March 2004 125
THIS COLUMN INCLUDES follow-up
on two airplanes discussed in the January
column, adds a third, and discusses more
reader experience with Dump’r, including
the related use of ohmmeters for checkout as
part of the continuing “electrical terms and
concepts” miniseries.
I showed and wrote about the Skyvolt and
Ruckus designs with new AstroFlight
brushless power systems in the January
column. I recently retrofitted my original
Skyvolt, which was published as a
cover/feature in the January 1990 Model
Aviation, with a geared Astro two-turn
brushless 05 motor on eight cells. The
January 2004 column described the huge
difference this up-to-date power system
made; I made a whole new airplane out of
this aging original design.
I described Ruckus as a new original
aerobatic design with a geared Astro threeturn
brushless 05 motor on 10 cells. I’m
having a great time with this airplane, and
now I have four interchangeable packs with
which to fly it. I’ve been tracking Ruckus’s
flight experience for the two months of its
existence, and as of this writing I have
logged 82 flights. One graphic depicts this.
The 10-cell packs include one CP 1.7,
one “old” 2.0, one new 2.4, and one new
matched GP 3.3. The first three packs are
Ni-Cd, and the last is NiMH. Ruckus weighs
less than 51 ounces with the 1.7s and 56-57
ounces with the other three packs.
A typical flight is a continuous mix of
show-off vertical, many consecutive inside
and outside loops, rolls, 8s of all kinds,
knife edge, etc.—all of the normal stuff. All
flights include throttle management
throughout. If you add the averages shown
on the graphic, you’ll see that going to the
field with four charged packs allows me
more than 40 nearly continuous minutes of
air time, by which time I’m tired!
Having been so impressed with these two
Astro motors, I purchased a third—my
second three-turn—and retrofitted it into an
old Revolt! (which was featured in the
November 1994 MA).
The Revolt! is a docile, flat-bottom,
cabin-type model that was originally
designed to accommodate E-experiments
including power-system flight-testing,
telemetry stuff, glitch recorders, etc. Many
readers installed cameras in it. (Revolt! is
extremely versatile.)
This particular Revolt! had a geared
Cobalt 15 on 12 cells and weighed 68.5
ounces. That number dropped to 60.5
ounces with the new motor on 10 cells. As
with the Skyvolt, Revolt! power went way
up and flight duration increased.
The power increase was so dramatic that
brief vertical performance, sustained
inverted flight, and even a (large) outside
loop became possible—despite the flat
section. That’s all because of the enormous
thrust increase combined with the reduced
weight. Another dramatic manifestation was
that I could not touch the sizzling-hot 15
upon landing, but the brushless 05 is barely
warm.
These geared Astro 05 brushless motors
weigh 5.5 ounces and seem comfortable at
upward of 350 watts. My trusty, muchflown,
and much-liked 15 Cobalt is now
paperweight material! And, no, the 15 and
05 nomenclature does not mean anything
Bob Kopski, 25 West End Dr., Lansdale PA 19446
RADIO CONTROL ELECTRICS
Geared (3.3:1) AstroFlight brushless, sensorless 05 motor with older controller. Motor
and newer controller weigh only 7.5 ounces but provide heavy performance!
This provides a closer look at the nifty Astro brushless connector set. Rotating the
connector matchup by 180° changes the motor direction.
126 MODEL AVIATION
useful that I can discern, so don’t even ask!
To complete this story, I’m using a 10 x
5E propeller with the eight-cell/two-turn
system and a 12 x 6E with the 10-cell/threeturn.
My motors have the helical gearbox
option—the classic, robust Astro product
design that holds up well.
All of my installations use Castle
Creations’ Phoenix brushless, sensorless
controls—the 45 or the 60—with BEC
(Battery Eliminator Circuit). These
controllers are programmable for many
operational parameters.
I like using the “soft” cutoff option and
the correct cutoff voltage settings for the
associated cell count. The latter precludes
packs from overdischarge, which is good for
all batteries but critical with Lithium-
Polymer. As I did with the Astro motors, I
expect to buy more Castle controllers soon.
I appreciate that much of this info may
be old news to some readers, but I’m also
sensitive to the fact that many others have
not experienced or even witnessed this sort
of thing. Since I’m about to buy my fourth
geared Astro 05 brushless, it should be
obvious that I wholeheartedly recommend
this product—certainly for the range of
models I’ve described so far, but for others
too, I’m sure.
The Dump’r (featured in the October 2003
MA) continues to bring in a great deal of
reader reaction. By now there must be a
zillion Dump’rs out there! In fact, I’ve heard
that the recommended parts supplier
(Mouser) temporarily sold out of some
parts!
