106 MODEL AVIATION
Has your favorite cordless power tool taken a dive?
The Battery Clinic Red Scholefield | [email protected]
Also included in this column:
• Messy charger-cord solution
• Charging A123s in your
airplane
• Checking an RC system
under load
• How much motor do you
need?
• Wire-length conditions
• The diverse modeling
factions
An A123 battery pack finds a place in the renovation of a Skil
screwdriver.
Ryobi’s 12-volt Lithium pack powers a Kavan starter.
The Ryobi Lithium 12-volt drill pack.
A Makita drill gets a new
NoBS battery pack.
A MODELING BUDDY lamented that
his little Makita drill would no longer do
its tasks. We found that NoBS Batteries
will make a replacement pack for your
tired tool that you can drop in and
reconnect with little effort besides taking
out the screws, unsoldering the old pack,
and soldering in the new one.
You will need a Torx T-8 driver for
some tools; you should already have one in
your toolbox. (Sears has some good ones.)
The packs are supplied with solder tabs.
These tools are frequently supplied with
hard-to-find 4/5 C cells, and there is little
tolerance in the tool to allow for your own
assembly, even if you can find the cells.
I have since rebatteried my cordless
screwdriver with a NoBS custom pack. Get
in touch with Steve Anthony at NoBS
Batteries and tell him what you need; it’s
05sig4.QXD 3/25/08 9:23 AM Page 106
108 MODEL AVIATION
PVC pipe cleans up the author’s charger-cord mess.
A simple harness allows you to monitor pack performance.
best to E-mail him the description and
dimensions of your battery because he is
busy and hates to waste time answering
phone calls.
A buddy gave me a Skil screwdriver,
saying that the replacement packs (if he
could even find them) cost more than the
tool. The screwdriver has a removable,
three-cell Ni-Cd pack. I found that its
outside dimensions are the same as an
A123 cell. Hmm. Could I use one to
replace the Ni-Cd pack, same voltage?
When I opened the screwdriver I found
that I could bend the contacts so they fit
the A123 nicely, making contact with the
negative end and the positive can (after
removing a section of insulation). Cutting
off the end of the Ni-Cd battery case
enabled me to reinsert it to hold the A123
firmly in place.
It’s easy to remove for recharging,
which is done with one of my Lithium
chargers. Now I have a field screwdriver,
for putting in wing bolts, that won’t need
charging for several months.
Sometimes figuring out how to get the
tool apart is the biggest problem. Look for
screws hidden under labels. You can feel
around on the label, looking for a soft spot
where the screw might be.
The joint where the Skil driver could
be bent to form a sort of pistol grip had a
cap (labeled “3.6V”) that I was able to
remove to get to a screw that held it all
together. Two easy-to-remove, metal, Ushaped
clips held the other end of the
handle together.
Ryobi has just come out with a 12-volt
Lithium drill (with two packs) that a club
member found made a great pack for his
Kavan starter. He made an adapter that the
pack could plug directly into without
modification. The charger that comes with
the drill takes care of recharging.
Messy Charger Cords? After too many
years of seeing a rat’s nest of charger
cords on my transmitter charging station, I
decided to do something about it. The
question was, what?
Then it hit me; now that I’m using all
electric power, I have little use for the
receiver connectors. But I was hesitant to
cut them off.
I solved the problem with a 4-inch
section of thin-walled, 3/4-inch PVC pipe.
I coiled the cords, leaving out just enough
to connect to the transmitter. I stuffed the
coil, along with the receiver connector,
into the PVC.
Leaving A123 Packs in Your Model
While Charging: With the volatility of Li-
Poly packs, leaving them in your model
for storage or charging is frowned upon.
However, A123 packs are a different
story.
When leaving these batteries in an
airplane for charging, consider that these
cells have been in fairly wide use in our
hobby for nearly two years. There have
been no reported incidents with A123
packs in that time, and a great deal of
charging was done before manufacturers
such as FMA Direct Cellpro, Bantam, and
Xtrema offered chargers that are
specifically tailored to accommodate A123
technology.
With the threat A123 presents to those
who are marketing conventional Li-Poly
batteries, any incident, no matter how
small, would have gotten front-page
billing. The A123 cells present no more of
a hazard than we faced with Ni-Cd packs
we have left in our models for the past 50
years.
