Left
ESC
Right
ESC
Differential motor steering
February 2008 89
? Frequently Asked Questions Bob Aberle | [email protected]
Also included in this column:
• Covering-material weight
• Silver solder
Above: Bob’s fantasy scale Burnelli CBY-3. The prototype model did
not employ movable twin rudders, so it was impossible to steer on
the ground. Differential motor steering solved the problem.
Left: Bob’s CBY-3 used two AXi 2204/54 brushless outrunners.
Having separate ESCs allows you to use differential motor steering.
Below: This shows how two brushless motors and separate
brushless ESCs can provide differential motor steering.
Differential
Motor Steering
Left
Motor
Right
Motor
Receiver
Transmitter
CH3 CH6
Left
Rudder
Right
Motor
Speeds Up
Airplane
Goes Left
PLEASE WRITE IN with your questions, since that is the only
way we can keep this column format going. When referring to
already published Q/As (for follow-ups), always provide the
number as a reference.
Q333: “I recently purchased a micro RC aircraft that is powered
by a pair of electric motors. Instead of steering this plane with a
rudder or ailerons, it is controlled by varying the speeds of each
motor. I believe this is referred to as ‘differential motor steering.’
I was wondering if this same concept might be applied to larger
size electric powered aircraft.”
A333: In the November 2007 column I wrote about multiplebrushless-
motor operation and the fact that each motor requires a
separate brushless ESC. The problem, as I pointed out, is that with
separate ESCs the cost and weight goes up with each added motor.
When we used brushed motors, a single ESC could control all of
them.
But despite the increased cost and weight, there is an
interesting advantage to having separate ESCs: you have the
ability to set up your electric power system for differential motor
steering. By speeding up one motor vs. the other (in a twin
02sig3.QXD 12/20/07 12:21 PM Page 8990 MODEL AVIATION
Iron-on covering materials’ weight can be
critical to certain models. A feature about
this subject is planned for MA, but in the
meantime Bob offers suggestions.
On a Polk’s Tracker III the CH 6 knob must be positioned for mid servo range. A
reference mark is made at that position. (The X-Acto knife points to it.) All three mixes
are assigned to switch C, which must be turned on (up).
A dual-landing-wheel Scale-model application required separate axles. The two wires
were wrapped with soft copper wire and silver-soldered together.
Assembling wire pieces for special landinggear
applications is best done with silver
solder and flux known as Stay-Brite.
configuration), the model can be steered on
the ground and, to a degree, in the air as if
it had articulated rudder(s).
The model I showed in the November
column was my new Burnelli CBY-3
“Loadmaster” lifting-body transport. By
the time you read this it should have been
featured in a construction article in Air
Age’s January 2008 Backyard Flyer
magazine. To keep the design simple I did
not resort to rudder control (only ailerons
and elevator).
Hooking up twin operating rudders can
pose problems. Unfortunately this
particular lifting-body design proved to be
hard to grip when hand launching the
model. Without rudders there was no way
to steer a straight course on the ground for
a takeoff.
I did some checking and took an idea
from my flying partner, Tom (Mr. NEAT
Fair) Hunt. This scheme is generally not
mentioned in RC-system handbooks or
operating manuals. To do this job right
you will need a programmable RC
transmitter along with a six-channelcapable
receiver. A five-channel receiver
will not fit this application and, in fact,
could be dangerous depending on where
your retract switch was set.
(Editor’s note: Channel 5 isn’t
proportional on all radio systems and/or
its switch can’t be deactivated.)
To make this control scheme work you
need a separate ESC operating each of the
two brushless motors (which should
always be the case). On the aircraft side,
the ESC for the left-side motor (looking
from the rear of the model forward) goes
to receiver port No. 3. The ESC for the
right-side motor goes to receiver port No.
6.
I used a Polk’s Tracker III transmitter.
First, I went to PMIX 1 and set CH 3 as
Master, CH 6 as Slave, and the mix at
+100%. Second, I went to PMIX 2 and set
CH 4 as Master, CH 3 as Slave, and the
02sig3.QXD 12/20/07 12:29 PM Page 90mix at +30%. Third, I went to PMIX 3 and
set CH 4 as Master and CH 6 as Slave
with the mix at –30%.
It is most important that you limit
yourself to 30% on PMIX 2 and 3, and
make sure that one is positive while the
other is negative. If the motors work
opposite to each other, reverse the + and –
or swap channels 3 and 6 at the receiver.
Now for the tricky part. The Tracker III
transmitter’s CH 6 control function is
managed by a rotary knob. That channel
must be preset to the neutral position. To
do this, plug a servo with a long output
arm into your receiver’s aileron or elevator
channel function and set the transmitter
trim lever for that channel to neutral. (And
make sure no memory trim was being used
on that channel.) Make sure the servo
output arm is at 90° to the servo case.
Plug that servo into your receiver’s CH
6 port and rotate the knob for the same
midrange position, where the servo arm is
again at 90° to the case. After doing this I
made a mark with a pen next to the knob
92 MODEL AVIATION
Celebrating30Years!
- SECURE SHOPPING WITH OUR ONLINE CATALOG -
www.fiberglassspecialtiesinc.com
[email protected]
Phone (479) 359-2429 Fax (479) 359-2259
Hours: Monday - Friday 9 to 5 CST
15715 Ashmore Dr., Garfield, Arkansas 72732
LARGEST COLLECTION OF
EPOXY GLASS COWLS &
WHEEL PANTS IN THE WORLD!
