104 MODEL AVIATION
THIS COLUMN OFFERS one meet
announcement, describes an Electric built to
meet a design challenge, and reviews a
variety of new and classic reader questions.
Colin McKinley—an E-modeler friend from
long ago—wrote to announce an Electric funfly
hosted by the Riverside Aero Modelers. It
is scheduled for August 23-24 in King, North
Carolina—near Winston-Salem. Not all of the
details are finalized as I write this, but they
will be by the time you read it.
You can get full info from Contest
Director Randy Covington at (336) 983-9126
or [email protected]. You can
also write to Colin at 4003 Poindexter Ave.,
Winston-Salem NC 27106. When you see
Colin at the meet (he’ll be the guy flying
numerous vintage Radio Control [RC] Econversions),
be sure to tell him Bob sent ya!
As described in recent columns, last summer
brought to my attention some special
difficulties would-be E-aeromodelers can face
trying to get started in this hobby. These
particular problems were largely associated
with (i.e., because of) products peddled as
Almost Ready-to-Fly (ARF) “trainers” that
were anything but.
At that time I was trying hard to help some
people in this situation, and I began thinking
about all of the things I’ve seen happen with
first-timers at the stick—for more than 40
years. Having flown RC since the mid-1950s,
I did not need a basic trainer but was
motivated by observing some people who did.
This resulted in a design challenge for
me—just for the fun of it. I wondered about
ways to approach this need and set about
some design goals for a compromise
beginner’s design. The result, shown in some
photos, is “Stikum.”
Stikum is somewhat a large park flyer
conceptually, but it really needs a regular
flying field. (I have some reservations about
anyone learning to fly anything in parks; they
are generally too public, and safety is a
concern.) The Stikum’s design puts it in the
middle, between smaller park flyers and
larger wet-power trainer models that are
popular at many club fields. I feel that Stikum
can fit in a bit better in a wider range of
venues.
Stikum is patterned in part after the
Revolt! (featured in the 11/94 MA); it has the
same airfoil and a 600-square-inch wing,
although it’s more lightly and simply
structured. The same is true for the built-up
tail surfaces. The fuselage is clearly
different—inspired by some popular park
flyers.
Bob Kopski, 25 West End Dr., Lansdale PA 19446
RADIO CONTROL ELECTRICS
An overview of Stikum: a docile Electric model that is rather hard to damage. Nearly
everything “gives” a little during a mishap, minimizing breakage.
Detail of the motor mount and motor-plate attachment; two brass straps, four screws,
blind nuts in the motor plate secure the latter to the fuselage boom.
Dual 1⁄8 light plywood pylon verticals, 1⁄8 balsa saddle plates, 1⁄4 through wing dowel form
wing mount. The seven-cell pack is Velcroed underneath it all.
airplane wiring. This connector set is also the
“switch”; everything is powered when the
pack is plugged in.
To further accommodate those hard first
landings, the geared Astro 05 is mounted on a
field-replaceable 1⁄8 birch plywood “break-off
plate.” The idea is for this specific piece to
fail before any other part of the fuselage
structure does. This motor plate is firmly
clamped to the 1⁄2-inch square white pine (or
spruce) fuselage boom with screws and small
metal plates.
The motor, nested in a “V” block, is
clamped to the plate using Gold-N-Rod inners
and 2-56 machine screws. There is no glue
used in this area, so a spare plate and a
screwdriver can easily get your model back in
the air following a mishap.
Given that an 11- or 12-inch wood
propeller is usually strong and that just it
striking the ground could cause a motor-plate
failure, I chose a Master Airscrew 12 x 8
folder with the hub screws snugged a bit—so
the blades don’t flop around. Here, the
propeller is not intended (and not wanted) to
be a normal folder, but a propeller with blades
that can yield backward instead of holding
firm during a propeller strike.
The 1⁄8-inch-diameter wire landing gear
(with fairly large, light wheels) is somewhat
springy but holds up well during takeoff and
landing rolls. This assembly also tends to give
rather than bend or break free. This works
because whatever Stikum does it does
slowly—assured by the low all-up weight (49
ounces), large wing, and thick wing section
(121⁄2%). Typical liftoff from mowed grass is
20-30 feet, and not much forward speed is
needed to accomplish it.
