Bob Aberle
F r e q u e n t l y A s k e d Q u e s t i o n s
E-mail: [email protected]
FMA Direct Cell Detect, Low Voltage Cutoff Device prevents
discharging Li-Poly batteries below 2.8 volts per cell.
Not seen in this photo, two tiny switches on FMA Direct device
let you select auto low-voltage cutoff or custom cutoff.
Tom Hunt uses heat from his van’s exhaust pipe to eliminate the
warp from the wing of Bob’s Radical RC Mini-Stick.
THIS IS THE 12th monthly column in which you write in or Email
your questions, and I try to give you the best possible answers.
Each inquiry is given a sequential number for identification
purposes.
Because publication space is limited, part of each month’s
installment will appear here, and the columns in their entirety are
posted on the AMA Web site at www.modelaircraft.org/
mag/faq/index.asp. There you can access questions by subject matter
or category. This is to help you retrieve data for particular subjects.
When you call up a question, it reads “Answer ... ” at the end.
Double-click on that word, and the answer, along with any related
photos, will be displayed.
Let’s start!
Q96: “I’ve read a lot about the fact that the new Li-Poly battery
cells should not be discharged below 2.8 to 3.0 volts. Failure to
observe that caution can greatly reduce the life of these cells. I know
most new ESCs can either be selected for the proper cutoff or better
yet will automatically set themselves to the proper cutoff voltage.
“My problem is that I have an older-designed ESC with a fixed
cutoff of 5 volts that was fine for my Ni-Cd and NiMH packs, but
certainly not for Li-Poly batteries. Is there any add-on device I can
buy that will provide the proper cutoff and still allow me to use my
older ESCs?”
A96: There are several such devices on the market, and they range
in price from roughly $20 to $25. I recently received one such
product from FMA Direct called the Automatic Cell Detect, Low
Voltage Cutoff Device—part AVC1AIR.
This add-on enables proper low-voltage cutoff for Li-Poly, Ni-
Cd, and NiMH battery packs when used with older-style ESCs that
don’t provide the proper cutoff. This device is extremely small and
weighs only 0.11 ounce, so it can easily be installed in even parking
Bob reviewed the Hobby Lobby Bonnie 20 advanced ARF electricpowered
trainer for AMA’s Sport Aviator online magazine.
Some Kokam Li-Poly battery packs that Bob retrofitted into the
Bonnie 20 as part of a Sport Aviator follow-up article.
Basic AA-size Ni-Cd or NiMH cells can vary from 600 to 2200
mAh capacity at roughly the same size and weight.
lot-size models with no real weight penalty.
Installation is easy. The servo cable exiting your ESC is plugged
into the connector located on one end of the device. The cable
exiting the device plugs into the throttle port on your RC receiver.
There is one additional wire that must be “spliced into” the positive
(+) battery lead wire as it exits the ESC. Installation instructions are
extremely detailed.
Once installation is complete, you choose from two modes of
operation, the first of which provides automatic cutoff based on a
sampling of the particular battery pack you employ. The second
mode is a custom cutoff, in which you establish your own voltagecutoff
point. Once it is determined, that level (of your choice)
remains in the device’s memory until you change it.
You can find out more about this product at: www.fma
direct.com. In the “Search” option, type in “AVC1AIR” and then
click on the product name.
A similar product is available from Diversity Model Aircraft Inc.
in San Diego, California, called the Li-Saver. It sells for $24.95. You
can learn more about this device at www.flydma.com/fly
dmahome.asp.
No matter which product you choose, the addition of this kind of
device will guarantee that your Li-Poly batteries are not discharged
to less than the minimum recommended 2.8 volts per cell.
Q97: “I have a few questions concerning ‘3-D’ type model aircraft.
Like what is the difference between a ‘3-D’ airplane and a fun-fly
type? Where can I get plans or kits for ‘3-D’ type airplanes? Where
can I find a description of ‘3-D’ type maneuvers?”
A97: Using the term “3-D” to describe a type of model aircraft
began a few years ago when a new style of maneuvering was
developed. 3-D airplanes are capable of hovering and doing Torque
Rolls, Harriers, Rollers, etc.