By now it should also be well known that
although the Dump’r design is solid and
works as described, the original article had
some writing mistakes. These were
discussed in the “Letters to the Editor”
section of the December 2003 MA, and I can
supply the details to anyone in need.
Some readers sent me problematic
Dump’rs to troubleshoot. All six I’ve
received suffered from reader-assembly
error, and all worked perfectly when they
were fixed. I discussed some reader
problems in the February 2004 column, and
following are some new ones.
The specified RadioShack PC holeboard,
a portion of which is used in Dump’r, has an
array of “horizontal” busses and two
“vertical” or edge busses. These vertical
stripes alternately connect to the more
numerous horizontal stripes. Interspersed
with this orthagonal buss array are many
isolated three-hole PC lands. (This is easier
to see than to describe.)
Two readers cut out the required board
piece in a way that they unknowingly
included residue of one of the vertical
conductors. This partially cut stripe—still
marginally connected to alternating
horizontal busses—shorted out large
amounts of the Dump’r circuit board. The
fix is easy. Scrape away the offending buss
residue with a #11 X-Acto blade. The
readers’ Dump’rs worked perfectly as soon
as I did this.
Another reader mistakenly wired the
light-emitting diode (LED) backward.
Remember that LEDs have polarity; the
cathode (negative) lead is identified by a
noticeable flat spot on the otherwise round
base.
One reader’s problem was that the fullsize
box layout/drill template drawing in MA
was inaccurate when he copied it. Be sure to
check your copier to make sure it is set to
“full size” or “100%” scale, and then
compare the copy with the original page in
MA to verify dimensional accuracy before
you drill any holes!
Another reader attempted to clear spaces
between PC-board lands with a Dremel tool
and a cutoff wheel. The abrasive wheel
smeared solder between lands and produced
much solder dust. This resulted in massive
board shorts—the very thing he tried to
eliminate! If you need to clear some land-toland
bridges, use a #11 X-Acto, a solvent
(e.g., acetone), and a brush to clean the
board bottom, and inspect all work with a
lens.
Several readers experienced problems
with Dump’r checkout following assembly.
As I do with all of my electronics feature
articles, I included information about
checking out the completed assembly with
an ohmmeter before powering it up.
This seemingly simple step generally
works fine, but a few readers experienced
incorrect readings on otherwise good
Dump’rs. This is a good transition topic into
the miniseries about electrical terms and
concepts that I began several columns ago.
The miniseries discussion in the October
2003 issue was to have an associated
graphic depicting current and voltage
measurements and the use of shunts. That
graphic missed that issue and was presented
in the December issue on page 158. You
need the October column text and the
December graphic to make them both right.
In previous columns I have discussed the
voltmeter and ammeter functions within
digital multimeters (DMMs). Let’s look at
the ohmmeter function. Its purpose is to
measure resistance, and the unit of
resistance is ohms. One ohm is the
resistance value such that if 1 volt were
applied to it, 1 amp would flow.
Ohmmeters are useful primarily in
measuring fixed resistors and can generally
produce accurate readings from low values
(a few ohms) to many millions of ohms
(megohms). This is usually accomplished
with several meter ranges (full scale values).
Typical meter ranges include 200 ohms,
2,000 ohms, 20,000 ohms (20K ohms),
200K ohms, 2 million ohms (2 megohms),
and 20 megohms, but some DMMs have
ranges based on 3s and 4s. Also, some
meters may include extended ranges such as
a 10s scale and/or higher megohm scales.
Resistors are linear devices. For instance,
if in the preceding definition 10 volts were
applied to that 1-ohm resistor, 10 amps
would flow. Thus the current that flows in
any resistor is linearly related to the applied
voltage. So at least within their published
rating limits, resistor values in ohms are
fixed and do not change with the voltage
applied.
Alternately, if a current were
independently made to flow through a
resistor, the resulting voltage appearing on
that resistor would be the current multiplied
by the resistor value. If 1⁄10 amp (100
milliamperes) were forced to flow through a
1-ohm resistor, 1⁄10 volt (100 millivolts)
would appear across it. A 1⁄100-amp (10
milliampere) current would cause 1⁄100 volt
(10 millivolts) to appear on that same 1-ohm
resistor, and a 10-ohm resistor in its place
would yield 10/100 = 1⁄10 volt.
Most digital ohmmeters work using the
latter operational methodology. DMM
ohmmeters work by electronically causing
some fixed current flow through the
unknown resistor and then measuring
(reporting) the resulting voltage disguised as
ohms.
