer
I don't claim to be an expert. All of this information is offered on an
"as is" basis. All text here is hereby released under the GNU FREE
DOCUMENTATION LICENSE for anybody to use, copy or alter, commercially
or otherwise, as long as, AND ONLY AS LONG AS THIS TEXT IS PRESERVED.
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Email: rcpoweruk@gmail.com
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