These models must have a power-to-weight ratio of at least 2:1
and extremely quick throttle response to be able to correct for minor
deviations while hovering or flying behind the power curve. The
term “3-D” implies glow or gas power, and the term “E-3-D”
describes the equivalent aircraft using electric power.
Several publications are now covering 3-D and E-3-D. Quiet
Flyer magazine publisher Wil Byers has introduced a new magazine
called 3-D Flyer, which specializes in all aspects of this type of
aircraft. You can find an advertisement and special offer for this
publication in the MA Special Issue 2004 on page 158.
Popular modeling author Dave Baron writes the new monthly
“Freestyle” column for Fly RC magazine. He has written some of
the best articles about the physics and dynamics of flying behind the
power curve.
These references should at least provide you with a start!
Q98: “I recently had a situation where my RC pilot instructor told
me at the flying field that I had a warp in my wing and that I should
remove it before he would allow me to fly. That was the end of my
flying for that day, before I even started.
“I learned my lesson and will be more observant in the future.
But looking back, is there any way I could have saved my day of
flying?”
A98: I have a suggestion, but you have to be careful about how you
go about it. I recently had a similar problem while attempting to fly
a new model to obtain some flight shots for a review. But my flying
partner Tom Hunt (founder and director of the annual Northeast
Electric Aircraft Technology Fair) always has many practical ideas
up his sleeve.
Before I could say anything, he started his minivan’s engine. The
next thing I knew, he was kneeling by the rear of the van, holding
my model’s wing at a particular angle and
letting the hot engine exhaust soften the
covering material.
You don’t get a great deal of heat this
way, but it is enough to get the job done for
at least one flying session. But remember not
to get too close to that exhaust pipe, for
obvious reasons.
Q99: “I am in the process of finishing a
twin-engine model aircraft and plan on
employing up to 10 Futaba S3003s servos.
Do you think a standard four-cell, 4.8-volt,
600 mAh receiver pack is okay for this?
“Futaba sells four-cell packs, but with
higher capacities (both 1000 and 1500 mAh),
which I could upgrade to. They also sell a
five-cell, 6.0-volt, 600 mAh pack. Would
going to five cells be better for my particular
application?”
A99: I’m not sure what the average current
draw is on the Futaba S3003s servos. With
the exception of the new digital servos (that
draw a lot of current), most receivers and
four servos will average 50 mA at idle.
When you pulse (move) one servo
rapidly, you can easily draw 300 mA. If you
pulse or operate two servos at one time, you
can get current levels up to 500-600 mA.
When using 10 servos, the idle alone could
exceed 1000 mA. You won’t realistically be
operating all of these servos at one time.
However, you might still see loads upward
of 1000 mA (1.0 amp).
That being the case, I feel that the 600
mAh pack is marginal! You would probably
be wise to go to the Futaba 1500 mAh
battery pack. I suggest that you buy a fourcell
pack consisting of the newer 2000-2300
mAh NiMH cells. They are still AA size and
weigh almost the same as a 600 mAh pack.
If you do go that route, make sure you
charge a 2000 mAh pack overnight at 200
mA. Don’t play games using an ordinary
RC-system charger, leaving the pack on
charge for three days instead of overnight.
The battery chemistry won’t be happy, and
the result could be that your 2000 mAh pack
gives you much less capacity. Buy that Ace
DDVC charger that I always recommend for
charging these larger-capacity packs at the
proper overnight current level.
Regarding the question of four- versus
five-cell receiver packs, using higher
voltage, by itself, does not improve your
battery capacity. That extra cell allows your
servos to move faster and have a little more
output torque. Some people like this faster
servo response time.
But on the less-expensive servos,
sometimes more is not better. The servos
may move faster, but they might overshoot
their intended position, causing erratic flying
because of the higher transit speed.
It is a compromise! I’ve been flying
digital proportional control since 1968 and
have never used a five-cell (6.0-volt)
airborne battery pack.
Q100: “Back in March (2004) you
mentioned a Sport Aviator review article
(this is the AMA’s new online magazine) of
the Hobbico SuperStar EP that you were
going to follow up with an application
article describing the new FMA/Kokam
2000 mAh HD Li-Poly batteries.
“I have a similar application for those
batteries and waited to see your article, but it
never appeared. What is the status of that
article?”
