Safety Comes First - 2008/01

92 MODEL AVIATION
DO YOU
remember the
electrical charging
station I described
in a recent column?
Dave Sweeney
designed it, and
Willie Gardner built
it with a solar panel
hooked to a storage
battery and shelves
attached to a metal
building so that
flight packs are in a
safe and visible area
during recharge.
I neglected to
mention the topnotch
work Willie
and Dave did on
this project; in fact,
I didn’t print their
names at all.
Unfortunately space
is limited, or I
would have let them see their names in MA this month.
Dave Sweeney and Willie Gardner deserve proper credit,
especially since their invention is so popular that they are planning
to expand the electrical storage system to provide more charging
power on cloudy days.
E-mail has rolled in lately to tell me what a goof I made when I
mentioned prescription eyeglasses but didn’t say that such glasses
alone don’t provide full protection when using power tools. More than
Safety Comes First Dave Gee | [email protected]
Solar-powered battery storage and charging station
Also included in this column:
• Proper eye protection for
power-tool use
• Why impound a Spektrum
radio?
• Shattering info about broken
cutoff wheels
• Using low-rated switches in
high-power circuits
• This month’s photos
• Review of the fun CL system
by P3 Models
Nikki Robichau is learning to fly her RC helicopter with her dad’s
help. Kids have quick reflexes and can develop RC flying skills
faster than adults can.
Mark Miller makes sure other fliers can locate and identify his
models by putting photos on his frequency pins.
P3 Models’ Revolution allows a CL pilot to fly from outside the
circle. This column contains a review of the system.
01sig3.QXD 11/19/07 3:08 PM Page 92
one eye doctor reminded me that particles
can easily ricochet around standard glasses
and that we need to use protection that
fully covers the eyes. I should have made
that clear!
There used to be little plastic end pieces
that would clip onto glasses and provide
side coverage. You could see them used at
any machine shop, but lately I’ve been
unable to find such a product. My glasses
are oversized and leave no gaps at my nose
or cheek, but the sides are still wide open.
If you know of a source for the clip-on
side pieces I described, please E-mail me
or send a note to Box 7081, Van Nuys CA
91409. You can also use these addresses to
let me know how I goofed up this month.
Walt Keating thought he had me on a
transmitter impound story, and he E-mailed
his thoughts.
“In your story about a recent fun-fly,
you stated that even the new Spektrum
system users understood that their radios
belonged on the impound table. May I ask
why?
“I recently attended Top Gun here in
Florida and I can assure you that no
Spektrum user was subjected to impound
nor was there any ‘understanding’ relative
to that issue. Spektrum radios do not
require impound because they are not
subject to interference like older systems.”
Walt, I realize that interference is a
nonissue with the new radios. But we are
in a transition period, and that meet was
many months ago when some fliers had
still never even seen a Spektrum system.
They impounded the radios for
consistency, to make sure some new guy
didn’t see a nonimpounded transmitter in
use in the pits and figure he could do the
same with his 72 MHz system.
It probably won’t be long before this
precaution is no longer needed, but at the
time it was a good idea. You have to figure
things by imagining what the dumbest guy
on the field will do. (When I am not
present they pick a new dumbest guy.)
Another omission of mine was corrected
by Jeff Hails, who wrote:
94 MODEL AVIATION
“I was glad to see some discussion of
safety with cutoff wheels. I grew up building
slot car chassis and cutoff wheels were the tool
of choice for cutting spring steel and brass
sheet, or piano wire. The first lesson I learned
was never, ever put your body in the plane of
the wheel.”
Jeff is absolutely right, and I should have
covered that point. Visualizing an imaginary
extension of the cutting disk is hard for some,
but that is where things will fly if the wheel
shatters.
The same is true of propellers. The “plane”
of the spinning blades is a danger zone, and it
is a good idea to minimize our exposure to this
area.
It helps me to picture the vertical lines that
were sometimes painted on the fuselage of
bombers to warn ground crews about the
presence of a spinning propeller. The lines
mark an extension of the propeller disk as it
meets the airplane.
This reminder keeps my mind on “what
might happen if ... ” and I try to position my
work such that the edge of the cutting disk
does not line up with my body parts.
I received an informative message from
Camille Goudeseune, who is a columnist for
Quiet Flyer magazine. He wrote:
“You mentioned that arming switches can
be difficult for high-current electric motors.
