114 MODEL AVIATION
THIS COLUMN COMMENTS on
Dump’r, suggests a needed E-product, leaps
from “too little” to “too much,” and
continues the discussion of basic electrical
terms and concepts.
You did it! You made it happen! Never has
there been a faster, larger reader reaction
than in recent months regarding Dump’r.
This versatile battery discharger offered as a
test topic in the June column is a feature in
this issue.
Your immediate and continuing flood of
requests to publish Dump’r caused me to
quickly compile all of the necessary
information and offer it to Model Aviation
for consideration. As a result, Dump’r is
included herein for your consideration and
construction. Thank you for your interest
and vote of confidence in Dump’r.
Included in the many letters were
numerous repeat questions—and
misconceptions. Dump’r as designed and
presented is for Ni-Cd and NiMH packs of
four to 18 cells. It has a fixed discharge
current, and, no, it cannot safely be
increased! But it could be reduced.
Dump’r itself does not “cycle” packs—
that’s not its purpose—and it can’t charge!
Dump’r does not measure or record the
discharge parameters, although because of
its fixed discharge current, you could time
its operation and deduce the information—
but that would be very boring.
That covers most reader queries and
comments about Dump’r. However, since so
many readers inquired about measuring the
battery’s discharge (capacity), I have
reviewed the possibility. I can imagine a
simple “add-on” to allow this.
Initially, at least, I see a possible way to
automatically, inexpensively get the “time”
parameter, but this needs to be developed
and tested. If it works out, I’ll offer it as a
simple supplement to Dump’r in a future
column.
In the meantime, I’m confident that you
will find Dump’r to be everything it’s
described to be and that you will be quite
happy with its intended operation. I have
four of them!
The potential add-on—as I imagine it
now—will not significantly alter Dump’r as
presented. Please don’t delay in building
Dump’r because of this uncertain addition. If
and when I can offer the extra timing utility,
it will likely only require a small additional
connector on the box; otherwise, I wouldn’t
consider it “simple.” Besides, I don’t want to
mess up my own Dump’rs!
And please don’t request early info. I’m
uncomfortable sharing design on the fly; I
much prefer to share finished, documented,
proven stuff.
Despite the vastness of present-day electric
technology and market offerings, there is
one E-product missing. Most modelers know
and appreciate the convenience of the
Battery Eliminator Circuit (BEC) feature
that is part of many Electronic Speed
Controls (ESCs). A BEC allows one to
power the radio system with regulated
voltage derived from the motor battery; that
is, BEC is a receiver-battery substitute, or
alternative.
This has the clear benefit that you do not
have to install and maintain the classic radio
pack, as do our wet-power-flying friends.
However, the current BEC does have its
limitations; the main one is that it can only
be used in “smaller” installations.
Generally the BECs I’ve seen are limited
in the number of cells allowed in the motor
pack and the number of servos allowed in
the system. This is a technical limitation
associated with the power-handling
capability of ordinary BEC circuitry. Thus,
one may find a BEC description of “6 to 10
cells” and “2 to 3 servos.” (The specifics
vary with the product.)
The reason for these limitations is that all
ESC BECs I know of incorporate linear
regulators. Linear regulators are inefficient
and normally get rather warm to fairly hot,
and this natural temperature rise must be
held to safe operational levels. That is done
by limiting cell and/or servo counts.
I’d like to see the ESC/BEC idea
implemented in efficient switch-mode
circuitry rather than inefficient linear
circuitry. This would eliminate heat-related
concerns and could dramatically raise
permissible cell and servo counts.
But switch-mode circuitry needs more
electronic stuff to implement, so this would
probably increase a given ESC’s physical
size and weight. It would also be more
costly. However, the size and weight growth
would be much less than the volume and
weight of the classic radio pack, and it might
even be a toss-up with respect to cost.