Checking Your System Under Load:
Gene A. Morse wrote:
“With most of my systems being
Spektrum ... and a lot of digital systems
commonly being used in our hobby, it is
more critical than ever before, that a ‘Low
Voltage’ or ‘High Amp’ condition doesn’t
occur during a flight. This ‘Test-Harness’
is one of the ways you can help ensure that
the receiver battery pack in your RC is
doing its job well.
“Using this setup ... I found one bad
battery-pack, and 1 questionable servo ( ...
but that was from trying it on only two
set-ups so far). Along with the ‘Test-
Harness’ I used two cheap Wal-Mart
autoranging digital meters ( ... since I
didn’t know exactly what the amp ranges
Connector
to mate
with battery
pack
Connector
to mate
with
receiver or
switch
harness
to this neat bundle ➞
using 3/4-inch PVC pipe
From this rat’s nest... ➞
05sig4.QXD 3/25/08 9:25 AM Page 108
110 MODEL AVIATION
would be). You could easily use one
meter, analog or digital, but it will take
twice as long.
“For single meter a piece of plastic
tubing is used to keep from shorting the +
and – leads (plug them snugly into each
end of the plastic tubing, ensure it’s long
enough so that the banana plugs don’t
touch inside the tubing). A female-tofemale
adapter made from 3/16 D brass
tubing covered with heat shrink,
completes the circuit when an amp meter
is not in line with the harness).
“Begin the test with a fully charged
battery pack, in a flight ready RC (don’t
forget to connect the wing servos). Install
the harness between the battery-pack and
the receiver. You will want to run the test
for, or longer than, the equivalent time of
the RC’s preflight, engine-run and tuning,
the flight and the taxi from the field.
“I started by first driving each
individual servo fully in each direction,
and monitoring the amp draw ( ... this is
how I found the questionable servo, more
than double the amp draw of other ‘Like’
servos). Then I started banging the sticks
... every imaginable single and multiple
combination my thumbs could imagine.
“I continued this for just over 10
minutes. I watched the volt and amp level
for the entire time of the test to ensure the
battery pack could provide the power
needed to work well.
“You want to ensure that the voltage
never drops below the MFG recommended
voltage, and that the amp draw is never
greater than the MFG recommended amp
draw.”
Glow-to-Electric Conversion—How
Much Motor Do I Need? I gleaned some
interesting material from an online
discussion. To start with, 746 watts is
equal to 1 horsepower. Many brushless
motors give watts as a rating. (If not, you
can calculate it by multiplying volts by
amps.) Divide the watts by 746 and you
have the horsepower. This is a good way,
but it has some caveats.
Not all motors have the same
efficiency, so a 50% 200-watt motor
produces only 100 watts at the shaft, etc.
Glow engines produce their power at high
rpm—typically well above the optimum
for propeller efficiency. Therefore, most
glow models (200 mph stuff excepted) run
at suboptimal rpm and at considerably less
power than the motor is capable of
producing.
Also, since electric motors tend—in
the case of outrunners or geared types—to
deliver power at a more sensible rpm into
a bigger propeller, the electric power to
match an “hp glow” may be less than 300
watts.
With these caveats, this rule of thumb
has considerable merit if you accept that
an input of approximately 2 kilowatts per
cu. in. is a decent enough guide, which
places a .40 glow at roughly 800 watts
input. The other way is to use the watts/
pound formula and pick a propeller whose
pitch speed (there is a convenient
calculator online) loads the motor to its
rated current draw and is two-and-a-half
to three times the stall speed.
If you want sporty performance, 75-
100 watts per pound is a decent target. I
have found that a typical 5-pound glow
model running at 800 watts is sporty
indeed.
Lead Length Between Motor and ESC
and Battery and ESC: Paul Yee Patrick
(Castle Creations) wrote:
“On the HV controllers especially, the
battery-ESC length is the critical length.
You should not extend the wires more
than a total length of greater than 12
inches without additional capacitors.”
On the motor side, length is less
critical; 18 inches is fine.
“You must keep battery wires (to ESC)
as short as practical,” according to
AstroFlight. “Short means 1 foot or less.
Brushed or brushless makes no
difference.”
From ESC to motor, wire inductance
will not damage your motor, nor will you
be able to detect any effect, even with 100
feet of wire.
Modeling Groups: Judging from the Emails
I get and what I read on various
Internet modeling forums, it appears that
modelers who use computers reflect the
general modeling population. They have
the same questions, the same concerns,
and the same opinions. So what are online
modelers deliberating on or debating?
