of the many advantages of electric flight is that we can tap into
the main battery pack to supply power for the receiver and servos.
Most Electronic Speed Controllers (ESCs) have a built-in Battery
Eliminator Circuit (BEC) that eliminates the need for a separate
receiver battery pack - thus reducing weight and adding the convenience
of recharging only a single battery. The BEC is fed by the main
flight battery and drops the voltage to a level that is suitable
for the receiver and servos. This regulated output, typically 5v
or 6v, is commonly fed from the ESC to the receiver via the control
cable to the throttle channel. The receiver + and - bus then feeds
the power to each servo so it is not necessary to connect to the
receiver's battery input connector, if it even has one.
function of the regulation is to supply a steady voltage to
the receiver and servos while the main flight pack is drained
in flight. If the flight pack voltage becomes too low, the Low
Voltage Cutoff (LCV) feature of the ESC will turn off the motor,
saving the rest of the battery power to continue feeding the
receiver and servos for a safe landing.
scenario described above is most commonly seen in parkflyers using
up to 3-cell (11.1v) Lithium flight packs as the linear regulators
in the BEC are not designed to handle more than 12 volts. What alternatives
are available for higher voltage power systems? Why not just use
a receiver battery like those used in glow-powered planes? What
else can I do with an on-board regulator? In this month's issue
of AMP'D, we explore the need and advantages of why we use regulated
Choosing A Regulator
are available in many sizes, both physically and functionally.
Most can handle input voltages of 2s to 3s LiPo. Some can
handle input voltages up to 6s or 10s LiPo or higher. (1s=1cell=3.7v)
typical regulator output will be 5v or 6v or selectable for
either voltage. The advantage of using 6v on many servos is
to increase the transition speed and torque. A 6v output is
often used in 3D applications where quickness and precision
of flight are needed. Note that not all receivers or servos
are capable of handling a 6v supply.
parkflyer and indoor models will almost always use a BEC that is
part of the ESC. Weight is more critical in these smaller planes
and most of them use 2 or 3 cell LiPo packs with a few servos. In
cases where many servos are used, like full-house controls, retracts,
or flaps, it is possible to exceed the capabilities of the linear
BEC equipped ESC.
new CC BEC from Castle
Creations is a little device that eliminates the need
for a receiver and servo battery pack. It draws higher voltage
from the motor batteries and drops it to a voltage level
that is suitable for your receiver and servos. This is required
in applications which draw high power for multiple servos
or use more than 3-cell LiPo packs, as most ESCs with linear
BECs are not designed for these more demanding applications.
BEC is a flexible design that can be used for many applications
requiring a regulator. The switching regulation design, as opposed
to a linear regulation, allows it to maintain a small package size
and weight while providing up to 10amps of peak current. The input
voltage can range from a 2s to 6s Lithium battery. The output voltage
can be programmed from 4.8v up to 9v. As noted above, not all servos
and receivers can handle more than 5v so you must check with the
manufacturers specifications before using a higher supply voltage.
has a series of regulators called ParkBEC
The ParkBEC series comes in 5v and 6v versions which allow
you to run more servos on input voltages up to 8s LiPo. Weighing
in at only 6.2 grams (0.22oz), these regulators are the smallest
and lightest switching BEC on the market - providing a great
enhancement for smaller 3D and heli models.
SportBEC offers additional capability over the ParkBEC at about
twice the weight. Because it is an efficient switching regulator,
SportBEC can supply its full rated current of 3.5A all the way up
to a 8s input voltage. As many as 8 servos can be powered without
worrying about an overheating BEC. SportBEC works great up to very
high voltages, and is especially suited for "sport" aircraft
and glow conversions. SportBEC is usually a necessity at 4s and
above when running high torque or digital servos. SportBEC's output
is selectable between 5V/6V using a small slide switch. The 6V setting
gives more speed and torque to the servos, and is especially useful
for helicopter flyers. A red LED indicates when 6V is selected.
installs between your ESC and receiver, so you don't have to modify
your speed control to disable its internal BEC.