This is not necessarily true. You can use a
switch rated for low current at much higher
currents—as long as you don’t move the
switch when high current would flow across it,
arcing the contacts.
“So you don’t need a heavy 50-amp
industrial knife-blade switch on board. Just
zero the throttle before you arm or disarm.”
He is right, but I am the wrong guy to have
such a setup since my policy is to commit
whatever goofs are possible. If you are more
organized and disciplined than I am, Camille’s
information could save you some onboard
weight and provide a little performance boost.
Camille also complimented this column’s
“density.” I’m pretty sure he meant that I cram
a lot of stuff in each month and was not
making a comment about my mental prowess
(or lack thereof). Such flattery!
01sig3.QXD 11/19/07 3:09 PM Page 94
Look at the picture showing frequency
pins with photos on them. Mark Miller
made these, and he assured me that it is not
a new idea. It was new to me, and I think
Mark is clever for making it easy for other
pilots to identify which model is on a given
channel. (The little photos don’t do justice
to his beautiful models!)
The other photo shows Nikki Robichau
with her electric helicopter. Note the
training skids that she uses while her dad
teaches her to fly. Nikki flies a Blade CX2,
which uses a Spektrum-equipped E-flite
radio.
She thought it was funny that I
photographed her instead of the other
helicopter pilots at the field. Model
aviation is a relaxing hobby that brings
generations together, and it makes them
shout “pull up!” at each other.
Many AMA members came into modeling
via RC and have never flown a CL model.
What a shame! The distinctive “vroom,
vroom” sound as a model races around the
circle reminds me of the days when gas CL
was the big thing.
At the last AMA Convention I visited
the P3 Models booth and saw its
Revolution system: a setup that allows you
to fly CL from outside the circle. I was
interested in this product, and when the
chance came to review it I eagerly
volunteered. It is a great item and a fun
way to fly a model.
The Revolution is basically a sturdy
swiveling linkage that allows a pilot to fly
a CL aircraft while standing still, outside
the circle. A number of products through
the years have tried to accomplish this, but
the Revolution impressed me with its solid
engineering and thoughtful design. It really
works as advertised.
The center post has a swiveling head
that takes the pull of the model and
transmits control input from the pilot’s
handle. The parts are ruggedly built, but
you wouldn’t want to leave the Revolution
out in the weather.
Setup is easy enough for even a
columnist to do. P3 Models has a great
video on its Web site that takes you
through the process.
The components break down to fit into a
handy storage box, but the system doesn’t
have to be fully disassembled every time
you take it down. Leaving some of the
parts hooked up saves time and doesn’t
take up much space. A DVD comes in the
package and is available separately.
One person can start and fly the model
without help or a stooge (not that I
recommend operating a gas model alone at
the field!), and the Revolution is especially
good for disabled modelers who might not
be able to turn ’round and ’round with a
conventional CL aircraft.
Those who get too dizzy to fly CL
would also be excellent candidates for the
Revolution. (I’ve never gotten dizzy flying
CL, even on very short lines, because I was
taught to concentrate on the model rather
than on the passing scenery.) Student pilots
can stand still with an instructor and not
worry about the airplane’s weight as they
fly.
The swiveling control head allows for
level flight, climbs and dives, and semi-
Wingovers. You can’t do the CL
Aerobatics (Stunt) pattern with the
Revolution, but I couldn’t do the Stunt
pattern even if I were channeling the spirit
of Jim Walker.
There is no whipping possible, and the
“feel” of being connected to the model (a
special benefit of CL flying) is much more
subtle than with conventional CL but still
noticeable.
The standard version of the Revolution
that I tested is designed for a full-size gas
or electric CL model. It needs a grass field
because the center pylon is staked down. I
understand that the company is working on
a smaller version for 1/2A models and
possibly a way to use the system on a
paved circle.
The Revolution’s introductory price is
$299.99, which strikes me as quite a
bargain for such a high-quality unit. MA
Sources:
P3 Models
(800) 515-5951
www.p3models.com
96 MODEL AVIATION
01sig3.QXD 11/19/07 3:09 PM Page 96
Banana plugs that fit into alligator clips is a great idea
January 2008 97
The Battery Clinic Red Scholefield | [email protected]
Also included in this column:
• Don’t smoke your ESC
• New cell tester for Li-Polys
and A123 packs
• VoltMagic upgrade
• Cover that ugly hole where
your glow engine was
The SLK Electronics B1 cell tester.
Modify your own alligator clips to accept banana plugs.