Furthermore, as with BECs now, it would
minimize wiring in the model and totally
eliminate the receiver-pack charging and
other maintenance. Such a BEC
implementation would allow large Electrics
to be every bit as convenient as small
Electrics can be now; i.e., those that benefit
from limited but useful present-day BECs.
Who will be the first ESC manufacturer
to get onboard with this product wish?
The vastness of today’s electric technology
and product array brings to my mind the
earliest days of silent power—not because of
the similarity, but because of the difference!
Or is it?
Having “been there,” beginning in the
early 1970s—with nearly no E-product and
no E-interest to be found—I can greatly
appreciate the huge difference three decades
have made. What a large and glorious
change! It’s terrific, right?
Not for everyone. For some, E-power
still offers a challenge: the paradoxical
challenge of too much choice.
In the earlier years of this column, I
frequently addressed the common reader cry
of “which motor, which model?” Nowadays
it’s more like “which motor”—because the
model no longer matters as much. Now one
has many choices of E-quipment for almost
any airplane.
More and more I’m experiencing the
frustrated reader who has difficulty choosing
between one product and others that are
similar; there are so many that seem so much
alike. It’s like pulling into an empty parking
lot and having to decide in which space to
park.
Consider the contemporary motor
marketplace. A look through paper or
electronic catalogs for suppliers such as
Hobby Lobby, Northeast Sailplane Products,
New Creations R/C, and many more
illustrates a veritable blizzard of model
motors, and many seem eligible for the same
application. How does one choose? What’s
more, this quandary is not limited to motors;
it includes most other E-stuff.
One approach to this “new” problem is
the same as for the “old” one, because it’s
really ongoing. The trick is to look for
examples. The July column described the
numerous E-info resources presently
available to everyone. Included therein is an
abundance of accomplishments by others
that can become guidelines for you.
No matter your choice of E-project, you
are highly likely to find something similar in
Bob Kopski, 25 West End Dr., Lansdale PA 19446
RADIO CONTROL ELECTRICS
For some, E-power still
offers a challenge:
the paradoxical challenge
of too much choice.
the references, and from them you can more
easily and more confidently choose a
satisfactory power-system makeup; copy
what was successful for someone else.
Those same resources can suggest
choices besides the motor; e.g., for speed
controls, battery makeup, and even
propellers. I ask again as I did in the July
column: How do you think electric power
got from so little to so much through the
decades? The answer: More and more Emodelers
making/sharing more and more Eaccomplishments
in the course of time.
The last two columns discussed common
electrical terms such as voltage and current
and illustrated how to use multimeters to
measure these quantities. This knowledge
can help you not only troubleshoot, but also
optimize your E-power system.
And although getting into this detail is
not a requirement to enjoy electric, having
such knowledge and ability can add much to
the enjoyment of E-power for those who are
so inclined. It’s a little like enjoying a
sports-car ride through the countryside or
doing the same thing knowing that you finetuned
your own car.
Previously you learned that voltmeters
are always connected across terminals—
such as battery or motor terminals. Also,
current (amp) meters are always connected
in series in a closed circuit.
You learned that good voltmeters are
high-resistance devices that minimally
disturb what they are measuring.
Furthermore, and similarly, good ammeters
are low-resistance devices that “use up” little
of the available circuit voltage. One graphic
summarizes all this.
Now to complicate things a bit. Or
maybe this is actually a simplification! It
depends on how you see it.
In electric, because power systems
normally have “high” currents present in a
compactly assembled installation confined to
a small space, one does not normally directly
use the ammeter part of a multimeter to
measure these currents. This is because of
practicalities—not the principles involved.
For one thing, most Digital Multimeter
(DMM) ammeter functions are limited to 10
or 20 amps maximum, and this is inadequate
for higher-power E-systems. Furthermore,
just connecting to such a DMM requires test
leads that are much different from those
commonly supplied. Those 3- or 4-foot,
light-gauge wires and probes that come with
a typical DMM are not so good with 20
amps flowing!