One goal I did not reach was my design
target of 48 ounces all up. The extra ounce
can be blamed on my using my own-design
Sport Speed Control (9/99 and 10/99 MA),
which is heavier and more bulky than almost
any contemporary commercial Electronic
Speed Control (ESC). In any case, a BEC
(Battery Eliminator Circuit) saves the weight
of a radio battery—part of the original
planning.
One interesting (for me) and exciting (for
him) field experience came about when I
offered a beginner—who had only flown a
small Electric by hand launching a few
times—the opportunity to ROG Stikum. He
reluctantly, nervously tried it. His first attempt
failed because of steering fumbles, but the
model got off easily thereafter; he was
smiling ear-to-ear.
Once airborne, the beginner seemed to
find himself immediately comfortable with
Stikum; I think because this is one of those
airplanes that flies “slower than the speed of
thought.” I think he would have bought
Stikum on the spot were it available!
Contrary to what one might think, a
skilled pilot can fly Stikum in rather breezy
conditions. But then a skilled pilot would
likely not want a Stikum, right? Wrong!
What began as a design challenge for
me—a fun experiment of sorts—has yielded
an easygoing, rather lazy, land-at-your-feet
flier that has brought requests for plans from
the local flightline—a completely unexpected
outcome. The finger-pointing chuckles I
expected when I first brought Stikum out
never happened. This easy-to-build, low-cost
project has turned out to be an appealing,
docile, nice-flying E-aeromodel. Serendipity!
(That might be a better name than Stikum!)
I recognize that this design is not the best
for every early training need. No model can
be. It lies somewhere between a small, calmair-
only park flyer and a howling-hog 40 wet
machine. The Stikum concept is just another
approach—another option—perhaps
appealing to some and unappealing to others.
However, it does illustrate what can happen in
pursuit of a challenge. Maybe it will give you
some ideas of your own.
No matter how much some topics are
covered, there are always newcomers with the
same questions and/or those who know they
read something somewhere but need a
refresher. And every now and then, along
comes a never-before-asked reader question.
Following are some new and some longrunning
topics of reader inquiry.
My recent columns have waxed hard on
the chokes topic, and several readers have
come up with the same question: “Do chokes
have direction?” No! Chokes are like resistors
in this respect; you can use (connect) either of
the two leads either way. Chokes have no
“polarity.” For the sake of completeness,
106 MODEL AVIATION
some electronic components do have
direction or polarity, such as all
semiconductors (e.g., diodes) and most (but
not all) electrolytic capacitors.
Since many ask, it is impossible for me to
easily copy columns and send them to you.
This recurring request apparently comes
from my frequent references to earlier
column topics. However, you can get article
reprints from AMA Headquarters. Unless I
make a specific offer of such (e.g., Universal
Slow Charger Parts Update), please don’t put
me in the position of having to say no; I
much prefer reader letters to which I can say
yes or make some other positive reply!
Another common reader query involves
multimotor installations. Beginning with
two-motor (twin) systems, following are
some basic guidelines. Two (brushed) motors
can be wired in parallel or series. In either
case, only one speed control is generally
needed. (Extremely large power systems may
need multiple ESCs, and brushless systems
typically have separate, noninterconnected
motors/controllers.)
“Parallel” means that both positive (+)
motor terminals are wired together, and both
negative (–) motor terminals are wired
together, and that is how they are wired to
the ESC. “Series” means that the positive (+)
terminal of one motor is wired to the
negative (–) terminal of the other. Then the
negative (–) terminal of the first and the
positive (+) terminal of the second are the
108 MODEL AVIATION
final or overall motor terminal connections;
these are what the ESC drives.
Two motors wired in parallel consume
twice the current of a single motor—all
other conditions being equal. Both motors
would “see” the same applied voltage (cell
count) as either would as a single motor.