What is a UBEC?
many years, the only option available to eliminate the receiver
pack on a glow to electric conversion was the UBEC.
The Ultimate BEC (or UBEC) is an external circuit that taps
power from your battery pack and regulates the voltage to
5 or 6 volts to power your receiver and servos. It does
not replace the speed control, however, it replaces the
BEC function in a non-Opto-isolated speed control with much
more capabilities or it provides the BEC function in any
UBEC versions are available to handle input voltages up
to 35v (10s LiPo) or 45v (12s LiPo). They have either a
5v or 6v output rating of 3 amps continuous and up to 5
amps for 5 minutes which can power up to 8-10 servos.
A UBEC allows you to
use your flight pack to supply power for your radio and
The "UBEC" has a set of input and output leads.
The input leads are soldered on the input side of the speed
control at the battery connector. The output lead plugs into
the receiver where you would normally plug a receiver battery.
The last thing to do is to disable the BEC function of your
speed control if there is one. This is usually accomplished
by pulling the red pin out of the servo lead on the speed
control. Note that Opto-isolated ESCs do not have a BEC so
there is no need to pull out the red pin.
most .40-size to .90-size models, the UBEC provides a lightweight
alternative to using a receiver battery. It also eliminates
the need to remember to recharge the receiver battery.
Linear or Switching Regulation
voltage regulator is an electrical circuit designed to automatically
maintain a constant output voltage level even when the input
voltage changes. In our applications, we use the main flight
pack to power the regulator and expect a steady output of
5v (sometimes 6v) to feed our receiver and servos. When this
function is built into an ESC, we call it a Battery Eliminator
Circuit (BEC) because it eliminates the need for a separate
receiver battery pack.
regulators are based on devices (usually one or more transistors)
that operate in their linear region. Linear regulator designs have
the advantage of very "clean" output with little noise
introduced into their DC output, but are less efficient and unable
to step-up or invert the input voltage like switched supplies. A
typical BEC in an ESC, being a linear regulator, can only handle
input voltages up to a 3s LiPo (11.1v) and can only deliver regulated
power to the receiver and a few servos. The linear BEC is an inexpensive
feature to add to an ESC and satisfies the majority of smaller electric
regulators rapidly switch a series device on and off. The duty cycle
of the switch sets how much charge is transferred to the load. Because
the series element is either fully conducting, or switched off,
it dissipates almost no power; this is what gives the switching
design its efficiency. Switching regulators are also able to generate
output voltages which are higher than the input voltage ? something
not possible with a linear design.
comparing linear vs. switching regulators, the two types of regulators
have different advantages:
Linear regulators are best when low output noise is required
Linear regulators are best when a fast response to input and output
disturbances is required.
At low levels of power, linear regulators are cheaper.
Switching regulators are best when power efficiency is critical.
Switching regulators are required when the only power supply is
a DC voltage, and a higher output voltage is required.
At high levels of power (above a few watts), switching regulators
the past, our receivers were more prone to being interfered with
by switching regulator noise. Newer dual conversion and 2.4GHz spread
spectrum designs have greatly reduced the potential for interference.
Further, newer switching regulator products like the SportBEC and
CC BEC are designed to ensure they do not create radio interference.
Components like shielded inductors and an optimized layout reduce
the radiated noise so you can use it without fear of glitching.
more detailed information, visit "Voltage
Regulators" on Wikipedia.
Gas, Jet, Electric, or Glow
the power source of your R/C airplane is not electric, you
will need some sort of receiver battery. When the electric-powered
model is big enough or expensive enough, most people consider
using a separate power system on the receiver and servos
for better safety. If you have a larger model with many
servos, particularly digital servos that use a lot of current,
you need a reliable power source of high capacity.
Duralite Regulators come with a failsafe switch that is
pre-wired and ready for use. Should the switch or the wiring
between the switch and regulator fail, the regulator will
stay in the "on" position and continue providing
power to your radio and servos. This type of design is essential
for large aircraft safety and protects your investment in
Regulator is designed to operate on input voltages from
5 to 12 volts, allowing you to power your receiver and servos
with a high capacity, yet lightweight, Lithium Ion or Lithium
Polymer battery pack.
flying larger, more powerful aircraft, it is also important
to use redundancy in the receiver and servo power design.