That is because this test-lead wire is
added to a circuit that normally has short,
heavy wiring within itself, and the additional
length and associated electrical loss of light
wire can significantly alter power-system
behavior. Such measurement could alter
what is being measured.
Using a typical DMM’s ammeter
function directly in an E-power system
requires some custom, short, heavy, properly
connected test leads. Although this is not a
serious challenge, it does physically locate
the instrument close to the “stuff” in the
model—and the propeller—which is a less
than best situation. What to do?
This brings me to the more fundamental
question of how the ammeter works. In the
case of DMMs, the ammeter function is
really the internal voltmeter (i.e., the DVM
part) reading the voltage on a built-in shunt
(sampling) resistor.
That is, when you use the DMM’s
ammeter option, you are actually routing
circuit current through a sampling resistor
internal to the instrument, and the internal
voltage metering is reading the voltage that
appears on that resistor. (Remember that
voltmeters measure across terminals.) While
it’s a sampled voltage being measured, the
instrument display reads out in amps.
(If you are unsure at this point, appreciate
that when current is flowing through a
resistor, a resulting voltage appears across
that resistor. This is exactly the same thing—
though viewed differently—as current
flowing through a resistor when voltage is
impressed on it. I’ll expand on this subtlety
later in this miniseries.)
Expanding on this idea, but
implementing it vastly better for our “highcurrent”
application, one can insert a
separate or external shunt (sampling resistor)
in an existing motor circuit—say at a
connector set—then use a DVM to read
voltage appearing on this shunt when motor
current flows.
Hence in this application, a shunt
samples current and displays the current
magnitude in terms of voltage that can be
read “at a distance” since the lead length to
the instrument does not affect a voltage
reading.
A shunt is characterized with a
descriptive constant (usually) expressed as
millivolts per amp; a typical shunt constant
might be 1mV/Amp. This means that for
each amp that passes through this shunt, one
millivolt will appear; that is because this
shunt is a precise 1-milliohm (1⁄1000 ohm)
resistor that is capable of safely carrying
“high” current.
Such a shunt, situated “locally” or in situ,
introduces minimal resistance and voltage
loss within the circuit being measured. A
good shunt—one with short interconnects
and a suitable low mV/Amp constant—
imposes minimal burden on the circuit under
test. Therefore, in our application a motorcircuit
installation would be minimally
impacted by the presence of the shunt.
For those with an MA library at hand, this
idea was detailed in the January 1993
column. I’ll discuss it more next month.
Later in this continuing miniseries we’ll see
how one dedicated product—the AstroFlight
Whattmeter—does all of the preceding and
much more in a simple and convenient way.
Thus ends one more column. Please enclose
an SASE with any correspondence for which
you’d like a reply. Everyone so doing does
get one!
Happy and numerous safe E-landings,
everyone! MA
October 2003 115
OVER 100 LITHIUM-ION
BATTERY PACKS TO
CHOOSE FROM
MULTI-VOLTAGE MODULES
POWER REGULATORS
CHARGERS
CLIP-ON-COCKPIT
TELEMETRY SYSTEM
R/C Power Solutions
“...Great Products...
Great Customer Service...”
2002 TOC CHAMPION
CHIP HYDE
FROM MICRO-FLYERS...
...TO GIANT SCALE...
...LAND, SEA AND AIR...
WE HAVE A POWER SYSTEM
THAT’S “LITE” FOR YOU!
Contact:
Skyborn Electronics
3405 Express Dr.
Garland, TX 75041
972-267-5099 Fax: 972-271-3529
www.rcpowerflite.com
[email protected]
ULTRA BRITE LITES
NEW
NEED
MORE
INFO?
See your hobby retailer or send a #10 S.A.S.E. to
229 E. Rollins Rd. Round Lake Beach, IL 60073
847-740-8726 Fax 847-740-8727
www.RamRCandRamTrack.com
Edition: Model Aviation - 2003/10
Page Numbers: 114,115
Edition: Model Aviation - 2003/10
Page Numbers: 114,115
114 MODEL AVIATION
THIS COLUMN COMMENTS on
Dump’r, suggests a needed E-product, leaps
from “too little” to “too much,” and
continues the discussion of basic electrical
terms and concepts.