A100: The SuperStar EP is a three-channel,
tail-dragger-type trainer. Sport Aviator
editor Frank Granelli decided that it would
be wise to go to the next step and move up
to an advanced trainer with ailerons, fourchannel
function control, a tricycle gear
with nose-wheel steering, and a new AXI
brushless outrunner motor. He selected the
popular Hobby Lobby Bonnie 20 ARF.
You can find a detailed review at
www.masport
aviator.com/ah.asp?CatID=1&ID=39.
The next step in this process was to
retrofit the new Kokam 2000 mAh (15Cand
20C-load capable) Li-Poly batteries,
from FMA Direct, into the Bonnie 20. You
can find a detailed article about the Li-Poly
application at www.masportaviator.com/
ah.asp?CatID=2&ID=43. I believe that it
will provide you with all the details you
need.
We keep adding more reviews and
application articles to this new onlinemagazine
format. Because it is essentially
an electronic media, we are not limited to
pages as we are when paper is involved.
The result is more in-depth reporting. Sport
Aviator is available to the general public;
no identification numbers or passwords are
necessary.
That’s a wrap for this month. Please keep
writing in with your questions. Are you
having trouble understanding something or
need help with certain building techniques?
You just saw a new product advertised and
was wondering about its application? If you
have the questions, my team of experts and I
should be able to provide you with answers.
Please remember to look at the
Frequently Asked Questions section of the
MA Web site; only half of my monthly
output is published here. MA
Edition: Model Aviation - 2005/03
Page Numbers: 65,66,68
Edition: Model Aviation - 2005/03
Page Numbers: 65,66,68
Bob Aberle
F r e q u e n t l y A s k e d Q u e s t i o n s
E-mail: [email protected]
FMA Direct Cell Detect, Low Voltage Cutoff Device prevents
discharging Li-Poly batteries below 2.8 volts per cell.
Not seen in this photo, two tiny switches on FMA Direct device
let you select auto low-voltage cutoff or custom cutoff.
Tom Hunt uses heat from his van’s exhaust pipe to eliminate the
warp from the wing of Bob’s Radical RC Mini-Stick.
THIS IS THE 12th monthly column in which you write in or Email
your questions, and I try to give you the best possible answers.
Each inquiry is given a sequential number for identification
purposes.
Because publication space is limited, part of each month’s
installment will appear here, and the columns in their entirety are
posted on the AMA Web site at www.modelaircraft.org/
mag/faq/index.asp. There you can access questions by subject matter
or category. This is to help you retrieve data for particular subjects.
When you call up a question, it reads “Answer ... ” at the end.
Double-click on that word, and the answer, along with any related
photos, will be displayed.
Let’s start!
Q96: “I’ve read a lot about the fact that the new Li-Poly battery
cells should not be discharged below 2.8 to 3.0 volts. Failure to
observe that caution can greatly reduce the life of these cells. I know
most new ESCs can either be selected for the proper cutoff or better
yet will automatically set themselves to the proper cutoff voltage.
“My problem is that I have an older-designed ESC with a fixed
cutoff of 5 volts that was fine for my Ni-Cd and NiMH packs, but
certainly not for Li-Poly batteries. Is there any add-on device I can
buy that will provide the proper cutoff and still allow me to use my
older ESCs?”
A96: There are several such devices on the market, and they range
in price from roughly $20 to $25. I recently received one such
product from FMA Direct called the Automatic Cell Detect, Low
Voltage Cutoff Device—part AVC1AIR.
This add-on enables proper low-voltage cutoff for Li-Poly, Ni-
Cd, and NiMH battery packs when used with older-style ESCs that
don’t provide the proper cutoff. This device is extremely small and
weighs only 0.11 ounce, so it can easily be installed in even parking
Bob reviewed the Hobby Lobby Bonnie 20 advanced ARF electricpowered
trainer for AMA’s Sport Aviator online magazine.
Some Kokam Li-Poly battery packs that Bob retrofitted into the
Bonnie 20 as part of a Sport Aviator follow-up article.
Basic AA-size Ni-Cd or NiMH cells can vary from 600 to 2200
mAh capacity at roughly the same size and weight.
lot-size models with no real weight penalty.
Installation is easy. The servo cable exiting your ESC is plugged
into the connector located on one end of the device. The cable
exiting the device plugs into the throttle port on your RC receiver.