A pair of motors wired in series have the
same current flowing in each, and this
current would be the same value as if with a
single motor. However, the two-motorseries
combination requires twice the
applied voltage (cell count) as a single
motor.
In either case, for a given individual
motor power level and running duration, the
battery weight in a twin is nominally double
that of the single motor case. This is
because for parallel motors drawing twice
the current of one, cells of twice the
capacity (and nominal weight) would be
indicated. Series motors tend to suggest
twice as many of the same capacity cells as
for one motor—again, twice the battery
weight.
Other considerations involve the ESC
requirements. Parallel motors, with twice
the current demand, dictate a highercurrent-
capability ESC. Not only that, but
doubling the system current can have
implications on wire gauge, switch and fuse
ratings, and connector considerations.
My “dividing line” is somewhere
between 10 and 15 amps per motor. I’m
more inclined to use parallel wiring at the
lower end of the range (with 10-amp Speed
400s and smaller) and series wiring at and
beyond the upper end of the range—say,
with motors normally running 15 amps and
higher singly. This is my guideline for sport
flying—not a hard-and-fast capital rule for
application. Next month I’ll consider the
more-than-two-motor case.
Thus ends one more column. Please
include an SASE with any correspondence
for which you’d like a reply. Everyone so
doing does get one! And do enjoy the
refreshing delight that early springtime
Electric flying brings! MA
Edition: Model Aviation - 2003/05
Page Numbers: 104,106,108
Edition: Model Aviation - 2003/05
Page Numbers: 104,106,108
104 MODEL AVIATION
THIS COLUMN OFFERS one meet
announcement, describes an Electric built to
meet a design challenge, and reviews a
variety of new and classic reader questions.
Colin McKinley—an E-modeler friend from
long ago—wrote to announce an Electric funfly
hosted by the Riverside Aero Modelers. It
is scheduled for August 23-24 in King, North
Carolina—near Winston-Salem. Not all of the
details are finalized as I write this, but they
will be by the time you read it.
You can get full info from Contest
Director Randy Covington at (336) 983-9126
or [email protected]. You can
also write to Colin at 4003 Poindexter Ave.,
Winston-Salem NC 27106. When you see
Colin at the meet (he’ll be the guy flying
numerous vintage Radio Control [RC] Econversions),
be sure to tell him Bob sent ya!
As described in recent columns, last summer
brought to my attention some special
difficulties would-be E-aeromodelers can face
trying to get started in this hobby. These
particular problems were largely associated
with (i.e., because of) products peddled as
Almost Ready-to-Fly (ARF) “trainers” that
were anything but.
At that time I was trying hard to help some
people in this situation, and I began thinking
about all of the things I’ve seen happen with
first-timers at the stick—for more than 40
years. Having flown RC since the mid-1950s,
I did not need a basic trainer but was
motivated by observing some people who did.
This resulted in a design challenge for
me—just for the fun of it. I wondered about
ways to approach this need and set about
some design goals for a compromise
beginner’s design. The result, shown in some
photos, is “Stikum.”
Stikum is somewhat a large park flyer
conceptually, but it really needs a regular
flying field. (I have some reservations about
anyone learning to fly anything in parks; they
are generally too public, and safety is a
concern.) The Stikum’s design puts it in the
middle, between smaller park flyers and
larger wet-power trainer models that are
popular at many club fields. I feel that Stikum
can fit in a bit better in a wider range of
venues.
Stikum is patterned in part after the
Revolt! (featured in the 11/94 MA); it has the
same airfoil and a 600-square-inch wing,
although it’s more lightly and simply
structured. The same is true for the built-up
tail surfaces. The fuselage is clearly
different—inspired by some popular park
flyers.
Bob Kopski, 25 West End Dr., Lansdale PA 19446
RADIO CONTROL ELECTRICS
An overview of Stikum: a docile Electric model that is rather hard to damage. Nearly
everything “gives” a little during a mishap, minimizing breakage.
Detail of the motor mount and motor-plate attachment; two brass straps, four screws,
blind nuts in the motor plate secure the latter to the fuselage boom.