The thread that comes through is that
there are two distinct groups of modelers,
one of which I call the “What’s in it for
me?” crowd. RC is just “there,” as are
VCRs, television, and Monday Night
Football—theirs for the taking without a
clue about what is required to make it
happen.
The other group has a broader, longer
range of thinking and philosophy that
tends to support more organized modeling
activities, even though they are at violent
odds at times with how the organizations
are approaching the complex subject of
tending to the needs of the modeling
fraternity. If one can keep his or her
perspective, this makes for great
discussions.
That’s it for this month. Support your US
Postal Service and write to me (send an
SASE if you want a personalized answer)
at The Battery Clinic, 12219 NW 9th Ln.,
Newberry FL 32669. E-mail is faster. MA
Sources:
Gene A. Morse
[email protected]
NoBS Batteries
(631) 610-5169
[email protected]
www.hangtimes.com/nobsbatteries.html
Propeller pitch speed calculator
www.rcpro.org/rccalc/PitchSpeed.aspx
Contact
AMA’s Supply & Service Department
for your Product Guide needs
Call (765) 287-1256, extension 212, or visit the AMA Web site at
www.modelaircraft.org. Click on “Shop AMA” to browse the
catalog for the newest merchandise and the best deals on closeout items.
05sig4.QXD 3/25/08 9:25 AM Page 110
Edition: Model Aviation - 2008/05
Page Numbers: 106,108
Edition: Model Aviation - 2008/05
Page Numbers: 106,108
106 MODEL AVIATION
Has your favorite cordless power tool taken a dive?
The Battery Clinic Red Scholefield | [email protected]
Also included in this column:
• Messy charger-cord solution
• Charging A123s in your
airplane
• Checking an RC system
under load
• How much motor do you
need?
• Wire-length conditions
• The diverse modeling
factions
An A123 battery pack finds a place in the renovation of a Skil
screwdriver.
Ryobi’s 12-volt Lithium pack powers a Kavan starter.
The Ryobi Lithium 12-volt drill pack.
A Makita drill gets a new
NoBS battery pack.
A MODELING BUDDY lamented that
his little Makita drill would no longer do
its tasks. We found that NoBS Batteries
will make a replacement pack for your
tired tool that you can drop in and
reconnect with little effort besides taking
out the screws, unsoldering the old pack,
and soldering in the new one.
You will need a Torx T-8 driver for
some tools; you should already have one in
your toolbox. (Sears has some good ones.)
The packs are supplied with solder tabs.
These tools are frequently supplied with
hard-to-find 4/5 C cells, and there is little
tolerance in the tool to allow for your own
assembly, even if you can find the cells.
I have since rebatteried my cordless
screwdriver with a NoBS custom pack. Get
in touch with Steve Anthony at NoBS
Batteries and tell him what you need; it’s
05sig4.QXD 3/25/08 9:23 AM Page 106
108 MODEL AVIATION
PVC pipe cleans up the author’s charger-cord mess.
A simple harness allows you to monitor pack performance.
best to E-mail him the description and
dimensions of your battery because he is
busy and hates to waste time answering
phone calls.
A buddy gave me a Skil screwdriver,
saying that the replacement packs (if he
could even find them) cost more than the
tool. The screwdriver has a removable,
three-cell Ni-Cd pack. I found that its
outside dimensions are the same as an
A123 cell. Hmm. Could I use one to
replace the Ni-Cd pack, same voltage?
When I opened the screwdriver I found
that I could bend the contacts so they fit
the A123 nicely, making contact with the
negative end and the positive can (after
removing a section of insulation). Cutting
off the end of the Ni-Cd battery case
enabled me to reinsert it to hold the A123
firmly in place.
It’s easy to remove for recharging,
which is done with one of my Lithium
chargers. Now I have a field screwdriver,
for putting in wing bolts, that won’t need
charging for several months.
Sometimes figuring out how to get the
tool apart is the biggest problem. Look for
screws hidden under labels. You can feel
around on the label, looking for a soft spot
where the screw might be.
The joint where the Skil driver could
be bent to form a sort of pistol grip had a
cap (labeled “3.6V”) that I was able to
remove to get to a screw that held it all
together. Two easy-to-remove, metal, Ushaped
clips held the other end of the
handle together.