New Cellpro charger with convertible alligator clips.
I’M GLAD TO see that charger
manufacturers have finally figured it out.
Following the lead of Triton 2 and TME’s
Xtrema, FMA Direct is now shipping its
popular Cellpro charger balancer with banana
leads and alligator clips that plug into each
other.
Most serious electric-power fliers have set
up their chargers with banana plugs so they
can easily connect to bench power supplies or
cigarette-lighter plugs modified to accept
banana jacks. The photograph with the
alligator clip shows this simple modification
using a 7/8-inch length of 3/16-inch-diameter
brass tubing and soldering to the inside of the
alligator clip.
The following is not necessarily about
batteries, but it is an interesting discussion
about wattmeters. A reader wrote:
“I smoked my 80 amp ESC this weekend
while running the EDF on the bench. The
vendor says it’s due to my having a
Whattmeter in series when I ran the motor.
The Whattmeter introduces resistance thereby
increasing the ripple beyond what the input
capacitors can handle so it blew up the Power
MOSFETS and most of the power board.
“They recommend that we do not use any
kind of wattmeter to measure power if the
current draw is expected to exceed 25 amps or
so, but instead use a DC clamp on meter like
what you can get at Sears. Not that accurate
but close enough and prevents blowing up
ESC.”
I thought to myself, How could this be? If
it were true, people would be blowing ESCs
all over the place. I’ve used my wattmeter on
a number of different ESCs with no problem.
Nevertheless, consulting the experts wasn’t a
bad idea. Following is a compilation of a
number of conversations with Keith Shaw,
Doug Ingraham (designer of the Whattmeter),
Greg Gimlick, Greg Covey, and Ken Myers.
01sig4.QXD 11/20/07 8:56 AM Page 97
Balancing Ni-Cd/NiMH Vs. Lithium Batteries: There seems to be a bit
of confusion about this. No one ever thought much about balancing
Nickel technology packs. It happened automatically if you used them
with any charger that had a trickle capability after peak charging or you
were using the wall-wart charger that came with your radio system.
Since those are constant-current devices when it comes to charging,
all the cells, if left on trickle, came to their maximum state of charge
because they were getting the same current and could stand some
amount of overcharge.
Lithium systems are different. They are constant-voltage systems,
which means you charge the cells to a specific level and then stop. Each
cell must be brought up to that level to balance the pack. This is where
the problem occurs.
When you are charging them in series as they are always used, the
charger looks for X multiplied by 4.2 volts. So in a 3S pack it is looking
for 12.6 volts. Forget that this pack is labeled 11.1; that is the nominal
voltage.
Suppose that one cell is charged before its neighbors for some
reason. It can be driven to a higher voltage, while the others have yet to
reach 4.2 (the cell’s peak voltage). Going beyond 4.2 volts is
detrimental to cell life. Hence we have to balance each cell individually,
which is what a properly designed balancing charger does.
This should not come as a great shock since large banks of lead-acid
batteries used in emergency power situations go through frequent cellbalancing
procedures for the same reason that Lithium cells require it.
Lead-acid is a constant-voltage system.
SLK Electronics B1: Sid Kauffman has come up with another handy
battery tool: a cell tester/balancer. It was conceived as an economical
cell balancer for M1 (A123Systems) batteries.
My field experience has shown that these cells stay in balance well.
It is normally necessary to check them only periodically. The problem
is that the cell-voltage differences are tiny during charge until almost
full.
If M1 cells are checked at the end of charge, they frequently appear
to be unbalanced when they are not. Conversely, if checked when not
fully charged, they can appear to be balanced when they are not.
The B1 cell tester allows you to measure each cell voltage (one at a
time) using the balancing tap connector and either charge or discharge
each cell. It can also be used to check and balance your Li-Poly cells
one at a time. This device measures cell voltage from 2.8 to 5.8 with a
5.0-millivolt resolution. You can also use it to check your four-cell
receiver packs.
Three pages of detailed operating instructions for the B1 are
provided on the SLK Web site. To learn more about the unit you can
also read the instructions, which are posted on the site in PDF format.
What would you do if your favorite cordless tool died? Don’t despair.
One of my fellow club members had a small Makita drill with the
Doug said:
“Adding the Whattmeter should not be the cause of a problem.
The wattmeter is a minor resistance source. About the same as adding
a length of 13 gauge wire of whatever length the leads are.