Dual 1⁄8 light plywood pylon verticals, 1⁄8 balsa saddle plates, 1⁄4 through wing dowel form
wing mount. The seven-cell pack is Velcroed underneath it all.
airplane wiring. This connector set is also the
“switch”; everything is powered when the
pack is plugged in.
To further accommodate those hard first
landings, the geared Astro 05 is mounted on a
field-replaceable 1⁄8 birch plywood “break-off
plate.” The idea is for this specific piece to
fail before any other part of the fuselage
structure does. This motor plate is firmly
clamped to the 1⁄2-inch square white pine (or
spruce) fuselage boom with screws and small
metal plates.
The motor, nested in a “V” block, is
clamped to the plate using Gold-N-Rod inners
and 2-56 machine screws. There is no glue
used in this area, so a spare plate and a
screwdriver can easily get your model back in
the air following a mishap.
Given that an 11- or 12-inch wood
propeller is usually strong and that just it
striking the ground could cause a motor-plate
failure, I chose a Master Airscrew 12 x 8
folder with the hub screws snugged a bit—so
the blades don’t flop around. Here, the
propeller is not intended (and not wanted) to
be a normal folder, but a propeller with blades
that can yield backward instead of holding
firm during a propeller strike.
The 1⁄8-inch-diameter wire landing gear
(with fairly large, light wheels) is somewhat
springy but holds up well during takeoff and
landing rolls. This assembly also tends to give
rather than bend or break free. This works
because whatever Stikum does it does
slowly—assured by the low all-up weight (49
ounces), large wing, and thick wing section
(121⁄2%). Typical liftoff from mowed grass is
20-30 feet, and not much forward speed is
needed to accomplish it.
One goal I did not reach was my design
target of 48 ounces all up. The extra ounce
can be blamed on my using my own-design
Sport Speed Control (9/99 and 10/99 MA),
which is heavier and more bulky than almost
any contemporary commercial Electronic
Speed Control (ESC). In any case, a BEC
(Battery Eliminator Circuit) saves the weight
of a radio battery—part of the original
planning.
One interesting (for me) and exciting (for
him) field experience came about when I
offered a beginner—who had only flown a
small Electric by hand launching a few
times—the opportunity to ROG Stikum. He
reluctantly, nervously tried it. His first attempt
failed because of steering fumbles, but the
model got off easily thereafter; he was
smiling ear-to-ear.
Once airborne, the beginner seemed to
find himself immediately comfortable with
Stikum; I think because this is one of those
airplanes that flies “slower than the speed of
thought.” I think he would have bought
Stikum on the spot were it available!
Contrary to what one might think, a
skilled pilot can fly Stikum in rather breezy
conditions. But then a skilled pilot would
likely not want a Stikum, right? Wrong!
What began as a design challenge for
me—a fun experiment of sorts—has yielded
an easygoing, rather lazy, land-at-your-feet
flier that has brought requests for plans from
the local flightline—a completely unexpected
outcome. The finger-pointing chuckles I
expected when I first brought Stikum out
never happened. This easy-to-build, low-cost
project has turned out to be an appealing,
docile, nice-flying E-aeromodel. Serendipity!
(That might be a better name than Stikum!)
I recognize that this design is not the best
for every early training need. No model can
be. It lies somewhere between a small, calmair-
only park flyer and a howling-hog 40 wet
machine. The Stikum concept is just another
approach—another option—perhaps
appealing to some and unappealing to others.
However, it does illustrate what can happen in
pursuit of a challenge. Maybe it will give you
some ideas of your own.
No matter how much some topics are
covered, there are always newcomers with the
same questions and/or those who know they
read something somewhere but need a
refresher. And every now and then, along
comes a never-before-asked reader question.
Following are some new and some longrunning
topics of reader inquiry.
My recent columns have waxed hard on
the chokes topic, and several readers have
come up with the same question: “Do chokes
have direction?” No! Chokes are like resistors
in this respect; you can use (connect) either of
the two leads either way. Chokes have no
“polarity.” For the sake of completeness,
106 MODEL AVIATION
some electronic components do have
direction or polarity, such as all
semiconductors (e.g., diodes) and most (but
not all) electrolytic capacitors.