Ryobi has just come out with a 12-volt
Lithium drill (with two packs) that a club
member found made a great pack for his
Kavan starter. He made an adapter that the
pack could plug directly into without
modification. The charger that comes with
the drill takes care of recharging.
Messy Charger Cords? After too many
years of seeing a rat’s nest of charger
cords on my transmitter charging station, I
decided to do something about it. The
question was, what?
Then it hit me; now that I’m using all
electric power, I have little use for the
receiver connectors. But I was hesitant to
cut them off.
I solved the problem with a 4-inch
section of thin-walled, 3/4-inch PVC pipe.
I coiled the cords, leaving out just enough
to connect to the transmitter. I stuffed the
coil, along with the receiver connector,
into the PVC.
Leaving A123 Packs in Your Model
While Charging: With the volatility of Li-
Poly packs, leaving them in your model
for storage or charging is frowned upon.
However, A123 packs are a different
story.
When leaving these batteries in an
airplane for charging, consider that these
cells have been in fairly wide use in our
hobby for nearly two years. There have
been no reported incidents with A123
packs in that time, and a great deal of
charging was done before manufacturers
such as FMA Direct Cellpro, Bantam, and
Xtrema offered chargers that are
specifically tailored to accommodate A123
technology.
With the threat A123 presents to those
who are marketing conventional Li-Poly
batteries, any incident, no matter how
small, would have gotten front-page
billing. The A123 cells present no more of
a hazard than we faced with Ni-Cd packs
we have left in our models for the past 50
years.
Checking Your System Under Load:
Gene A. Morse wrote:
“With most of my systems being
Spektrum ... and a lot of digital systems
commonly being used in our hobby, it is
more critical than ever before, that a ‘Low
Voltage’ or ‘High Amp’ condition doesn’t
occur during a flight. This ‘Test-Harness’
is one of the ways you can help ensure that
the receiver battery pack in your RC is
doing its job well.
“Using this setup ... I found one bad
battery-pack, and 1 questionable servo ( ...
but that was from trying it on only two
set-ups so far). Along with the ‘Test-
Harness’ I used two cheap Wal-Mart
autoranging digital meters ( ... since I
didn’t know exactly what the amp ranges
Connector
to mate
with battery
pack
Connector
to mate
with
receiver or
switch
harness
to this neat bundle ➞
using 3/4-inch PVC pipe
From this rat’s nest... ➞
05sig4.QXD 3/25/08 9:25 AM Page 108
110 MODEL AVIATION
would be). You could easily use one
meter, analog or digital, but it will take
twice as long.
“For single meter a piece of plastic
tubing is used to keep from shorting the +
and – leads (plug them snugly into each
end of the plastic tubing, ensure it’s long
enough so that the banana plugs don’t
touch inside the tubing). A female-tofemale
adapter made from 3/16 D brass
tubing covered with heat shrink,
completes the circuit when an amp meter
is not in line with the harness).
“Begin the test with a fully charged
battery pack, in a flight ready RC (don’t
forget to connect the wing servos). Install
the harness between the battery-pack and
the receiver. You will want to run the test
for, or longer than, the equivalent time of
the RC’s preflight, engine-run and tuning,
the flight and the taxi from the field.
“I started by first driving each
individual servo fully in each direction,
and monitoring the amp draw ( ... this is
how I found the questionable servo, more
than double the amp draw of other ‘Like’
servos). Then I started banging the sticks
... every imaginable single and multiple
combination my thumbs could imagine.
“I continued this for just over 10
minutes. I watched the volt and amp level
for the entire time of the test to ensure the
battery pack could provide the power
needed to work well.
“You want to ensure that the voltage
never drops below the MFG recommended
voltage, and that the amp draw is never
greater than the MFG recommended amp
draw.”
Glow-to-Electric Conversion—How
Much Motor Do I Need? I gleaned some
interesting material from an online
discussion. To start with, 746 watts is
equal to 1 horsepower. Many brushless
motors give watts as a rating. (If not, you
can calculate it by multiplying volts by
amps.) Divide the watts by 746 and you
have the horsepower. This is a good way,
but it has some caveats.
Not all motors have the same
efficiency, so a 50% 200-watt motor
produces only 100 watts at the shaft, etc.
Glow engines produce their power at high
rpm—typically well above the optimum
for propeller efficiency. Therefore, most
glow models (200 mph stuff excepted) run
at suboptimal rpm and at considerably less
power than the motor is capable of
producing.