“The positive lead is nothing more than a wire with a tap. The
negative lead has a precision non inductive shunt in the line which is
only slightly higher than the equivalent length of wire. The battery
resistance is orders of magnitude greater than the wattmeter.
“In my opinion this was not the cause of the ESC burning up.
There must have been some other contributing factor.
“The addition of much longer leads in the circuit (several
additional feet) would be needed for the inductance to be a problem.
The inductance in the wires between the battery and the ESC while
small can cause the voltage to spike when the MOSFET switches are
turned off in the ESC. The absorption of these spikes are the purpose
of the input capacitor. An increase in current makes this more likely.
Damage to the MOSFETs is cumulative.”
As near as I can recall, the following was second-hand via Greg
Gimlick, I think, from Keith Shaw.
“The other source of high voltage spikes that can’t be controlled so
much by the input capacitor is on the motor
side. These spikes are shunted back into the
battery by the body diodes of the MOSFET.
“The inductance of the motor is huge
(which is especially true of outrunners). I can
almost guarantee that a way to kill a speed
control is to run up the motor to full power and
then unplug the battery with the motor
running. The next time you plug it in it will fry
because it was fried when you pulled off the
battery the previous time.”
That seems similar to what Doug noted
about running at full throttle and pulling the
battery connection. Judging from Doug’s and
Keith’s comments it seems highly unlikely
that an in-line meter was the cause of the
“failure,” but it could have contributed
slightly if the system was already on the
“verge.”
The bottom line is not to disconnect or
switch off your battery when running wideopen
throttle.
98 MODEL AVIATION
Models with new plastic cowlings installed.
Cowling parts the author made from plastic bottles.
01sig4.QXD 11/20/07 8:56 AM Page 98
batteries built in that quit. I have a similar one
and was sorry to find that it is no longer
manufactured, nor are replacement packs
readily available. We have found them ideal
for hobby use.
Since these packs were made from short
Sub-C cells (4/5 Sub-C), I suggested he get in
touch with NoBS Batteries (via Hangtimes
Hobbies); perhaps he could get help there. The
company built him the custom pack and I
installed it, bringing the drill back to life. I
have since needed a three-cell stick for my
cordless screwdriver, and NoBS Batteries
came through on that.
Steve Anthony, NoBS Batteries owner,
can custom-build almost any pack (from
quality Sanyo cells) you might need. All you
have to do is give him the configuration of the
pack you want.
The Web site has an excellent frequentlyasked
questions section that will answer many
of your battery questions. Steve was with SR
Batteries for sometime and understands what
it takes to assemble a quality pack, be it for
your RC use or something special.
VoltMagic has added selectable Peak Low
Voltage (PLV) ranges to its 2RY series of inflight
voltage monitors. You can upgrade any
VoltMagic to version 2RZ with Normal and
Low Range PLV, Extended PLV, 16 voltage
ranges, 1,000 samples/second, etc.
100 MODEL AVIATION
The 2R models have two red LEDs and
2Y models have two yellow LEDs. Otherwise
they have the same version-Z features and
specifications.
Upgrades are $9.95 each plus $1.95
shipping and handling. For return shipping
instructions, send an E-mail to Upgrade@
VoltMagic.com. The upgrade is free (only
$1.95 for shipping and handling) if you
purchased your unit after August 1, 2007.
(You must include the dated receipt.)
Now that you have converted your .40
engine-powered airplane to electric, how do
you cover the ugly hole where the engine
was? Looking around the kitchen pantry I
found the answer: make cowlings from plastic
bottles.
Mounting them is simplified by making a
3/32 plywood circle with enough of the center
cut out to fit over the motor and mounts, to fit
snugly inside the bottle that you have trimmed
to the length needed. Glue 1/4 square x 1/2
hardwood where you want to attach the
cowling, round them off flush with the
plywood, and then locate the whole thing on
the existing firewall. Paint with automotive
primer and then the color of your choice.
I hope 2008 is a great year for you and you
get all the flying you deserve. Keep those
cards and letters coming so I know what you
want to see in this column. MA
Sources:
Hangtimes Hobbies
(631) 610-5169
www.hangtimes.com/index.html
SLK Electronics
(336) 676-1681
www.slkelectronics.com
VoltMagic
Box 1518
Estacada OR 97023
www.voltmagic.com
The Battery Clinic
12219 NW 9th Ln.
Newberry FL 32669
www.rcbatteryclinic.com
01sig4.QXD 11/20/07 8:56 AM Page 100

92 MODEL AVIATION
DO YOU
remember the
electrical charging
station I described
in a recent column?