Since many ask, it is impossible for me to
easily copy columns and send them to you.
This recurring request apparently comes
from my frequent references to earlier
column topics. However, you can get article
reprints from AMA Headquarters. Unless I
make a specific offer of such (e.g., Universal
Slow Charger Parts Update), please don’t put
me in the position of having to say no; I
much prefer reader letters to which I can say
yes or make some other positive reply!
Another common reader query involves
multimotor installations. Beginning with
two-motor (twin) systems, following are
some basic guidelines. Two (brushed) motors
can be wired in parallel or series. In either
case, only one speed control is generally
needed. (Extremely large power systems may
need multiple ESCs, and brushless systems
typically have separate, noninterconnected
motors/controllers.)
“Parallel” means that both positive (+)
motor terminals are wired together, and both
negative (–) motor terminals are wired
together, and that is how they are wired to
the ESC. “Series” means that the positive (+)
terminal of one motor is wired to the
negative (–) terminal of the other. Then the
negative (–) terminal of the first and the
positive (+) terminal of the second are the
108 MODEL AVIATION
final or overall motor terminal connections;
these are what the ESC drives.
Two motors wired in parallel consume
twice the current of a single motor—all
other conditions being equal. Both motors
would “see” the same applied voltage (cell
count) as either would as a single motor.
A pair of motors wired in series have the
same current flowing in each, and this
current would be the same value as if with a
single motor. However, the two-motorseries
combination requires twice the
applied voltage (cell count) as a single
motor.
In either case, for a given individual
motor power level and running duration, the
battery weight in a twin is nominally double
that of the single motor case. This is
because for parallel motors drawing twice
the current of one, cells of twice the
capacity (and nominal weight) would be
indicated. Series motors tend to suggest
twice as many of the same capacity cells as
for one motor—again, twice the battery
weight.
Other considerations involve the ESC
requirements. Parallel motors, with twice
the current demand, dictate a highercurrent-
capability ESC. Not only that, but
doubling the system current can have
implications on wire gauge, switch and fuse
ratings, and connector considerations.
My “dividing line” is somewhere
between 10 and 15 amps per motor. I’m
more inclined to use parallel wiring at the
lower end of the range (with 10-amp Speed
400s and smaller) and series wiring at and
beyond the upper end of the range—say,
with motors normally running 15 amps and
higher singly. This is my guideline for sport
flying—not a hard-and-fast capital rule for
application. Next month I’ll consider the
more-than-two-motor case.
Thus ends one more column. Please
include an SASE with any correspondence
for which you’d like a reply. Everyone so
doing does get one! And do enjoy the
refreshing delight that early springtime
Electric flying brings! MA
Edition: Model Aviation - 2003/05
Page Numbers: 104,106,108
104 MODEL AVIATION
THIS COLUMN OFFERS one meet
announcement, describes an Electric built to
meet a design challenge, and reviews a
variety of new and classic reader questions.
Colin McKinley—an E-modeler friend from
long ago—wrote to announce an Electric funfly
hosted by the Riverside Aero Modelers. It
is scheduled for August 23-24 in King, North
Carolina—near Winston-Salem. Not all of the
details are finalized as I write this, but they
will be by the time you read it.
You can get full info from Contest
Director Randy Covington at (336) 983-9126
or [email protected]. You can
also write to Colin at 4003 Poindexter Ave.,
Winston-Salem NC 27106. When you see
Colin at the meet (he’ll be the guy flying
numerous vintage Radio Control [RC] Econversions),
be sure to tell him Bob sent ya!
As described in recent columns, last summer
brought to my attention some special
difficulties would-be E-aeromodelers can face
trying to get started in this hobby. These
particular problems were largely associated
with (i.e., because of) products peddled as
Almost Ready-to-Fly (ARF) “trainers” that
were anything but.
At that time I was trying hard to help some
people in this situation, and I began thinking
about all of the things I’ve seen happen with
first-timers at the stick—for more than 40
years. Having flown RC since the mid-1950s,
I did not need a basic trainer but was
motivated by observing some people who did.