Assume that some ohmmeter set to the
200-ohm scale applies a test current of 1
milliamp to a resistor being measured. If it
happened to be a 100-ohm resistor, 100
millivolts would appear across it. The meter
is designed to translate and display this as
100 ohms.
If the meter range were changed—say to
2K ohms—the meter might apply a reduced
test current of 1⁄10 milliampere. This would
reduce the voltage on the resistor to just 10
millivolts, but the displayed result would still
be the same nominal 100 ohms. However,
the result would be displayed with reduced
resolution (fewer significant figures) like the
example depicted in the September column
for voltage measurements.
Consider applying an ohmmeter as a
circuit-checkout device. A typical electronic
circuit (such as Dump’r) includes resistors
and semiconductors. The latter might
include transistors, diodes, and integrated
circuits.
Any semiconductor is inherently a
nonlinear device. Thus applying a small
forward bias voltage to a diode, for instance,
will result in some current flow through it.
But unlike a resistor, doubling that voltage
will far more than double the current flow.
The voltage/current relationship displayed
by a semiconductor is “curved,” and not a
constant.
Similarly, when an ohmmeter applies a
test current to such a nonlinear device, the
displayed ohms value will be a function of
the instrument’s test current value. Thus a
semiconductor will likely appear as a
changing resistance value with different
meter ranges—and, it turns out, with
different brands and models of DMMs.
In summary, the measured resistance
value of such a circuit/device will likely vary
with the measurement instrument and
instrument range. It’s a case of the
measurement seemingly affecting that which
is being measured.
As it turns out, many DMMs on the
market have remarkably similar operating
characteristics, and most often the expected
value of circuit resistance will be uniformly
(though often meaninglessly) reported by
them. So even the misapplication of a DMM
ohmmeter as in the checkout of a nonlinear
circuit can be useful—and it did work for
most readers.
However, with the large number of
readers building Dump’r, a large number of
DMM product types have been in use. This
has led to some readers experiencing
discrepancies in the circuit resistance
checkout table of values. As this problem
area began to emerge within reader mail, I
confirmed that such can happen by
examining results for 11 DMMs. Two
produced results that differed from the
mainstream expectations (the published
Dump’r table).
I’ll try to address this limitation in any of
my future electronic projects that MA
publishes. In the meantime, if you have
experienced problems with the ohmmeter
checkout of Dump’r (or any other of my
electronic projects), the preceding
explanation may be the reason. If you’ve got
this (or any) checkout problem, please write
and we’ll take it from there.
So concludes one more column. Please
include a self-addressed, stamped
envelope with any correspondence for
which you like a reply. Everyone so doing
does get one. I do not use E-mail for this
purpose. Think “Electric spring”; this, my
favorite time of year, is coming soon (but
not soon enough)! MA
March 2004 127
For more great Focal Point photos, go to: www.modelaircraft.org/mag/index.htm
Edition: Model Aviation - 2004/03
Page Numbers: 125,126,127
Edition: Model Aviation - 2004/03
Page Numbers: 125,126,127
March 2004 125
THIS COLUMN INCLUDES follow-up
on two airplanes discussed in the January
column, adds a third, and discusses more
reader experience with Dump’r, including
the related use of ohmmeters for checkout as
part of the continuing “electrical terms and
concepts” miniseries.
I showed and wrote about the Skyvolt and
Ruckus designs with new AstroFlight
brushless power systems in the January
column. I recently retrofitted my original
Skyvolt, which was published as a
cover/feature in the January 1990 Model
Aviation, with a geared Astro two-turn
brushless 05 motor on eight cells. The
January 2004 column described the huge
difference this up-to-date power system
made; I made a whole new airplane out of
this aging original design.
I described Ruckus as a new original
aerobatic design with a geared Astro threeturn
brushless 05 motor on 10 cells. I’m
having a great time with this airplane, and
now I have four interchangeable packs with
which to fly it. I’ve been tracking Ruckus’s
flight experience for the two months of its
existence, and as of this writing I have
logged 82 flights. One graphic depicts this.
The 10-cell packs include one CP 1.7,
one “old” 2.0, one new 2.4, and one new
matched GP 3.3. The first three packs are
Ni-Cd, and the last is NiMH. Ruckus weighs
less than 51 ounces with the 1.7s and 56-57
ounces with the other three packs.