Also, since electric motors tend—in
the case of outrunners or geared types—to
deliver power at a more sensible rpm into
a bigger propeller, the electric power to
match an “hp glow” may be less than 300
watts.
With these caveats, this rule of thumb
has considerable merit if you accept that
an input of approximately 2 kilowatts per
cu. in. is a decent enough guide, which
places a .40 glow at roughly 800 watts
input. The other way is to use the watts/
pound formula and pick a propeller whose
pitch speed (there is a convenient
calculator online) loads the motor to its
rated current draw and is two-and-a-half
to three times the stall speed.
If you want sporty performance, 75-
100 watts per pound is a decent target. I
have found that a typical 5-pound glow
model running at 800 watts is sporty
indeed.
Lead Length Between Motor and ESC
and Battery and ESC: Paul Yee Patrick
(Castle Creations) wrote:
“On the HV controllers especially, the
battery-ESC length is the critical length.
You should not extend the wires more
than a total length of greater than 12
inches without additional capacitors.”
On the motor side, length is less
critical; 18 inches is fine.
“You must keep battery wires (to ESC)
as short as practical,” according to
AstroFlight. “Short means 1 foot or less.
Brushed or brushless makes no
difference.”
From ESC to motor, wire inductance
will not damage your motor, nor will you
be able to detect any effect, even with 100
feet of wire.
Modeling Groups: Judging from the Emails
I get and what I read on various
Internet modeling forums, it appears that
modelers who use computers reflect the
general modeling population. They have
the same questions, the same concerns,
and the same opinions. So what are online
modelers deliberating on or debating?
The thread that comes through is that
there are two distinct groups of modelers,
one of which I call the “What’s in it for
me?” crowd. RC is just “there,” as are
VCRs, television, and Monday Night
Football—theirs for the taking without a
clue about what is required to make it
happen.
The other group has a broader, longer
range of thinking and philosophy that
tends to support more organized modeling
activities, even though they are at violent
odds at times with how the organizations
are approaching the complex subject of
tending to the needs of the modeling
fraternity. If one can keep his or her
perspective, this makes for great
discussions.
That’s it for this month. Support your US
Postal Service and write to me (send an
SASE if you want a personalized answer)
at The Battery Clinic, 12219 NW 9th Ln.,
Newberry FL 32669. E-mail is faster. MA
Sources:
Gene A. Morse
[email protected]
NoBS Batteries
(631) 610-5169
[email protected]
www.hangtimes.com/nobsbatteries.html
Propeller pitch speed calculator
www.rcpro.org/rccalc/PitchSpeed.aspx
Contact
AMA’s Supply & Service Department
for your Product Guide needs
Call (765) 287-1256, extension 212, or visit the AMA Web site at
www.modelaircraft.org. Click on “Shop AMA” to browse the
catalog for the newest merchandise and the best deals on closeout items.
05sig4.QXD 3/25/08 9:25 AM Page 110
Edition: Model Aviation - 2008/05
Page Numbers: 106,108
106 MODEL AVIATION
Has your favorite cordless power tool taken a dive?
The Battery Clinic Red Scholefield | [email protected]
Also included in this column:
• Messy charger-cord solution
• Charging A123s in your
airplane
• Checking an RC system
under load
• How much motor do you
need?
• Wire-length conditions
• The diverse modeling
factions
An A123 battery pack finds a place in the renovation of a Skil
screwdriver.
Ryobi’s 12-volt Lithium pack powers a Kavan starter.
The Ryobi Lithium 12-volt drill pack.
A Makita drill gets a new
NoBS battery pack.
A MODELING BUDDY lamented that
his little Makita drill would no longer do
its tasks. We found that NoBS Batteries
will make a replacement pack for your
tired tool that you can drop in and
reconnect with little effort besides taking
out the screws, unsoldering the old pack,
and soldering in the new one.
You will need a Torx T-8 driver for
some tools; you should already have one in
your toolbox. (Sears has some good ones.)
The packs are supplied with solder tabs.
These tools are frequently supplied with
hard-to-find 4/5 C cells, and there is little
tolerance in the tool to allow for your own
assembly, even if you can find the cells.
I have since rebatteried my cordless
screwdriver with a NoBS custom pack. Get
in touch with Steve Anthony at NoBS
Batteries and tell him what you need; it’s
05sig4.QXD 3/25/08 9:23 AM Page 106
108 MODEL AVIATION
PVC pipe cleans up the author’s charger-cord mess.