This resulted in a design challenge for
me—just for the fun of it. I wondered about
ways to approach this need and set about
some design goals for a compromise
beginner’s design. The result, shown in some
photos, is “Stikum.”
Stikum is somewhat a large park flyer
conceptually, but it really needs a regular
flying field. (I have some reservations about
anyone learning to fly anything in parks; they
are generally too public, and safety is a
concern.) The Stikum’s design puts it in the
middle, between smaller park flyers and
larger wet-power trainer models that are
popular at many club fields. I feel that Stikum
can fit in a bit better in a wider range of
venues.
Stikum is patterned in part after the
Revolt! (featured in the 11/94 MA); it has the
same airfoil and a 600-square-inch wing,
although it’s more lightly and simply
structured. The same is true for the built-up
tail surfaces. The fuselage is clearly
different—inspired by some popular park
flyers.
Bob Kopski, 25 West End Dr., Lansdale PA 19446
RADIO CONTROL ELECTRICS
An overview of Stikum: a docile Electric model that is rather hard to damage. Nearly
everything “gives” a little during a mishap, minimizing breakage.
Detail of the motor mount and motor-plate attachment; two brass straps, four screws,
blind nuts in the motor plate secure the latter to the fuselage boom.
Dual 1⁄8 light plywood pylon verticals, 1⁄8 balsa saddle plates, 1⁄4 through wing dowel form
wing mount. The seven-cell pack is Velcroed underneath it all.
airplane wiring. This connector set is also the
“switch”; everything is powered when the
pack is plugged in.
To further accommodate those hard first
landings, the geared Astro 05 is mounted on a
field-replaceable 1⁄8 birch plywood “break-off
plate.” The idea is for this specific piece to
fail before any other part of the fuselage
structure does. This motor plate is firmly
clamped to the 1⁄2-inch square white pine (or
spruce) fuselage boom with screws and small
metal plates.
The motor, nested in a “V” block, is
clamped to the plate using Gold-N-Rod inners
and 2-56 machine screws. There is no glue
used in this area, so a spare plate and a
screwdriver can easily get your model back in
the air following a mishap.
Given that an 11- or 12-inch wood
propeller is usually strong and that just it
striking the ground could cause a motor-plate
failure, I chose a Master Airscrew 12 x 8
folder with the hub screws snugged a bit—so
the blades don’t flop around. Here, the
propeller is not intended (and not wanted) to
be a normal folder, but a propeller with blades
that can yield backward instead of holding
firm during a propeller strike.
The 1⁄8-inch-diameter wire landing gear
(with fairly large, light wheels) is somewhat
springy but holds up well during takeoff and
landing rolls. This assembly also tends to give
rather than bend or break free. This works
because whatever Stikum does it does
slowly—assured by the low all-up weight (49
ounces), large wing, and thick wing section
(121⁄2%). Typical liftoff from mowed grass is
20-30 feet, and not much forward speed is
needed to accomplish it.
One goal I did not reach was my design
target of 48 ounces all up. The extra ounce
can be blamed on my using my own-design
Sport Speed Control (9/99 and 10/99 MA),
which is heavier and more bulky than almost
any contemporary commercial Electronic
Speed Control (ESC). In any case, a BEC
(Battery Eliminator Circuit) saves the weight
of a radio battery—part of the original
planning.
One interesting (for me) and exciting (for
him) field experience came about when I
offered a beginner—who had only flown a
small Electric by hand launching a few
times—the opportunity to ROG Stikum. He
reluctantly, nervously tried it. His first attempt
failed because of steering fumbles, but the
model got off easily thereafter; he was
smiling ear-to-ear.
Once airborne, the beginner seemed to
find himself immediately comfortable with
Stikum; I think because this is one of those
airplanes that flies “slower than the speed of
thought.” I think he would have bought
Stikum on the spot were it available!
Contrary to what one might think, a
skilled pilot can fly Stikum in rather breezy
conditions. But then a skilled pilot would
likely not want a Stikum, right? Wrong!