You did it! You made it happen! Never has
there been a faster, larger reader reaction
than in recent months regarding Dump’r.
This versatile battery discharger offered as a
test topic in the June column is a feature in
this issue.
Your immediate and continuing flood of
requests to publish Dump’r caused me to
quickly compile all of the necessary
information and offer it to Model Aviation
for consideration. As a result, Dump’r is
included herein for your consideration and
construction. Thank you for your interest
and vote of confidence in Dump’r.
Included in the many letters were
numerous repeat questions—and
misconceptions. Dump’r as designed and
presented is for Ni-Cd and NiMH packs of
four to 18 cells. It has a fixed discharge
current, and, no, it cannot safely be
increased! But it could be reduced.
Dump’r itself does not “cycle” packs—
that’s not its purpose—and it can’t charge!
Dump’r does not measure or record the
discharge parameters, although because of
its fixed discharge current, you could time
its operation and deduce the information—
but that would be very boring.
That covers most reader queries and
comments about Dump’r. However, since so
many readers inquired about measuring the
battery’s discharge (capacity), I have
reviewed the possibility. I can imagine a
simple “add-on” to allow this.
Initially, at least, I see a possible way to
automatically, inexpensively get the “time”
parameter, but this needs to be developed
and tested. If it works out, I’ll offer it as a
simple supplement to Dump’r in a future
column.
In the meantime, I’m confident that you
will find Dump’r to be everything it’s
described to be and that you will be quite
happy with its intended operation. I have
four of them!
The potential add-on—as I imagine it
now—will not significantly alter Dump’r as
presented. Please don’t delay in building
Dump’r because of this uncertain addition. If
and when I can offer the extra timing utility,
it will likely only require a small additional
connector on the box; otherwise, I wouldn’t
consider it “simple.” Besides, I don’t want to
mess up my own Dump’rs!
And please don’t request early info. I’m
uncomfortable sharing design on the fly; I
much prefer to share finished, documented,
proven stuff.
Despite the vastness of present-day electric
technology and market offerings, there is
one E-product missing. Most modelers know
and appreciate the convenience of the
Battery Eliminator Circuit (BEC) feature
that is part of many Electronic Speed
Controls (ESCs). A BEC allows one to
power the radio system with regulated
voltage derived from the motor battery; that
is, BEC is a receiver-battery substitute, or
alternative.
This has the clear benefit that you do not
have to install and maintain the classic radio
pack, as do our wet-power-flying friends.
However, the current BEC does have its
limitations; the main one is that it can only
be used in “smaller” installations.
Generally the BECs I’ve seen are limited
in the number of cells allowed in the motor
pack and the number of servos allowed in
the system. This is a technical limitation
associated with the power-handling
capability of ordinary BEC circuitry. Thus,
one may find a BEC description of “6 to 10
cells” and “2 to 3 servos.” (The specifics
vary with the product.)
The reason for these limitations is that all
ESC BECs I know of incorporate linear
regulators. Linear regulators are inefficient
and normally get rather warm to fairly hot,
and this natural temperature rise must be
held to safe operational levels. That is done
by limiting cell and/or servo counts.
I’d like to see the ESC/BEC idea
implemented in efficient switch-mode
circuitry rather than inefficient linear
circuitry. This would eliminate heat-related
concerns and could dramatically raise
permissible cell and servo counts.
But switch-mode circuitry needs more
electronic stuff to implement, so this would
probably increase a given ESC’s physical
size and weight. It would also be more
costly. However, the size and weight growth
would be much less than the volume and
weight of the classic radio pack, and it might
even be a toss-up with respect to cost.