High capacity battery technologies like Lithium-Ion are
used to provide 6-10 flights before requiring a recharge.
Built-in safety circuitry insures that each cell in the
battery pack stays in balance when charging.
Key features of the Duralite PLUS System
& Powerful - constant voltage to servos
Energy Density - Long Cycle Life
in Pack Redundancy - Available In all 4 & 6 Cell
Memory & No cycling - Easy to Use
Robust than Li-poly's - Cylindrical design can better
withstand impact & vibration
Discharge Continuous - 2C
lead system - choice of power output leads/connectors,
plus charging lead w/yellow connector
creates a safety margin where if there is a problem with any
cell in a pack, the pack will continue to operate at half of
the packs rated capacity, at normal voltage. The larger and
more powerful Duralite PLUS 4-cell packs are assembled with
two 2-cell packs in parallel (2s2p). This paralleling creates
"in pack redundancy" with four cells working together
to allow higher current output for larger, more powerful aircraft.
Big Power / Big
"Power Force" VRLI2 Voltage Regulator from FMA
Direct is designed specifically for powering high current
flight electronics (receivers and servos) in radio controlled
aircraft. It can be used in sport, giant scale, electric
planes and helicopters. It is ideal for use in aircraft
with dual radio systems and outputs are user selectable
for either 5v or 6v. This extremely low dropout regulator
maintains a maximum 0.15v drop, even if the battery voltage
decreases under full load.
VRLI2 supplies up to 10amps continuous current which is sufficient
for driving many high torque servos.
Status LEDs provide a quick indication of battery condition.
The VRLI2 includes an on/off switch with failsafe operation
and will not drain the battery when switch is off. Since the
VRLI2 is a linear regulator, it produces no noise interference
and can safely be used with older receiver technologies.
dual-battery regulators from Smart-Fly
provide the user with battery redundancy and a remote fail-safe
provides the user with battery redundancy and an adjustable
regulator output from 5.2 volts to 6.5 volts. An optional
remote failsafe switch can be used in aircraft with engines
up to the 100cc size. The SuperReg combines several features
into one lightweight unit. It has dual battery inputs with
isolation between the two batteries. In case of a catastrophic
failure of one battery the other can continue to supply
power to the aircraft. All power input and output connectors
are Deans Ultra Plugs to handle up to 7.5amps continuous
SuperReg also has failsafe operation with the optional remote
on/off failsafe-switch. The switch turns the failsafe regulator
on but does not carry the system load current. If the switch
or wiring between the switch and failsafe regulator were
to fail the regulator stays on until you unplug it from
is similar to the SuperReg but can supply a whooping 17.5
amps continuous current when the input voltage is 8.4 volts
and the regulator is set to an output voltage of 6.0 volts.
The TurboReg also uses a computer-grade brushless fan to
provide active cooling of the regulator.
Regulators in Action
need to keep multiple Rx. battery packs charged.
can be used in many other functions besides providing
power to the receiver and servos.
using dual UBECs, one UBEC can provide 6v to the receiver
and servos while the second UBEC provides 5v for the retract
servos. In this manner, the control surfaces will have
the benefit of higher torque and speed from the 6v, 20
gram, UBEC and the added safety from the isolation of
a retract jam. Most retract servos require a 5v supply
and will not tolerate 6 volts.
a tip from Team Futaba's Dan Landis, I installed dual 10-amp
Power Force regulators to provide more current to the dual
rudder servos on my 33% Hangar 9 Edge 540. The regulators
are positive controlled and they will work fine with common
ground. Since they are push type only, they can also be
paralleled on the positive side too. The second regulator
tip from Dan is an easy solution to eliminate blowback on
my two rudder servos.
Dual regulators means
more servo power!