What began as a design challenge for
me—a fun experiment of sorts—has yielded
an easygoing, rather lazy, land-at-your-feet
flier that has brought requests for plans from
the local flightline—a completely unexpected
outcome. The finger-pointing chuckles I
expected when I first brought Stikum out
never happened. This easy-to-build, low-cost
project has turned out to be an appealing,
docile, nice-flying E-aeromodel. Serendipity!
(That might be a better name than Stikum!)
I recognize that this design is not the best
for every early training need. No model can
be. It lies somewhere between a small, calmair-
only park flyer and a howling-hog 40 wet
machine. The Stikum concept is just another
approach—another option—perhaps
appealing to some and unappealing to others.
However, it does illustrate what can happen in
pursuit of a challenge. Maybe it will give you
some ideas of your own.
No matter how much some topics are
covered, there are always newcomers with the
same questions and/or those who know they
read something somewhere but need a
refresher. And every now and then, along
comes a never-before-asked reader question.
Following are some new and some longrunning
topics of reader inquiry.
My recent columns have waxed hard on
the chokes topic, and several readers have
come up with the same question: “Do chokes
have direction?” No! Chokes are like resistors
in this respect; you can use (connect) either of
the two leads either way. Chokes have no
“polarity.” For the sake of completeness,
106 MODEL AVIATION
some electronic components do have
direction or polarity, such as all
semiconductors (e.g., diodes) and most (but
not all) electrolytic capacitors.
Since many ask, it is impossible for me to
easily copy columns and send them to you.
This recurring request apparently comes
from my frequent references to earlier
column topics. However, you can get article
reprints from AMA Headquarters. Unless I
make a specific offer of such (e.g., Universal
Slow Charger Parts Update), please don’t put
me in the position of having to say no; I
much prefer reader letters to which I can say
yes or make some other positive reply!
Another common reader query involves
multimotor installations. Beginning with
two-motor (twin) systems, following are
some basic guidelines. Two (brushed) motors
can be wired in parallel or series. In either
case, only one speed control is generally
needed. (Extremely large power systems may
need multiple ESCs, and brushless systems
typically have separate, noninterconnected
motors/controllers.)
“Parallel” means that both positive (+)
motor terminals are wired together, and both
negative (–) motor terminals are wired
together, and that is how they are wired to
the ESC. “Series” means that the positive (+)
terminal of one motor is wired to the
negative (–) terminal of the other. Then the
negative (–) terminal of the first and the
positive (+) terminal of the second are the
108 MODEL AVIATION
final or overall motor terminal connections;
these are what the ESC drives.
Two motors wired in parallel consume
twice the current of a single motor—all
other conditions being equal. Both motors
would “see” the same applied voltage (cell
count) as either would as a single motor.
A pair of motors wired in series have the
same current flowing in each, and this
current would be the same value as if with a
single motor. However, the two-motorseries
combination requires twice the
applied voltage (cell count) as a single
motor.
In either case, for a given individual
motor power level and running duration, the
battery weight in a twin is nominally double
that of the single motor case. This is
because for parallel motors drawing twice
the current of one, cells of twice the
capacity (and nominal weight) would be
indicated. Series motors tend to suggest
twice as many of the same capacity cells as
for one motor—again, twice the battery
weight.
Other considerations involve the ESC
requirements. Parallel motors, with twice
the current demand, dictate a highercurrent-
capability ESC. Not only that, but
doubling the system current can have
implications on wire gauge, switch and fuse
ratings, and connector considerations.
My “dividing line” is somewhere
between 10 and 15 amps per motor. I’m
more inclined to use parallel wiring at the
lower end of the range (with 10-amp Speed
400s and smaller) and series wiring at and
beyond the upper end of the range—say,
with motors normally running 15 amps and
higher singly. This is my guideline for sport
flying—not a hard-and-fast capital rule for
application. Next month I’ll consider the
more-than-two-motor case.
Thus ends one more column. Please
include an SASE with any correspondence
for which you’d like a reply. Everyone so
doing does get one! And do enjoy the
refreshing delight that early springtime
Electric flying brings! MA