Dave Sweeney
designed it, and
Willie Gardner built
it with a solar panel
hooked to a storage
battery and shelves
attached to a metal
building so that
flight packs are in a
safe and visible area
during recharge.
I neglected to
mention the topnotch
work Willie
and Dave did on
this project; in fact,
I didn’t print their
names at all.
Unfortunately space
is limited, or I
would have let them see their names in MA this month.
Dave Sweeney and Willie Gardner deserve proper credit,
especially since their invention is so popular that they are planning
to expand the electrical storage system to provide more charging
power on cloudy days.
E-mail has rolled in lately to tell me what a goof I made when I
mentioned prescription eyeglasses but didn’t say that such glasses
alone don’t provide full protection when using power tools. More than
Safety Comes First Dave Gee | [email protected]
Solar-powered battery storage and charging station
Also included in this column:
• Proper eye protection for
power-tool use
• Why impound a Spektrum
radio?
• Shattering info about broken
cutoff wheels
• Using low-rated switches in
high-power circuits
• This month’s photos
• Review of the fun CL system
by P3 Models
Nikki Robichau is learning to fly her RC helicopter with her dad’s
help. Kids have quick reflexes and can develop RC flying skills
faster than adults can.
Mark Miller makes sure other fliers can locate and identify his
models by putting photos on his frequency pins.
P3 Models’ Revolution allows a CL pilot to fly from outside the
circle. This column contains a review of the system.
01sig3.QXD 11/19/07 3:08 PM Page 92
one eye doctor reminded me that particles
can easily ricochet around standard glasses
and that we need to use protection that
fully covers the eyes. I should have made
that clear!
There used to be little plastic end pieces
that would clip onto glasses and provide
side coverage. You could see them used at
any machine shop, but lately I’ve been
unable to find such a product. My glasses
are oversized and leave no gaps at my nose
or cheek, but the sides are still wide open.
If you know of a source for the clip-on
side pieces I described, please E-mail me
or send a note to Box 7081, Van Nuys CA
91409. You can also use these addresses to
let me know how I goofed up this month.
Walt Keating thought he had me on a
transmitter impound story, and he E-mailed
his thoughts.
“In your story about a recent fun-fly,
you stated that even the new Spektrum
system users understood that their radios
belonged on the impound table. May I ask
why?
“I recently attended Top Gun here in
Florida and I can assure you that no
Spektrum user was subjected to impound
nor was there any ‘understanding’ relative
to that issue. Spektrum radios do not
require impound because they are not
subject to interference like older systems.”
Walt, I realize that interference is a
nonissue with the new radios. But we are
in a transition period, and that meet was
many months ago when some fliers had
still never even seen a Spektrum system.
They impounded the radios for
consistency, to make sure some new guy
didn’t see a nonimpounded transmitter in
use in the pits and figure he could do the
same with his 72 MHz system.
It probably won’t be long before this
precaution is no longer needed, but at the
time it was a good idea. You have to figure
things by imagining what the dumbest guy
on the field will do. (When I am not
present they pick a new dumbest guy.)
Another omission of mine was corrected
by Jeff Hails, who wrote:
94 MODEL AVIATION
“I was glad to see some discussion of
safety with cutoff wheels. I grew up building
slot car chassis and cutoff wheels were the tool
of choice for cutting spring steel and brass
sheet, or piano wire. The first lesson I learned
was never, ever put your body in the plane of
the wheel.”
Jeff is absolutely right, and I should have
covered that point. Visualizing an imaginary
extension of the cutting disk is hard for some,
but that is where things will fly if the wheel
shatters.
The same is true of propellers. The “plane”
of the spinning blades is a danger zone, and it
is a good idea to minimize our exposure to this
area.
It helps me to picture the vertical lines that
were sometimes painted on the fuselage of
bombers to warn ground crews about the
presence of a spinning propeller. The lines
mark an extension of the propeller disk as it
meets the airplane.
This reminder keeps my mind on “what
might happen if ... ” and I try to position my
work such that the edge of the cutting disk
does not line up with my body parts.
I received an informative message from
Camille Goudeseune, who is a columnist for
Quiet Flyer magazine. He wrote:
“You mentioned that arming switches can
be difficult for high-current electric motors.