Light 'em up at night!
and other illuminating products like this Night-Light
Set for the Wingo are becoming very popular. By adding
external regulators like the new CC
BEC or ParkBEC
to an airplane, you can power many lights on the wings,
fuselage, and tail for some night flying fun!
it comes to small slowflyer and parkflyer models, we will almost
always use the BEC built into the ESC. Weight is at a premium
in these planes, and since most of them use two or three LiPo
cells with several micro-servos, the inexpensive, low-noise, linear
regulators are well within the capabilities of even the smallest
ESC. Exceptions to this scenario might be needed by a 3D pilot
wanting the servos to run on 6v for more speed and torque, or
a full-house scale model with extra servos.
sport and scale aircraft also benefit from a BEC on non-Opto-isolated
ESCs but it is possible to exceed the manufacturer's recommendations
regarding cell count, maximum number of servos, or servo current.
In this situation, or when using an Opto-isolated ESC, you must
either use a separate receiver pack or take advantage of a more
capable external BEC. Switching regulators are best when power
efficiency is critical since they weigh less than linear regulators
and accept a wider input voltage range.
sport and scale models typically need a BEC because the
ESCs do not allow use of the BEC with more than 3 LiPo cells
or they use an Opto-isolated ESC that does not have the
BEC. When the model becomes sufficiently large or complex,
safety is a main concern.
these photos of a turbine-powered T-bird, a voltage regulator
can be seen on the left and the Spektrum DX-7 receiver with
4 JR MatchBoxes to run 11 digital servos and the main computer
(ECU). The Duralite PLUS 4-cell pack creates "in pack
redundancy" with four cells working together to allow
higher current output for larger, more powerful, or complex
safety in larger or giant-scale models is obtained though
redundancy, high-capacity battery technology, and fail-safe
operation. New technologies like spread spectrum radios
in the 2.4GHz frequency band offer even further safety from
anti-jamming features, greater noise immunity, and reducing
user error by forcing a match between the model and the
you fly electric, fly clean, fly quiet, and fly safe!
Duralite PLUS 4-cell pack redundancy
Turbine-powered Jet Complexity
section of AMP'D covers some of the questions that our
readers have sent in and I thought would be interesting
W. asks: "Hi Greg, I have a DX7 with the Ar7000
and running 4 DS821 and 1 JRes539 so five servo's in
my H9 Funtana 50. With the supplied 1100mha flight pack,
how will this battery handle the load as I have read
alot of threads about recievers unbinding due to power
problems? I have not flown this plane yet and am test
flying the receiver in my foamy to check for any range
As long as the receiver battery stays above 3.5v
you won't have any problem with the AR7000. In
other words, you need to keep the 4-cell 1100mAh
NiCd pack charged to stay out of trouble.
all your components can handle a higher voltage,
you can also try a pack with both higher voltage
and capacity like the new Spektrum 2700mAh 6.0v
NiMH pack (right).
you are flying with electric power, you can eliminate
the receiver battery along with the weight and
charging issues by using an external BEC.
L. asks: "Hi Greg, What a great article. Just what
I've been looking for. My next question is "How
do I get copies of Issue's #1 and #2"? Thanks a
Thanks for the kind words. We are getting many
requests for a printable version of the columns
so I will now create a PDF file of each issue
and put a printer image at the bottom of each
column that you can click on.
get PDFs of the first three columns, you can
use these printer icons here.
questions by e-mailing me at email@example.com
section of AMP'D reveals some of the feedback or suggestions
that our readers have sent in about previous issues.
most recent RC Universe column, "AMP'd - issue
3, December 2007 that starts with -- What Motor do I
use?" is probably one of the best electric articles
I have come across to date. Between your comments along
with the many references to additional data, this has
to be something that electric modelers should keep on
their PC desktop for constant referrals. I have every
intention of mentioning this specific article in my
next available FAQ column that appears monthly in Model
Aviation. Great work!
Aberle, AMA 215
suggestions by e-mailing me at firstname.lastname@example.org
Silver Series High Power
Brushless ESC For Large Electrics
Silver Series Brushless ESC Programming Card
Print Issue 4 "Why Regulate?"