There is one additional wire that must be “spliced into” the positive
(+) battery lead wire as it exits the ESC. Installation instructions are
extremely detailed.
Once installation is complete, you choose from two modes of
operation, the first of which provides automatic cutoff based on a
sampling of the particular battery pack you employ. The second
mode is a custom cutoff, in which you establish your own voltagecutoff
point. Once it is determined, that level (of your choice)
remains in the device’s memory until you change it.
You can find out more about this product at: www.fma
direct.com. In the “Search” option, type in “AVC1AIR” and then
click on the product name.
A similar product is available from Diversity Model Aircraft Inc.
in San Diego, California, called the Li-Saver. It sells for $24.95. You
can learn more about this device at www.flydma.com/fly
dmahome.asp.
No matter which product you choose, the addition of this kind of
device will guarantee that your Li-Poly batteries are not discharged
to less than the minimum recommended 2.8 volts per cell.
Q97: “I have a few questions concerning ‘3-D’ type model aircraft.
Like what is the difference between a ‘3-D’ airplane and a fun-fly
type? Where can I get plans or kits for ‘3-D’ type airplanes? Where
can I find a description of ‘3-D’ type maneuvers?”
A97: Using the term “3-D” to describe a type of model aircraft
began a few years ago when a new style of maneuvering was
developed. 3-D airplanes are capable of hovering and doing Torque
Rolls, Harriers, Rollers, etc.
These models must have a power-to-weight ratio of at least 2:1
and extremely quick throttle response to be able to correct for minor
deviations while hovering or flying behind the power curve. The
term “3-D” implies glow or gas power, and the term “E-3-D”
describes the equivalent aircraft using electric power.
Several publications are now covering 3-D and E-3-D. Quiet
Flyer magazine publisher Wil Byers has introduced a new magazine
called 3-D Flyer, which specializes in all aspects of this type of
aircraft. You can find an advertisement and special offer for this
publication in the MA Special Issue 2004 on page 158.
Popular modeling author Dave Baron writes the new monthly
“Freestyle” column for Fly RC magazine. He has written some of
the best articles about the physics and dynamics of flying behind the
power curve.
These references should at least provide you with a start!
Q98: “I recently had a situation where my RC pilot instructor told
me at the flying field that I had a warp in my wing and that I should
remove it before he would allow me to fly. That was the end of my
flying for that day, before I even started.
“I learned my lesson and will be more observant in the future.
But looking back, is there any way I could have saved my day of
flying?”
A98: I have a suggestion, but you have to be careful about how you
go about it. I recently had a similar problem while attempting to fly
a new model to obtain some flight shots for a review. But my flying
partner Tom Hunt (founder and director of the annual Northeast
Electric Aircraft Technology Fair) always has many practical ideas
up his sleeve.
Before I could say anything, he started his minivan’s engine. The
next thing I knew, he was kneeling by the rear of the van, holding
my model’s wing at a particular angle and
letting the hot engine exhaust soften the
covering material.
You don’t get a great deal of heat this
way, but it is enough to get the job done for
at least one flying session. But remember not
to get too close to that exhaust pipe, for
obvious reasons.
Q99: “I am in the process of finishing a
twin-engine model aircraft and plan on
employing up to 10 Futaba S3003s servos.
Do you think a standard four-cell, 4.8-volt,
600 mAh receiver pack is okay for this?
“Futaba sells four-cell packs, but with
higher capacities (both 1000 and 1500 mAh),
which I could upgrade to. They also sell a
five-cell, 6.0-volt, 600 mAh pack. Would
going to five cells be better for my particular
application?”
A99: I’m not sure what the average current
draw is on the Futaba S3003s servos. With
the exception of the new digital servos (that
draw a lot of current), most receivers and
four servos will average 50 mA at idle.
When you pulse (move) one servo
rapidly, you can easily draw 300 mA. If you
pulse or operate two servos at one time, you
can get current levels up to 500-600 mA.
When using 10 servos, the idle alone could
exceed 1000 mA. You won’t realistically be
operating all of these servos at one time.
However, you might still see loads upward
of 1000 mA (1.0 amp).
That being the case, I feel that the 600
mAh pack is marginal! You would probably
be wise to go to the Futaba 1500 mAh
battery pack. I suggest that you buy a fourcell
pack consisting of the newer 2000-2300
mAh NiMH cells. They are still AA size and
weigh almost the same as a 600 mAh pack.