A simple harness allows you to monitor pack performance.
best to E-mail him the description and
dimensions of your battery because he is
busy and hates to waste time answering
phone calls.
A buddy gave me a Skil screwdriver,
saying that the replacement packs (if he
could even find them) cost more than the
tool. The screwdriver has a removable,
three-cell Ni-Cd pack. I found that its
outside dimensions are the same as an
A123 cell. Hmm. Could I use one to
replace the Ni-Cd pack, same voltage?
When I opened the screwdriver I found
that I could bend the contacts so they fit
the A123 nicely, making contact with the
negative end and the positive can (after
removing a section of insulation). Cutting
off the end of the Ni-Cd battery case
enabled me to reinsert it to hold the A123
firmly in place.
It’s easy to remove for recharging,
which is done with one of my Lithium
chargers. Now I have a field screwdriver,
for putting in wing bolts, that won’t need
charging for several months.
Sometimes figuring out how to get the
tool apart is the biggest problem. Look for
screws hidden under labels. You can feel
around on the label, looking for a soft spot
where the screw might be.
The joint where the Skil driver could
be bent to form a sort of pistol grip had a
cap (labeled “3.6V”) that I was able to
remove to get to a screw that held it all
together. Two easy-to-remove, metal, Ushaped
clips held the other end of the
handle together.
Ryobi has just come out with a 12-volt
Lithium drill (with two packs) that a club
member found made a great pack for his
Kavan starter. He made an adapter that the
pack could plug directly into without
modification. The charger that comes with
the drill takes care of recharging.
Messy Charger Cords? After too many
years of seeing a rat’s nest of charger
cords on my transmitter charging station, I
decided to do something about it. The
question was, what?
Then it hit me; now that I’m using all
electric power, I have little use for the
receiver connectors. But I was hesitant to
cut them off.
I solved the problem with a 4-inch
section of thin-walled, 3/4-inch PVC pipe.
I coiled the cords, leaving out just enough
to connect to the transmitter. I stuffed the
coil, along with the receiver connector,
into the PVC.
Leaving A123 Packs in Your Model
While Charging: With the volatility of Li-
Poly packs, leaving them in your model
for storage or charging is frowned upon.
However, A123 packs are a different
story.
When leaving these batteries in an
airplane for charging, consider that these
cells have been in fairly wide use in our
hobby for nearly two years. There have
been no reported incidents with A123
packs in that time, and a great deal of
charging was done before manufacturers
such as FMA Direct Cellpro, Bantam, and
Xtrema offered chargers that are
specifically tailored to accommodate A123
technology.
With the threat A123 presents to those
who are marketing conventional Li-Poly
batteries, any incident, no matter how
small, would have gotten front-page
billing. The A123 cells present no more of
a hazard than we faced with Ni-Cd packs
we have left in our models for the past 50
years.
Checking Your System Under Load:
Gene A. Morse wrote:
“With most of my systems being
Spektrum ... and a lot of digital systems
commonly being used in our hobby, it is
more critical than ever before, that a ‘Low
Voltage’ or ‘High Amp’ condition doesn’t
occur during a flight. This ‘Test-Harness’
is one of the ways you can help ensure that
the receiver battery pack in your RC is
doing its job well.
“Using this setup ... I found one bad
battery-pack, and 1 questionable servo ( ...
but that was from trying it on only two
set-ups so far). Along with the ‘Test-
Harness’ I used two cheap Wal-Mart
autoranging digital meters ( ... since I
didn’t know exactly what the amp ranges
Connector
to mate
with battery
pack
Connector
to mate
with
receiver or
switch
harness
to this neat bundle ➞
using 3/4-inch PVC pipe
From this rat’s nest... ➞
05sig4.QXD 3/25/08 9:25 AM Page 108
110 MODEL AVIATION
would be). You could easily use one
meter, analog or digital, but it will take
twice as long.
“For single meter a piece of plastic
tubing is used to keep from shorting the +
and – leads (plug them snugly into each
end of the plastic tubing, ensure it’s long
enough so that the banana plugs don’t
touch inside the tubing). A female-tofemale
adapter made from 3/16 D brass
tubing covered with heat shrink,
completes the circuit when an amp meter
is not in line with the harness).