A typical flight is a continuous mix of
show-off vertical, many consecutive inside
and outside loops, rolls, 8s of all kinds,
knife edge, etc.—all of the normal stuff. All
flights include throttle management
throughout. If you add the averages shown
on the graphic, you’ll see that going to the
field with four charged packs allows me
more than 40 nearly continuous minutes of
air time, by which time I’m tired!
Having been so impressed with these two
Astro motors, I purchased a third—my
second three-turn—and retrofitted it into an
old Revolt! (which was featured in the
November 1994 MA).
The Revolt! is a docile, flat-bottom,
cabin-type model that was originally
designed to accommodate E-experiments
including power-system flight-testing,
telemetry stuff, glitch recorders, etc. Many
readers installed cameras in it. (Revolt! is
extremely versatile.)
This particular Revolt! had a geared
Cobalt 15 on 12 cells and weighed 68.5
ounces. That number dropped to 60.5
ounces with the new motor on 10 cells. As
with the Skyvolt, Revolt! power went way
up and flight duration increased.
The power increase was so dramatic that
brief vertical performance, sustained
inverted flight, and even a (large) outside
loop became possible—despite the flat
section. That’s all because of the enormous
thrust increase combined with the reduced
weight. Another dramatic manifestation was
that I could not touch the sizzling-hot 15
upon landing, but the brushless 05 is barely
warm.
These geared Astro 05 brushless motors
weigh 5.5 ounces and seem comfortable at
upward of 350 watts. My trusty, muchflown,
and much-liked 15 Cobalt is now
paperweight material! And, no, the 15 and
05 nomenclature does not mean anything
Bob Kopski, 25 West End Dr., Lansdale PA 19446
RADIO CONTROL ELECTRICS
Geared (3.3:1) AstroFlight brushless, sensorless 05 motor with older controller. Motor
and newer controller weigh only 7.5 ounces but provide heavy performance!
This provides a closer look at the nifty Astro brushless connector set. Rotating the
connector matchup by 180° changes the motor direction.
126 MODEL AVIATION
useful that I can discern, so don’t even ask!
To complete this story, I’m using a 10 x
5E propeller with the eight-cell/two-turn
system and a 12 x 6E with the 10-cell/threeturn.
My motors have the helical gearbox
option—the classic, robust Astro product
design that holds up well.
All of my installations use Castle
Creations’ Phoenix brushless, sensorless
controls—the 45 or the 60—with BEC
(Battery Eliminator Circuit). These
controllers are programmable for many
operational parameters.
I like using the “soft” cutoff option and
the correct cutoff voltage settings for the
associated cell count. The latter precludes
packs from overdischarge, which is good for
all batteries but critical with Lithium-
Polymer. As I did with the Astro motors, I
expect to buy more Castle controllers soon.
I appreciate that much of this info may
be old news to some readers, but I’m also
sensitive to the fact that many others have
not experienced or even witnessed this sort
of thing. Since I’m about to buy my fourth
geared Astro 05 brushless, it should be
obvious that I wholeheartedly recommend
this product—certainly for the range of
models I’ve described so far, but for others
too, I’m sure.
The Dump’r (featured in the October 2003
MA) continues to bring in a great deal of
reader reaction. By now there must be a
zillion Dump’rs out there! In fact, I’ve heard
that the recommended parts supplier
(Mouser) temporarily sold out of some
parts!
By now it should also be well known that
although the Dump’r design is solid and
works as described, the original article had
some writing mistakes. These were
discussed in the “Letters to the Editor”
section of the December 2003 MA, and I can
supply the details to anyone in need.
Some readers sent me problematic
Dump’rs to troubleshoot. All six I’ve
received suffered from reader-assembly
error, and all worked perfectly when they
were fixed. I discussed some reader
problems in the February 2004 column, and
following are some new ones.
The specified RadioShack PC holeboard,
a portion of which is used in Dump’r, has an
array of “horizontal” busses and two
“vertical” or edge busses. These vertical
stripes alternately connect to the more
numerous horizontal stripes. Interspersed
with this orthagonal buss array are many
isolated three-hole PC lands. (This is easier
to see than to describe.)
Two readers cut out the required board
piece in a way that they unknowingly
included residue of one of the vertical
conductors. This partially cut stripe—still
marginally connected to alternating
horizontal busses—shorted out large
amounts of the Dump’r circuit board. The
fix is easy. Scrape away the offending buss
residue with a #11 X-Acto blade. The
readers’ Dump’rs worked perfectly as soon
as I did this.
Another reader mistakenly wired the
light-emitting diode (LED) backward.
Remember that LEDs have polarity; the
cathode (negative) lead is identified by a
noticeable flat spot on the otherwise round
base.