If you do go that route, make sure you
charge a 2000 mAh pack overnight at 200
mA. Don’t play games using an ordinary
RC-system charger, leaving the pack on
charge for three days instead of overnight.
The battery chemistry won’t be happy, and
the result could be that your 2000 mAh pack
gives you much less capacity. Buy that Ace
DDVC charger that I always recommend for
charging these larger-capacity packs at the
proper overnight current level.
Regarding the question of four- versus
five-cell receiver packs, using higher
voltage, by itself, does not improve your
battery capacity. That extra cell allows your
servos to move faster and have a little more
output torque. Some people like this faster
servo response time.
But on the less-expensive servos,
sometimes more is not better. The servos
may move faster, but they might overshoot
their intended position, causing erratic flying
because of the higher transit speed.
It is a compromise! I’ve been flying
digital proportional control since 1968 and
have never used a five-cell (6.0-volt)
airborne battery pack.
Q100: “Back in March (2004) you
mentioned a Sport Aviator review article
(this is the AMA’s new online magazine) of
the Hobbico SuperStar EP that you were
going to follow up with an application
article describing the new FMA/Kokam
2000 mAh HD Li-Poly batteries.
“I have a similar application for those
batteries and waited to see your article, but it
never appeared. What is the status of that
article?”
A100: The SuperStar EP is a three-channel,
tail-dragger-type trainer. Sport Aviator
editor Frank Granelli decided that it would
be wise to go to the next step and move up
to an advanced trainer with ailerons, fourchannel
function control, a tricycle gear
with nose-wheel steering, and a new AXI
brushless outrunner motor. He selected the
popular Hobby Lobby Bonnie 20 ARF.
You can find a detailed review at
www.masport
aviator.com/ah.asp?CatID=1&ID=39.
The next step in this process was to
retrofit the new Kokam 2000 mAh (15Cand
20C-load capable) Li-Poly batteries,
from FMA Direct, into the Bonnie 20. You
can find a detailed article about the Li-Poly
application at www.masportaviator.com/
ah.asp?CatID=2&ID=43. I believe that it
will provide you with all the details you
need.
We keep adding more reviews and
application articles to this new onlinemagazine
format. Because it is essentially
an electronic media, we are not limited to
pages as we are when paper is involved.
The result is more in-depth reporting. Sport
Aviator is available to the general public;
no identification numbers or passwords are
necessary.
That’s a wrap for this month. Please keep
writing in with your questions. Are you
having trouble understanding something or
need help with certain building techniques?
You just saw a new product advertised and
was wondering about its application? If you
have the questions, my team of experts and I
should be able to provide you with answers.
Please remember to look at the
Frequently Asked Questions section of the
MA Web site; only half of my monthly
output is published here. MA
Edition: Model Aviation - 2005/03
Page Numbers: 65,66,68
Bob Aberle
F r e q u e n t l y A s k e d Q u e s t i o n s
E-mail: [email protected]
FMA Direct Cell Detect, Low Voltage Cutoff Device prevents
discharging Li-Poly batteries below 2.8 volts per cell.
Not seen in this photo, two tiny switches on FMA Direct device
let you select auto low-voltage cutoff or custom cutoff.
Tom Hunt uses heat from his van’s exhaust pipe to eliminate the
warp from the wing of Bob’s Radical RC Mini-Stick.
THIS IS THE 12th monthly column in which you write in or Email
your questions, and I try to give you the best possible answers.
Each inquiry is given a sequential number for identification
purposes.
Because publication space is limited, part of each month’s
installment will appear here, and the columns in their entirety are
posted on the AMA Web site at www.modelaircraft.org/
mag/faq/index.asp. There you can access questions by subject matter
or category. This is to help you retrieve data for particular subjects.
When you call up a question, it reads “Answer ... ” at the end.
Double-click on that word, and the answer, along with any related
photos, will be displayed.
Let’s start!
Q96: “I’ve read a lot about the fact that the new Li-Poly battery
cells should not be discharged below 2.8 to 3.0 volts. Failure to
observe that caution can greatly reduce the life of these cells. I know
most new ESCs can either be selected for the proper cutoff or better
yet will automatically set themselves to the proper cutoff voltage.