This is not necessarily true. You can use a
switch rated for low current at much higher
currents—as long as you don’t move the
switch when high current would flow across it,
arcing the contacts.
“So you don’t need a heavy 50-amp
industrial knife-blade switch on board. Just
zero the throttle before you arm or disarm.”
He is right, but I am the wrong guy to have
such a setup since my policy is to commit
whatever goofs are possible. If you are more
organized and disciplined than I am, Camille’s
information could save you some onboard
weight and provide a little performance boost.
Camille also complimented this column’s
“density.” I’m pretty sure he meant that I cram
a lot of stuff in each month and was not
making a comment about my mental prowess
(or lack thereof). Such flattery!
01sig3.QXD 11/19/07 3:09 PM Page 94
Look at the picture showing frequency
pins with photos on them. Mark Miller
made these, and he assured me that it is not
a new idea. It was new to me, and I think
Mark is clever for making it easy for other
pilots to identify which model is on a given
channel. (The little photos don’t do justice
to his beautiful models!)
The other photo shows Nikki Robichau
with her electric helicopter. Note the
training skids that she uses while her dad
teaches her to fly. Nikki flies a Blade CX2,
which uses a Spektrum-equipped E-flite
radio.
She thought it was funny that I
photographed her instead of the other
helicopter pilots at the field. Model
aviation is a relaxing hobby that brings
generations together, and it makes them
shout “pull up!” at each other.
Many AMA members came into modeling
via RC and have never flown a CL model.
What a shame! The distinctive “vroom,
vroom” sound as a model races around the
circle reminds me of the days when gas CL
was the big thing.
At the last AMA Convention I visited
the P3 Models booth and saw its
Revolution system: a setup that allows you
to fly CL from outside the circle. I was
interested in this product, and when the
chance came to review it I eagerly
volunteered. It is a great item and a fun
way to fly a model.
The Revolution is basically a sturdy
swiveling linkage that allows a pilot to fly
a CL aircraft while standing still, outside
the circle. A number of products through
the years have tried to accomplish this, but
the Revolution impressed me with its solid
engineering and thoughtful design. It really
works as advertised.
The center post has a swiveling head
that takes the pull of the model and
transmits control input from the pilot’s
handle. The parts are ruggedly built, but
you wouldn’t want to leave the Revolution
out in the weather.
Setup is easy enough for even a
columnist to do. P3 Models has a great
video on its Web site that takes you
through the process.
The components break down to fit into a
handy storage box, but the system doesn’t
have to be fully disassembled every time
you take it down. Leaving some of the
parts hooked up saves time and doesn’t
take up much space. A DVD comes in the
package and is available separately.
One person can start and fly the model
without help or a stooge (not that I
recommend operating a gas model alone at
the field!), and the Revolution is especially
good for disabled modelers who might not
be able to turn ’round and ’round with a
conventional CL aircraft.
Those who get too dizzy to fly CL
would also be excellent candidates for the
Revolution. (I’ve never gotten dizzy flying
CL, even on very short lines, because I was
taught to concentrate on the model rather
than on the passing scenery.) Student pilots
can stand still with an instructor and not
worry about the airplane’s weight as they
fly.
The swiveling control head allows for
level flight, climbs and dives, and semi-
Wingovers. You can’t do the CL
Aerobatics (Stunt) pattern with the
Revolution, but I couldn’t do the Stunt
pattern even if I were channeling the spirit
of Jim Walker.
There is no whipping possible, and the
“feel” of being connected to the model (a
special benefit of CL flying) is much more
subtle than with conventional CL but still
noticeable.
The standard version of the Revolution
that I tested is designed for a full-size gas
or electric CL model. It needs a grass field
because the center pylon is staked down. I
understand that the company is working on
a smaller version for 1/2A models and
possibly a way to use the system on a
paved circle.
The Revolution’s introductory price is
$299.99, which strikes me as quite a
bargain for such a high-quality unit. MA
Sources:
P3 Models
(800) 515-5951
www.p3models.com
96 MODEL AVIATION
01sig3.QXD 11/19/07 3:09 PM Page 96
Banana plugs that fit into alligator clips is a great idea
January 2008 97
The Battery Clinic Red Scholefield | [email protected]
Also included in this column:
• Don’t smoke your ESC
• New cell tester for Li-Polys
and A123 packs
• VoltMagic upgrade
• Cover that ugly hole where
your glow engine was
The SLK Electronics B1 cell tester.