One reader’s problem was that the fullsize
box layout/drill template drawing in MA
was inaccurate when he copied it. Be sure to
check your copier to make sure it is set to
“full size” or “100%” scale, and then
compare the copy with the original page in
MA to verify dimensional accuracy before
you drill any holes!
Another reader attempted to clear spaces
between PC-board lands with a Dremel tool
and a cutoff wheel. The abrasive wheel
smeared solder between lands and produced
much solder dust. This resulted in massive
board shorts—the very thing he tried to
eliminate! If you need to clear some land-toland
bridges, use a #11 X-Acto, a solvent
(e.g., acetone), and a brush to clean the
board bottom, and inspect all work with a
lens.
Several readers experienced problems
with Dump’r checkout following assembly.
As I do with all of my electronics feature
articles, I included information about
checking out the completed assembly with
an ohmmeter before powering it up.
This seemingly simple step generally
works fine, but a few readers experienced
incorrect readings on otherwise good
Dump’rs. This is a good transition topic into
the miniseries about electrical terms and
concepts that I began several columns ago.
The miniseries discussion in the October
2003 issue was to have an associated
graphic depicting current and voltage
measurements and the use of shunts. That
graphic missed that issue and was presented
in the December issue on page 158. You
need the October column text and the
December graphic to make them both right.
In previous columns I have discussed the
voltmeter and ammeter functions within
digital multimeters (DMMs). Let’s look at
the ohmmeter function. Its purpose is to
measure resistance, and the unit of
resistance is ohms. One ohm is the
resistance value such that if 1 volt were
applied to it, 1 amp would flow.
Ohmmeters are useful primarily in
measuring fixed resistors and can generally
produce accurate readings from low values
(a few ohms) to many millions of ohms
(megohms). This is usually accomplished
with several meter ranges (full scale values).
Typical meter ranges include 200 ohms,
2,000 ohms, 20,000 ohms (20K ohms),
200K ohms, 2 million ohms (2 megohms),
and 20 megohms, but some DMMs have
ranges based on 3s and 4s. Also, some
meters may include extended ranges such as
a 10s scale and/or higher megohm scales.
Resistors are linear devices. For instance,
if in the preceding definition 10 volts were
applied to that 1-ohm resistor, 10 amps
would flow. Thus the current that flows in
any resistor is linearly related to the applied
voltage. So at least within their published
rating limits, resistor values in ohms are
fixed and do not change with the voltage
applied.
Alternately, if a current were
independently made to flow through a
resistor, the resulting voltage appearing on
that resistor would be the current multiplied
by the resistor value. If 1⁄10 amp (100
milliamperes) were forced to flow through a
1-ohm resistor, 1⁄10 volt (100 millivolts)
would appear across it. A 1⁄100-amp (10
milliampere) current would cause 1⁄100 volt
(10 millivolts) to appear on that same 1-ohm
resistor, and a 10-ohm resistor in its place
would yield 10/100 = 1⁄10 volt.
Most digital ohmmeters work using the
latter operational methodology. DMM
ohmmeters work by electronically causing
some fixed current flow through the
unknown resistor and then measuring
(reporting) the resulting voltage disguised as
ohms.
Assume that some ohmmeter set to the
200-ohm scale applies a test current of 1
milliamp to a resistor being measured. If it
happened to be a 100-ohm resistor, 100
millivolts would appear across it. The meter
is designed to translate and display this as
100 ohms.
If the meter range were changed—say to
2K ohms—the meter might apply a reduced
test current of 1⁄10 milliampere. This would
reduce the voltage on the resistor to just 10
millivolts, but the displayed result would still
be the same nominal 100 ohms. However,
the result would be displayed with reduced
resolution (fewer significant figures) like the
example depicted in the September column
for voltage measurements.
Consider applying an ohmmeter as a
circuit-checkout device. A typical electronic
circuit (such as Dump’r) includes resistors
and semiconductors. The latter might
include transistors, diodes, and integrated
circuits.
Any semiconductor is inherently a
nonlinear device. Thus applying a small
forward bias voltage to a diode, for instance,
will result in some current flow through it.
But unlike a resistor, doubling that voltage
will far more than double the current flow.
The voltage/current relationship displayed
by a semiconductor is “curved,” and not a
constant.
Similarly, when an ohmmeter applies a
test current to such a nonlinear device, the
displayed ohms value will be a function of
the instrument’s test current value. Thus a
semiconductor will likely appear as a
changing resistance value with different
meter ranges—and, it turns out, with
different brands and models of DMMs.