Furthermore, as with BECs now, it would
minimize wiring in the model and totally
eliminate the receiver-pack charging and
other maintenance. Such a BEC
implementation would allow large Electrics
to be every bit as convenient as small
Electrics can be now; i.e., those that benefit
from limited but useful present-day BECs.
Who will be the first ESC manufacturer
to get onboard with this product wish?
The vastness of today’s electric technology
and product array brings to my mind the
earliest days of silent power—not because of
the similarity, but because of the difference!
Or is it?
Having “been there,” beginning in the
early 1970s—with nearly no E-product and
no E-interest to be found—I can greatly
appreciate the huge difference three decades
have made. What a large and glorious
change! It’s terrific, right?
Not for everyone. For some, E-power
still offers a challenge: the paradoxical
challenge of too much choice.
In the earlier years of this column, I
frequently addressed the common reader cry
of “which motor, which model?” Nowadays
it’s more like “which motor”—because the
model no longer matters as much. Now one
has many choices of E-quipment for almost
any airplane.
More and more I’m experiencing the
frustrated reader who has difficulty choosing
between one product and others that are
similar; there are so many that seem so much
alike. It’s like pulling into an empty parking
lot and having to decide in which space to
park.
Consider the contemporary motor
marketplace. A look through paper or
electronic catalogs for suppliers such as
Hobby Lobby, Northeast Sailplane Products,
New Creations R/C, and many more
illustrates a veritable blizzard of model
motors, and many seem eligible for the same
application. How does one choose? What’s
more, this quandary is not limited to motors;
it includes most other E-stuff.
One approach to this “new” problem is
the same as for the “old” one, because it’s
really ongoing. The trick is to look for
examples. The July column described the
numerous E-info resources presently
available to everyone. Included therein is an
abundance of accomplishments by others
that can become guidelines for you.
No matter your choice of E-project, you
are highly likely to find something similar in
Bob Kopski, 25 West End Dr., Lansdale PA 19446
RADIO CONTROL ELECTRICS
For some, E-power still
offers a challenge:
the paradoxical challenge
of too much choice.
the references, and from them you can more
easily and more confidently choose a
satisfactory power-system makeup; copy
what was successful for someone else.
Those same resources can suggest
choices besides the motor; e.g., for speed
controls, battery makeup, and even
propellers. I ask again as I did in the July
column: How do you think electric power
got from so little to so much through the
decades? The answer: More and more Emodelers
making/sharing more and more Eaccomplishments
in the course of time.
The last two columns discussed common
electrical terms such as voltage and current
and illustrated how to use multimeters to
measure these quantities. This knowledge
can help you not only troubleshoot, but also
optimize your E-power system.
And although getting into this detail is
not a requirement to enjoy electric, having
such knowledge and ability can add much to
the enjoyment of E-power for those who are
so inclined. It’s a little like enjoying a
sports-car ride through the countryside or
doing the same thing knowing that you finetuned
your own car.
Previously you learned that voltmeters
are always connected across terminals—
such as battery or motor terminals. Also,
current (amp) meters are always connected
in series in a closed circuit.
You learned that good voltmeters are
high-resistance devices that minimally
disturb what they are measuring.
Furthermore, and similarly, good ammeters
are low-resistance devices that “use up” little
of the available circuit voltage. One graphic
summarizes all this.
Now to complicate things a bit. Or
maybe this is actually a simplification! It
depends on how you see it.
In electric, because power systems
normally have “high” currents present in a
compactly assembled installation confined to
a small space, one does not normally directly
use the ammeter part of a multimeter to
measure these currents. This is because of
practicalities—not the principles involved.
For one thing, most Digital Multimeter
(DMM) ammeter functions are limited to 10
or 20 amps maximum, and this is inadequate
for higher-power E-systems. Furthermore,
just connecting to such a DMM requires test
leads that are much different from those
commonly supplied. Those 3- or 4-foot,
light-gauge wires and probes that come with
a typical DMM are not so good with 20
amps flowing!