“My problem is that I have an older-designed ESC with a fixed
cutoff of 5 volts that was fine for my Ni-Cd and NiMH packs, but
certainly not for Li-Poly batteries. Is there any add-on device I can
buy that will provide the proper cutoff and still allow me to use my
older ESCs?”
A96: There are several such devices on the market, and they range
in price from roughly $20 to $25. I recently received one such
product from FMA Direct called the Automatic Cell Detect, Low
Voltage Cutoff Device—part AVC1AIR.
This add-on enables proper low-voltage cutoff for Li-Poly, Ni-
Cd, and NiMH battery packs when used with older-style ESCs that
don’t provide the proper cutoff. This device is extremely small and
weighs only 0.11 ounce, so it can easily be installed in even parking
Bob reviewed the Hobby Lobby Bonnie 20 advanced ARF electricpowered
trainer for AMA’s Sport Aviator online magazine.
Some Kokam Li-Poly battery packs that Bob retrofitted into the
Bonnie 20 as part of a Sport Aviator follow-up article.
Basic AA-size Ni-Cd or NiMH cells can vary from 600 to 2200
mAh capacity at roughly the same size and weight.
lot-size models with no real weight penalty.
Installation is easy. The servo cable exiting your ESC is plugged
into the connector located on one end of the device. The cable
exiting the device plugs into the throttle port on your RC receiver.
There is one additional wire that must be “spliced into” the positive
(+) battery lead wire as it exits the ESC. Installation instructions are
extremely detailed.
Once installation is complete, you choose from two modes of
operation, the first of which provides automatic cutoff based on a
sampling of the particular battery pack you employ. The second
mode is a custom cutoff, in which you establish your own voltagecutoff
point. Once it is determined, that level (of your choice)
remains in the device’s memory until you change it.
You can find out more about this product at: www.fma
direct.com. In the “Search” option, type in “AVC1AIR” and then
click on the product name.
A similar product is available from Diversity Model Aircraft Inc.
in San Diego, California, called the Li-Saver. It sells for $24.95. You
can learn more about this device at www.flydma.com/fly
dmahome.asp.
No matter which product you choose, the addition of this kind of
device will guarantee that your Li-Poly batteries are not discharged
to less than the minimum recommended 2.8 volts per cell.
Q97: “I have a few questions concerning ‘3-D’ type model aircraft.
Like what is the difference between a ‘3-D’ airplane and a fun-fly
type? Where can I get plans or kits for ‘3-D’ type airplanes? Where
can I find a description of ‘3-D’ type maneuvers?”
A97: Using the term “3-D” to describe a type of model aircraft
began a few years ago when a new style of maneuvering was
developed. 3-D airplanes are capable of hovering and doing Torque
Rolls, Harriers, Rollers, etc.
These models must have a power-to-weight ratio of at least 2:1
and extremely quick throttle response to be able to correct for minor
deviations while hovering or flying behind the power curve. The
term “3-D” implies glow or gas power, and the term “E-3-D”
describes the equivalent aircraft using electric power.
Several publications are now covering 3-D and E-3-D. Quiet
Flyer magazine publisher Wil Byers has introduced a new magazine
called 3-D Flyer, which specializes in all aspects of this type of
aircraft. You can find an advertisement and special offer for this
publication in the MA Special Issue 2004 on page 158.
Popular modeling author Dave Baron writes the new monthly
“Freestyle” column for Fly RC magazine. He has written some of
the best articles about the physics and dynamics of flying behind the
power curve.
These references should at least provide you with a start!
Q98: “I recently had a situation where my RC pilot instructor told
me at the flying field that I had a warp in my wing and that I should
remove it before he would allow me to fly. That was the end of my
flying for that day, before I even started.
“I learned my lesson and will be more observant in the future.
But looking back, is there any way I could have saved my day of
flying?”
A98: I have a suggestion, but you have to be careful about how you
go about it. I recently had a similar problem while attempting to fly
a new model to obtain some flight shots for a review. But my flying
partner Tom Hunt (founder and director of the annual Northeast
Electric Aircraft Technology Fair) always has many practical ideas
up his sleeve.
Before I could say anything, he started his minivan’s engine. The
next thing I knew, he was kneeling by the rear of the van, holding
my model’s wing at a particular angle and
letting the hot engine exhaust soften the
covering material.