In summary, the measured resistance
value of such a circuit/device will likely vary
with the measurement instrument and
instrument range. It’s a case of the
measurement seemingly affecting that which
is being measured.
As it turns out, many DMMs on the
market have remarkably similar operating
characteristics, and most often the expected
value of circuit resistance will be uniformly
(though often meaninglessly) reported by
them. So even the misapplication of a DMM
ohmmeter as in the checkout of a nonlinear
circuit can be useful—and it did work for
most readers.
However, with the large number of
readers building Dump’r, a large number of
DMM product types have been in use. This
has led to some readers experiencing
discrepancies in the circuit resistance
checkout table of values. As this problem
area began to emerge within reader mail, I
confirmed that such can happen by
examining results for 11 DMMs. Two
produced results that differed from the
mainstream expectations (the published
Dump’r table).
I’ll try to address this limitation in any of
my future electronic projects that MA
publishes. In the meantime, if you have
experienced problems with the ohmmeter
checkout of Dump’r (or any other of my
electronic projects), the preceding
explanation may be the reason. If you’ve got
this (or any) checkout problem, please write
and we’ll take it from there.
So concludes one more column. Please
include a self-addressed, stamped
envelope with any correspondence for
which you like a reply. Everyone so doing
does get one. I do not use E-mail for this
purpose. Think “Electric spring”; this, my
favorite time of year, is coming soon (but
not soon enough)! MA
March 2004 127
For more great Focal Point photos, go to: www.modelaircraft.org/mag/index.htm
Edition: Model Aviation - 2004/03
Page Numbers: 125,126,127
March 2004 125
THIS COLUMN INCLUDES follow-up
on two airplanes discussed in the January
column, adds a third, and discusses more
reader experience with Dump’r, including
the related use of ohmmeters for checkout as
part of the continuing “electrical terms and
concepts” miniseries.
I showed and wrote about the Skyvolt and
Ruckus designs with new AstroFlight
brushless power systems in the January
column. I recently retrofitted my original
Skyvolt, which was published as a
cover/feature in the January 1990 Model
Aviation, with a geared Astro two-turn
brushless 05 motor on eight cells. The
January 2004 column described the huge
difference this up-to-date power system
made; I made a whole new airplane out of
this aging original design.
I described Ruckus as a new original
aerobatic design with a geared Astro threeturn
brushless 05 motor on 10 cells. I’m
having a great time with this airplane, and
now I have four interchangeable packs with
which to fly it. I’ve been tracking Ruckus’s
flight experience for the two months of its
existence, and as of this writing I have
logged 82 flights. One graphic depicts this.
The 10-cell packs include one CP 1.7,
one “old” 2.0, one new 2.4, and one new
matched GP 3.3. The first three packs are
Ni-Cd, and the last is NiMH. Ruckus weighs
less than 51 ounces with the 1.7s and 56-57
ounces with the other three packs.
A typical flight is a continuous mix of
show-off vertical, many consecutive inside
and outside loops, rolls, 8s of all kinds,
knife edge, etc.—all of the normal stuff. All
flights include throttle management
throughout. If you add the averages shown
on the graphic, you’ll see that going to the
field with four charged packs allows me
more than 40 nearly continuous minutes of
air time, by which time I’m tired!
Having been so impressed with these two
Astro motors, I purchased a third—my
second three-turn—and retrofitted it into an
old Revolt! (which was featured in the
November 1994 MA).
The Revolt! is a docile, flat-bottom,
cabin-type model that was originally
designed to accommodate E-experiments
including power-system flight-testing,
telemetry stuff, glitch recorders, etc. Many
readers installed cameras in it. (Revolt! is
extremely versatile.)
This particular Revolt! had a geared
Cobalt 15 on 12 cells and weighed 68.5
ounces. That number dropped to 60.5
ounces with the new motor on 10 cells. As
with the Skyvolt, Revolt! power went way
up and flight duration increased.
The power increase was so dramatic that
brief vertical performance, sustained
inverted flight, and even a (large) outside
loop became possible—despite the flat
section. That’s all because of the enormous
thrust increase combined with the reduced
weight. Another dramatic manifestation was
that I could not touch the sizzling-hot 15
upon landing, but the brushless 05 is barely
warm.
These geared Astro 05 brushless motors
weigh 5.5 ounces and seem comfortable at
upward of 350 watts. My trusty, muchflown,
and much-liked 15 Cobalt is now
paperweight material! And, no, the 15 and
05 nomenclature does not mean anything
Bob Kopski, 25 West End Dr., Lansdale PA 19446
RADIO CONTROL ELECTRICS
Geared (3.3:1) AstroFlight brushless, sensorless 05 motor with older controller. Motor
and newer controller weigh only 7.5 ounces but provide heavy performance!