Modify your own alligator clips to accept banana plugs.
New Cellpro charger with convertible alligator clips.
I’M GLAD TO see that charger
manufacturers have finally figured it out.
Following the lead of Triton 2 and TME’s
Xtrema, FMA Direct is now shipping its
popular Cellpro charger balancer with banana
leads and alligator clips that plug into each
other.
Most serious electric-power fliers have set
up their chargers with banana plugs so they
can easily connect to bench power supplies or
cigarette-lighter plugs modified to accept
banana jacks. The photograph with the
alligator clip shows this simple modification
using a 7/8-inch length of 3/16-inch-diameter
brass tubing and soldering to the inside of the
alligator clip.
The following is not necessarily about
batteries, but it is an interesting discussion
about wattmeters. A reader wrote:
“I smoked my 80 amp ESC this weekend
while running the EDF on the bench. The
vendor says it’s due to my having a
Whattmeter in series when I ran the motor.
The Whattmeter introduces resistance thereby
increasing the ripple beyond what the input
capacitors can handle so it blew up the Power
MOSFETS and most of the power board.
“They recommend that we do not use any
kind of wattmeter to measure power if the
current draw is expected to exceed 25 amps or
so, but instead use a DC clamp on meter like
what you can get at Sears. Not that accurate
but close enough and prevents blowing up
ESC.”
I thought to myself, How could this be? If
it were true, people would be blowing ESCs
all over the place. I’ve used my wattmeter on
a number of different ESCs with no problem.
Nevertheless, consulting the experts wasn’t a
bad idea. Following is a compilation of a
number of conversations with Keith Shaw,
Doug Ingraham (designer of the Whattmeter),
Greg Gimlick, Greg Covey, and Ken Myers.
01sig4.QXD 11/20/07 8:56 AM Page 97
Balancing Ni-Cd/NiMH Vs. Lithium Batteries: There seems to be a bit
of confusion about this. No one ever thought much about balancing
Nickel technology packs. It happened automatically if you used them
with any charger that had a trickle capability after peak charging or you
were using the wall-wart charger that came with your radio system.
Since those are constant-current devices when it comes to charging,
all the cells, if left on trickle, came to their maximum state of charge
because they were getting the same current and could stand some
amount of overcharge.
Lithium systems are different. They are constant-voltage systems,
which means you charge the cells to a specific level and then stop. Each
cell must be brought up to that level to balance the pack. This is where
the problem occurs.
When you are charging them in series as they are always used, the
charger looks for X multiplied by 4.2 volts. So in a 3S pack it is looking
for 12.6 volts. Forget that this pack is labeled 11.1; that is the nominal
voltage.
Suppose that one cell is charged before its neighbors for some
reason. It can be driven to a higher voltage, while the others have yet to
reach 4.2 (the cell’s peak voltage). Going beyond 4.2 volts is
detrimental to cell life. Hence we have to balance each cell individually,
which is what a properly designed balancing charger does.
This should not come as a great shock since large banks of lead-acid
batteries used in emergency power situations go through frequent cellbalancing
procedures for the same reason that Lithium cells require it.
Lead-acid is a constant-voltage system.
SLK Electronics B1: Sid Kauffman has come up with another handy
battery tool: a cell tester/balancer. It was conceived as an economical
cell balancer for M1 (A123Systems) batteries.
My field experience has shown that these cells stay in balance well.
It is normally necessary to check them only periodically. The problem
is that the cell-voltage differences are tiny during charge until almost
full.
If M1 cells are checked at the end of charge, they frequently appear
to be unbalanced when they are not. Conversely, if checked when not
fully charged, they can appear to be balanced when they are not.
The B1 cell tester allows you to measure each cell voltage (one at a
time) using the balancing tap connector and either charge or discharge
each cell. It can also be used to check and balance your Li-Poly cells
one at a time. This device measures cell voltage from 2.8 to 5.8 with a
5.0-millivolt resolution. You can also use it to check your four-cell
receiver packs.
Three pages of detailed operating instructions for the B1 are
provided on the SLK Web site. To learn more about the unit you can
also read the instructions, which are posted on the site in PDF format.
What would you do if your favorite cordless tool died? Don’t despair.
One of my fellow club members had a small Makita drill with the
Doug said:
“Adding the Whattmeter should not be the cause of a problem.
The wattmeter is a minor resistance source. About the same as adding
a length of 13 gauge wire of whatever length the leads are.