You don’t get a great deal of heat this
way, but it is enough to get the job done for
at least one flying session. But remember not
to get too close to that exhaust pipe, for
obvious reasons.
Q99: “I am in the process of finishing a
twin-engine model aircraft and plan on
employing up to 10 Futaba S3003s servos.
Do you think a standard four-cell, 4.8-volt,
600 mAh receiver pack is okay for this?
“Futaba sells four-cell packs, but with
higher capacities (both 1000 and 1500 mAh),
which I could upgrade to. They also sell a
five-cell, 6.0-volt, 600 mAh pack. Would
going to five cells be better for my particular
application?”
A99: I’m not sure what the average current
draw is on the Futaba S3003s servos. With
the exception of the new digital servos (that
draw a lot of current), most receivers and
four servos will average 50 mA at idle.
When you pulse (move) one servo
rapidly, you can easily draw 300 mA. If you
pulse or operate two servos at one time, you
can get current levels up to 500-600 mA.
When using 10 servos, the idle alone could
exceed 1000 mA. You won’t realistically be
operating all of these servos at one time.
However, you might still see loads upward
of 1000 mA (1.0 amp).
That being the case, I feel that the 600
mAh pack is marginal! You would probably
be wise to go to the Futaba 1500 mAh
battery pack. I suggest that you buy a fourcell
pack consisting of the newer 2000-2300
mAh NiMH cells. They are still AA size and
weigh almost the same as a 600 mAh pack.
If you do go that route, make sure you
charge a 2000 mAh pack overnight at 200
mA. Don’t play games using an ordinary
RC-system charger, leaving the pack on
charge for three days instead of overnight.
The battery chemistry won’t be happy, and
the result could be that your 2000 mAh pack
gives you much less capacity. Buy that Ace
DDVC charger that I always recommend for
charging these larger-capacity packs at the
proper overnight current level.
Regarding the question of four- versus
five-cell receiver packs, using higher
voltage, by itself, does not improve your
battery capacity. That extra cell allows your
servos to move faster and have a little more
output torque. Some people like this faster
servo response time.
But on the less-expensive servos,
sometimes more is not better. The servos
may move faster, but they might overshoot
their intended position, causing erratic flying
because of the higher transit speed.
It is a compromise! I’ve been flying
digital proportional control since 1968 and
have never used a five-cell (6.0-volt)
airborne battery pack.
Q100: “Back in March (2004) you
mentioned a Sport Aviator review article
(this is the AMA’s new online magazine) of
the Hobbico SuperStar EP that you were
going to follow up with an application
article describing the new FMA/Kokam
2000 mAh HD Li-Poly batteries.
“I have a similar application for those
batteries and waited to see your article, but it
never appeared. What is the status of that
article?”
A100: The SuperStar EP is a three-channel,
tail-dragger-type trainer. Sport Aviator
editor Frank Granelli decided that it would
be wise to go to the next step and move up
to an advanced trainer with ailerons, fourchannel
function control, a tricycle gear
with nose-wheel steering, and a new AXI
brushless outrunner motor. He selected the
popular Hobby Lobby Bonnie 20 ARF.
You can find a detailed review at
www.masport
aviator.com/ah.asp?CatID=1&ID=39.
The next step in this process was to
retrofit the new Kokam 2000 mAh (15Cand
20C-load capable) Li-Poly batteries,
from FMA Direct, into the Bonnie 20. You
can find a detailed article about the Li-Poly
application at www.masportaviator.com/
ah.asp?CatID=2&ID=43. I believe that it
will provide you with all the details you
need.
We keep adding more reviews and
application articles to this new onlinemagazine
format. Because it is essentially
an electronic media, we are not limited to
pages as we are when paper is involved.
The result is more in-depth reporting. Sport
Aviator is available to the general public;
no identification numbers or passwords are
necessary.
That’s a wrap for this month. Please keep
writing in with your questions. Are you
having trouble understanding something or
need help with certain building techniques?
You just saw a new product advertised and
was wondering about its application? If you
have the questions, my team of experts and I
should be able to provide you with answers.
Please remember to look at the
Frequently Asked Questions section of the
MA Web site; only half of my monthly
output is published here. MA