This provides a closer look at the nifty Astro brushless connector set. Rotating the
connector matchup by 180° changes the motor direction.
126 MODEL AVIATION
useful that I can discern, so don’t even ask!
To complete this story, I’m using a 10 x
5E propeller with the eight-cell/two-turn
system and a 12 x 6E with the 10-cell/threeturn.
My motors have the helical gearbox
option—the classic, robust Astro product
design that holds up well.
All of my installations use Castle
Creations’ Phoenix brushless, sensorless
controls—the 45 or the 60—with BEC
(Battery Eliminator Circuit). These
controllers are programmable for many
operational parameters.
I like using the “soft” cutoff option and
the correct cutoff voltage settings for the
associated cell count. The latter precludes
packs from overdischarge, which is good for
all batteries but critical with Lithium-
Polymer. As I did with the Astro motors, I
expect to buy more Castle controllers soon.
I appreciate that much of this info may
be old news to some readers, but I’m also
sensitive to the fact that many others have
not experienced or even witnessed this sort
of thing. Since I’m about to buy my fourth
geared Astro 05 brushless, it should be
obvious that I wholeheartedly recommend
this product—certainly for the range of
models I’ve described so far, but for others
too, I’m sure.
The Dump’r (featured in the October 2003
MA) continues to bring in a great deal of
reader reaction. By now there must be a
zillion Dump’rs out there! In fact, I’ve heard
that the recommended parts supplier
(Mouser) temporarily sold out of some
parts!
By now it should also be well known that
although the Dump’r design is solid and
works as described, the original article had
some writing mistakes. These were
discussed in the “Letters to the Editor”
section of the December 2003 MA, and I can
supply the details to anyone in need.
Some readers sent me problematic
Dump’rs to troubleshoot. All six I’ve
received suffered from reader-assembly
error, and all worked perfectly when they
were fixed. I discussed some reader
problems in the February 2004 column, and
following are some new ones.
The specified RadioShack PC holeboard,
a portion of which is used in Dump’r, has an
array of “horizontal” busses and two
“vertical” or edge busses. These vertical
stripes alternately connect to the more
numerous horizontal stripes. Interspersed
with this orthagonal buss array are many
isolated three-hole PC lands. (This is easier
to see than to describe.)
Two readers cut out the required board
piece in a way that they unknowingly
included residue of one of the vertical
conductors. This partially cut stripe—still
marginally connected to alternating
horizontal busses—shorted out large
amounts of the Dump’r circuit board. The
fix is easy. Scrape away the offending buss
residue with a #11 X-Acto blade. The
readers’ Dump’rs worked perfectly as soon
as I did this.
Another reader mistakenly wired the
light-emitting diode (LED) backward.
Remember that LEDs have polarity; the
cathode (negative) lead is identified by a
noticeable flat spot on the otherwise round
base.
One reader’s problem was that the fullsize
box layout/drill template drawing in MA
was inaccurate when he copied it. Be sure to
check your copier to make sure it is set to
“full size” or “100%” scale, and then
compare the copy with the original page in
MA to verify dimensional accuracy before
you drill any holes!
Another reader attempted to clear spaces
between PC-board lands with a Dremel tool
and a cutoff wheel. The abrasive wheel
smeared solder between lands and produced
much solder dust. This resulted in massive
board shorts—the very thing he tried to
eliminate! If you need to clear some land-toland
bridges, use a #11 X-Acto, a solvent
(e.g., acetone), and a brush to clean the
board bottom, and inspect all work with a
lens.
Several readers experienced problems
with Dump’r checkout following assembly.
As I do with all of my electronics feature
articles, I included information about
checking out the completed assembly with
an ohmmeter before powering it up.
This seemingly simple step generally
works fine, but a few readers experienced
incorrect readings on otherwise good
Dump’rs. This is a good transition topic into
the miniseries about electrical terms and
concepts that I began several columns ago.
The miniseries discussion in the October
2003 issue was to have an associated
graphic depicting current and voltage
measurements and the use of shunts. That
graphic missed that issue and was presented
in the December issue on page 158. You
need the October column text and the
December graphic to make them both right.
In previous columns I have discussed the
voltmeter and ammeter functions within
digital multimeters (DMMs). Let’s look at
the ohmmeter function. Its purpose is to
measure resistance, and the unit of
resistance is ohms. One ohm is the
resistance value such that if 1 volt were
applied to it, 1 amp would flow.