“The positive lead is nothing more than a wire with a tap. The
negative lead has a precision non inductive shunt in the line which is
only slightly higher than the equivalent length of wire. The battery
resistance is orders of magnitude greater than the wattmeter.
“In my opinion this was not the cause of the ESC burning up.
There must have been some other contributing factor.
“The addition of much longer leads in the circuit (several
additional feet) would be needed for the inductance to be a problem.
The inductance in the wires between the battery and the ESC while
small can cause the voltage to spike when the MOSFET switches are
turned off in the ESC. The absorption of these spikes are the purpose
of the input capacitor. An increase in current makes this more likely.
Damage to the MOSFETs is cumulative.”
As near as I can recall, the following was second-hand via Greg
Gimlick, I think, from Keith Shaw.
“The other source of high voltage spikes that can’t be controlled so
much by the input capacitor is on the motor
side. These spikes are shunted back into the
battery by the body diodes of the MOSFET.
“The inductance of the motor is huge
(which is especially true of outrunners). I can
almost guarantee that a way to kill a speed
control is to run up the motor to full power and
then unplug the battery with the motor
running. The next time you plug it in it will fry
because it was fried when you pulled off the
battery the previous time.”
That seems similar to what Doug noted
about running at full throttle and pulling the
battery connection. Judging from Doug’s and
Keith’s comments it seems highly unlikely
that an in-line meter was the cause of the
“failure,” but it could have contributed
slightly if the system was already on the
“verge.”
The bottom line is not to disconnect or
switch off your battery when running wideopen
throttle.
98 MODEL AVIATION
Models with new plastic cowlings installed.
Cowling parts the author made from plastic bottles.
01sig4.QXD 11/20/07 8:56 AM Page 98
batteries built in that quit. I have a similar one
and was sorry to find that it is no longer
manufactured, nor are replacement packs
readily available. We have found them ideal
for hobby use.
Since these packs were made from short
Sub-C cells (4/5 Sub-C), I suggested he get in
touch with NoBS Batteries (via Hangtimes
Hobbies); perhaps he could get help there. The
company built him the custom pack and I
installed it, bringing the drill back to life. I
have since needed a three-cell stick for my
cordless screwdriver, and NoBS Batteries
came through on that.
Steve Anthony, NoBS Batteries owner,
can custom-build almost any pack (from
quality Sanyo cells) you might need. All you
have to do is give him the configuration of the
pack you want.
The Web site has an excellent frequentlyasked
questions section that will answer many
of your battery questions. Steve was with SR
Batteries for sometime and understands what
it takes to assemble a quality pack, be it for
your RC use or something special.
VoltMagic has added selectable Peak Low
Voltage (PLV) ranges to its 2RY series of inflight
voltage monitors. You can upgrade any
VoltMagic to version 2RZ with Normal and
Low Range PLV, Extended PLV, 16 voltage
ranges, 1,000 samples/second, etc.
100 MODEL AVIATION
The 2R models have two red LEDs and
2Y models have two yellow LEDs. Otherwise
they have the same version-Z features and
specifications.
Upgrades are $9.95 each plus $1.95
shipping and handling. For return shipping
instructions, send an E-mail to Upgrade@
VoltMagic.com. The upgrade is free (only
$1.95 for shipping and handling) if you
purchased your unit after August 1, 2007.
(You must include the dated receipt.)
Now that you have converted your .40
engine-powered airplane to electric, how do
you cover the ugly hole where the engine
was? Looking around the kitchen pantry I
found the answer: make cowlings from plastic
bottles.
Mounting them is simplified by making a
3/32 plywood circle with enough of the center
cut out to fit over the motor and mounts, to fit
snugly inside the bottle that you have trimmed
to the length needed. Glue 1/4 square x 1/2
hardwood where you want to attach the
cowling, round them off flush with the
plywood, and then locate the whole thing on
the existing firewall. Paint with automotive
primer and then the color of your choice.
I hope 2008 is a great year for you and you
get all the flying you deserve. Keep those
cards and letters coming so I know what you
want to see in this column. MA
Sources:
Hangtimes Hobbies
(631) 610-5169
www.hangtimes.com/index.html
SLK Electronics
(336) 676-1681
www.slkelectronics.com
VoltMagic
Box 1518
Estacada OR 97023
www.voltmagic.com
The Battery Clinic
12219 NW 9th Ln.
Newberry FL 32669
www.rcbatteryclinic.com
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