“Begin the test with a fully charged
battery pack, in a flight ready RC (don’t
forget to connect the wing servos). Install
the harness between the battery-pack and
the receiver. You will want to run the test
for, or longer than, the equivalent time of
the RC’s preflight, engine-run and tuning,
the flight and the taxi from the field.
“I started by first driving each
individual servo fully in each direction,
and monitoring the amp draw ( ... this is
how I found the questionable servo, more
than double the amp draw of other ‘Like’
servos). Then I started banging the sticks
... every imaginable single and multiple
combination my thumbs could imagine.
“I continued this for just over 10
minutes. I watched the volt and amp level
for the entire time of the test to ensure the
battery pack could provide the power
needed to work well.
“You want to ensure that the voltage
never drops below the MFG recommended
voltage, and that the amp draw is never
greater than the MFG recommended amp
draw.”
Glow-to-Electric Conversion—How
Much Motor Do I Need? I gleaned some
interesting material from an online
discussion. To start with, 746 watts is
equal to 1 horsepower. Many brushless
motors give watts as a rating. (If not, you
can calculate it by multiplying volts by
amps.) Divide the watts by 746 and you
have the horsepower. This is a good way,
but it has some caveats.
Not all motors have the same
efficiency, so a 50% 200-watt motor
produces only 100 watts at the shaft, etc.
Glow engines produce their power at high
rpm—typically well above the optimum
for propeller efficiency. Therefore, most
glow models (200 mph stuff excepted) run
at suboptimal rpm and at considerably less
power than the motor is capable of
producing.
Also, since electric motors tend—in
the case of outrunners or geared types—to
deliver power at a more sensible rpm into
a bigger propeller, the electric power to
match an “hp glow” may be less than 300
watts.
With these caveats, this rule of thumb
has considerable merit if you accept that
an input of approximately 2 kilowatts per
cu. in. is a decent enough guide, which
places a .40 glow at roughly 800 watts
input. The other way is to use the watts/
pound formula and pick a propeller whose
pitch speed (there is a convenient
calculator online) loads the motor to its
rated current draw and is two-and-a-half
to three times the stall speed.
If you want sporty performance, 75-
100 watts per pound is a decent target. I
have found that a typical 5-pound glow
model running at 800 watts is sporty
indeed.
Lead Length Between Motor and ESC
and Battery and ESC: Paul Yee Patrick
(Castle Creations) wrote:
“On the HV controllers especially, the
battery-ESC length is the critical length.
You should not extend the wires more
than a total length of greater than 12
inches without additional capacitors.”
On the motor side, length is less
critical; 18 inches is fine.
“You must keep battery wires (to ESC)
as short as practical,” according to
AstroFlight. “Short means 1 foot or less.
Brushed or brushless makes no
difference.”
From ESC to motor, wire inductance
will not damage your motor, nor will you
be able to detect any effect, even with 100
feet of wire.
Modeling Groups: Judging from the Emails
I get and what I read on various
Internet modeling forums, it appears that
modelers who use computers reflect the
general modeling population. They have
the same questions, the same concerns,
and the same opinions. So what are online
modelers deliberating on or debating?
The thread that comes through is that
there are two distinct groups of modelers,
one of which I call the “What’s in it for
me?” crowd. RC is just “there,” as are
VCRs, television, and Monday Night
Football—theirs for the taking without a
clue about what is required to make it
happen.
The other group has a broader, longer
range of thinking and philosophy that
tends to support more organized modeling
activities, even though they are at violent
odds at times with how the organizations
are approaching the complex subject of
tending to the needs of the modeling
fraternity. If one can keep his or her
perspective, this makes for great
discussions.
That’s it for this month. Support your US
Postal Service and write to me (send an
SASE if you want a personalized answer)
at The Battery Clinic, 12219 NW 9th Ln.,
Newberry FL 32669. E-mail is faster. MA
Sources:
Gene A. Morse
[email protected]
NoBS Batteries
(631) 610-5169
[email protected]
www.hangtimes.com/nobsbatteries.html
Propeller pitch speed calculator
www.rcpro.org/rccalc/PitchSpeed.aspx
Contact
AMA’s Supply & Service Department
for your Product Guide needs
Call (765) 287-1256, extension 212, or visit the AMA Web site at
www.modelaircraft.org. Click on “Shop AMA” to browse the
catalog for the newest merchandise and the best deals on closeout items.
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