Ohmmeters are useful primarily in
measuring fixed resistors and can generally
produce accurate readings from low values
(a few ohms) to many millions of ohms
(megohms). This is usually accomplished
with several meter ranges (full scale values).
Typical meter ranges include 200 ohms,
2,000 ohms, 20,000 ohms (20K ohms),
200K ohms, 2 million ohms (2 megohms),
and 20 megohms, but some DMMs have
ranges based on 3s and 4s. Also, some
meters may include extended ranges such as
a 10s scale and/or higher megohm scales.
Resistors are linear devices. For instance,
if in the preceding definition 10 volts were
applied to that 1-ohm resistor, 10 amps
would flow. Thus the current that flows in
any resistor is linearly related to the applied
voltage. So at least within their published
rating limits, resistor values in ohms are
fixed and do not change with the voltage
applied.
Alternately, if a current were
independently made to flow through a
resistor, the resulting voltage appearing on
that resistor would be the current multiplied
by the resistor value. If 1⁄10 amp (100
milliamperes) were forced to flow through a
1-ohm resistor, 1⁄10 volt (100 millivolts)
would appear across it. A 1⁄100-amp (10
milliampere) current would cause 1⁄100 volt
(10 millivolts) to appear on that same 1-ohm
resistor, and a 10-ohm resistor in its place
would yield 10/100 = 1⁄10 volt.
Most digital ohmmeters work using the
latter operational methodology. DMM
ohmmeters work by electronically causing
some fixed current flow through the
unknown resistor and then measuring
(reporting) the resulting voltage disguised as
ohms.
Assume that some ohmmeter set to the
200-ohm scale applies a test current of 1
milliamp to a resistor being measured. If it
happened to be a 100-ohm resistor, 100
millivolts would appear across it. The meter
is designed to translate and display this as
100 ohms.
If the meter range were changed—say to
2K ohms—the meter might apply a reduced
test current of 1⁄10 milliampere. This would
reduce the voltage on the resistor to just 10
millivolts, but the displayed result would still
be the same nominal 100 ohms. However,
the result would be displayed with reduced
resolution (fewer significant figures) like the
example depicted in the September column
for voltage measurements.
Consider applying an ohmmeter as a
circuit-checkout device. A typical electronic
circuit (such as Dump’r) includes resistors
and semiconductors. The latter might
include transistors, diodes, and integrated
circuits.
Any semiconductor is inherently a
nonlinear device. Thus applying a small
forward bias voltage to a diode, for instance,
will result in some current flow through it.
But unlike a resistor, doubling that voltage
will far more than double the current flow.
The voltage/current relationship displayed
by a semiconductor is “curved,” and not a
constant.
Similarly, when an ohmmeter applies a
test current to such a nonlinear device, the
displayed ohms value will be a function of
the instrument’s test current value. Thus a
semiconductor will likely appear as a
changing resistance value with different
meter ranges—and, it turns out, with
different brands and models of DMMs.
In summary, the measured resistance
value of such a circuit/device will likely vary
with the measurement instrument and
instrument range. It’s a case of the
measurement seemingly affecting that which
is being measured.
As it turns out, many DMMs on the
market have remarkably similar operating
characteristics, and most often the expected
value of circuit resistance will be uniformly
(though often meaninglessly) reported by
them. So even the misapplication of a DMM
ohmmeter as in the checkout of a nonlinear
circuit can be useful—and it did work for
most readers.
However, with the large number of
readers building Dump’r, a large number of
DMM product types have been in use. This
has led to some readers experiencing
discrepancies in the circuit resistance
checkout table of values. As this problem
area began to emerge within reader mail, I
confirmed that such can happen by
examining results for 11 DMMs. Two
produced results that differed from the
mainstream expectations (the published
Dump’r table).
I’ll try to address this limitation in any of
my future electronic projects that MA
publishes. In the meantime, if you have
experienced problems with the ohmmeter
checkout of Dump’r (or any other of my
electronic projects), the preceding
explanation may be the reason. If you’ve got
this (or any) checkout problem, please write
and we’ll take it from there.
So concludes one more column. Please
include a self-addressed, stamped
envelope with any correspondence for
which you like a reply. Everyone so doing
does get one. I do not use E-mail for this
purpose. Think “Electric spring”; this, my
favorite time of year, is coming soon (but
not soon enough)! MA
March 2004 127
For more great Focal Point photos, go to: www.modelaircraft.org/mag/index.htm