That is because this test-lead wire is
added to a circuit that normally has short,
heavy wiring within itself, and the additional
length and associated electrical loss of light
wire can significantly alter power-system
behavior. Such measurement could alter
what is being measured.
Using a typical DMM’s ammeter
function directly in an E-power system
requires some custom, short, heavy, properly
connected test leads. Although this is not a
serious challenge, it does physically locate
the instrument close to the “stuff” in the
model—and the propeller—which is a less
than best situation. What to do?
This brings me to the more fundamental
question of how the ammeter works. In the
case of DMMs, the ammeter function is
really the internal voltmeter (i.e., the DVM
part) reading the voltage on a built-in shunt
(sampling) resistor.
That is, when you use the DMM’s
ammeter option, you are actually routing
circuit current through a sampling resistor
internal to the instrument, and the internal
voltage metering is reading the voltage that
appears on that resistor. (Remember that
voltmeters measure across terminals.) While
it’s a sampled voltage being measured, the
instrument display reads out in amps.
(If you are unsure at this point, appreciate
that when current is flowing through a
resistor, a resulting voltage appears across
that resistor. This is exactly the same thing—
though viewed differently—as current
flowing through a resistor when voltage is
impressed on it. I’ll expand on this subtlety
later in this miniseries.)
Expanding on this idea, but
implementing it vastly better for our “highcurrent”
application, one can insert a
separate or external shunt (sampling resistor)
in an existing motor circuit—say at a
connector set—then use a DVM to read
voltage appearing on this shunt when motor
current flows.
Hence in this application, a shunt
samples current and displays the current
magnitude in terms of voltage that can be
read “at a distance” since the lead length to
the instrument does not affect a voltage
reading.
A shunt is characterized with a
descriptive constant (usually) expressed as
millivolts per amp; a typical shunt constant
might be 1mV/Amp. This means that for
each amp that passes through this shunt, one
millivolt will appear; that is because this
shunt is a precise 1-milliohm (1⁄1000 ohm)
resistor that is capable of safely carrying
“high” current.
Such a shunt, situated “locally” or in situ,
introduces minimal resistance and voltage
loss within the circuit being measured. A
good shunt—one with short interconnects
and a suitable low mV/Amp constant—
imposes minimal burden on the circuit under
test. Therefore, in our application a motorcircuit
installation would be minimally
impacted by the presence of the shunt.
For those with an MA library at hand, this
idea was detailed in the January 1993
column. I’ll discuss it more next month.
Later in this continuing miniseries we’ll see
how one dedicated product—the AstroFlight
Whattmeter—does all of the preceding and
much more in a simple and convenient way.
Thus ends one more column. Please enclose
an SASE with any correspondence for which
you’d like a reply. Everyone so doing does
get one!
Happy and numerous safe E-landings,
everyone! MA
October 2003 115
OVER 100 LITHIUM-ION
BATTERY PACKS TO
CHOOSE FROM
MULTI-VOLTAGE MODULES
POWER REGULATORS
CHARGERS
CLIP-ON-COCKPIT
TELEMETRY SYSTEM
R/C Power Solutions
“...Great Products...
Great Customer Service...”
2002 TOC CHAMPION
CHIP HYDE
FROM MICRO-FLYERS...
...TO GIANT SCALE...
...LAND, SEA AND AIR...
WE HAVE A POWER SYSTEM
THAT’S “LITE” FOR YOU!
Contact:
Skyborn Electronics
3405 Express Dr.
Garland, TX 75041
972-267-5099 Fax: 972-271-3529
www.rcpowerflite.com
[email protected]
ULTRA BRITE LITES
NEW
NEED
MORE
INFO?
See your hobby retailer or send a #10 S.A.S.E. to
229 E. Rollins Rd. Round Lake Beach, IL 60073
847-740-8726 Fax 847-740-8727
www.RamRCandRamTrack.com