Download a Free Catalog from the World's
Largest Manufacturer of Model Airplane
Cowls, Wheelpants & Accessories.
to make sure it wasn’t accidentally rotated
to another position. You might also
consider placing tape over that control
knob.
The other thing you must do is go to
the Switch Assign portion of the
transmitter menu and assign PMIX 1,
PMIX 2, and PMIX 3 to Switch C. With
that switch in the upper position (No. 1),
all three mixes will be activated. Don’t
touch that switch again!
Having done all this, your transmitter
throttle control stick will run both motors
together at speeds from idle to full. This is
what you will normally use in flight.
Rocking the transmitter rudder control
stick from side to side will vary the
motors’ speeds. If you apply right rudder,
the motor on the left side will run faster
than the one on the right. If you apply left
rudder, control will do the reverse. That’s
the differential. It allows for steering on
the ground as if you had articulated
(moving) rudders on your aircraft, but with
much less work.
These instructions apply to a Polk’s
Tracker III transmitter, but other brands of
systems should work in roughly the same
manner. You might want to contact other
manufacturers for the details.
The success I had with this differential
steering is going to prompt me to design
many more electric-powered twins.
Q334: “I have an application for iron-on
covering where the weight of the material
may be critical. Is there any information
available that compares the weights of the
various iron-on covering material now on
the market?”
A334: I thought this subject had been
covered in the past. However, after an
extensive search I realized that much has
changed through the years and some older
products are gone and newer ones have
taken their place.
The entire topic of iron-on covering
material, the weight, intended application,
and application technique needs a
considerable update. This was discussed
with AMA’s Publications Department, and
a feature article is planned on this subject.
In the meantime I came up with an
interesting weight-comparison table that is
presented on the Internet.
In addition there are two excellent
books by Faye Stilley: Covering R/C
Airplanes, volumes 1 and 2, published by
Air Age Media (which publishes Model
Airplane News). Faye is an iron-oncovering
application master. The books are
available from the AMA Supply and
Service or go to the AMA Web site and
select “Shop AMA,” “Browse our
Catalog,” “Books and DVDs,” and then
scroll to these two volumes.
02sig3.QXD 12/20/07 12:21 PM Page 92Q335: “I’m having trouble soldering such
things as landing gear wire and braces
using conventional solder. I understand
there may be a better type solder available
to do this kind of job. Can you help me?”
A335: Many modelers try to use the more
common rosin core (electrical) solder for
this kind of application. For joining wire,
as is the case with landing gear, you should
be using silver solder. This type of solder
has been on the market for years, usually
under the trade name Stay-Brite. It is
manufactured by The Harris Products
Group.
I’m sure this product has many
distributors across the country. One is
Riverside Machine Shop Inc. of DeQueen,
Arkansas. The silver solder and special
liquid flux are supplied as a kit. One will
last for quite a while and costs $12 plus
shipping.
When using this solder, make sure you
have enough heat. I use a 50-watt iron with
a good-size chisel tip. For most applications
you will be joining several lengths of wire.
Before soldering I wrap the wire with bare
copper wire. You can easily pull some
strands of that from common zip cord.
(Editor’s note: Don’t forget to
thoroughly clean all the metal with Emery
paper.)
Apply the liquid flux and then bring
your hot iron and silver solder to the
intended joint. The shiny flow of solder is
a sign that you’ll have a strong joint. A
photo shows a recent landing-gear strut I
assembled with silver solder.
Don’t use this solder or flux on any
electrical wiring; it is highly corrosive. In
fact, when you are finished making a wire
joint it’s a good idea to clean the soldered
area with denatured alcohol and an old
toothbrush. This will remove any flux
residue. MA
Sources:
AMA
(765) 287-1256
www.modelaircraft.org
Weights of Covering Materials
http://webpages.charter.net/rcfu/HelpsHint
s/IOCWeight.html
Riverside Machine Shop Inc.
(870) 642-7643
www.riversidemachine.net/item17134.ctlg
The Harris Products Group
(800) 733-4043
www.harrisproductsgroup.com
Edition: Model Aviation - 2008/02
Page Numbers: 89,90,92,94
Edition: Model Aviation - 2008/02
Page Numbers: 89,90,92,94
Left
ESC
Right
ESC
Differential motor steering
February 2008 89
? Frequently Asked Questions Bob Aberle | [email protected]
Also included in this column:
• Covering-material weight
• Silver solder
Above: Bob’s fantasy scale Burnelli CBY-3. The prototype model did
not employ movable twin rudders, so it was impossible to steer on
the ground. Differential motor steering solved the problem.
Left: Bob’s CBY-3 used two AXi 2204/54 brushless outrunners.
Having separate ESCs allows you to use differential motor steering.
Below: This shows how two brushless motors and separate
brushless ESCs can provide differential motor steering.
Differential
Motor Steering
Left
Motor
Right
Motor
Receiver
Transmitter
CH3 CH6
Left
Rudder
Right
Motor
Speeds Up
Airplane
Goes Left
PLEASE WRITE IN with your questions, since that is the only
way we can keep this column format going. When referring to
already published Q/As (for follow-ups), always provide the
number as a reference.
Q333: “I recently purchased a micro RC aircraft that is powered
by a pair of electric motors. Instead of steering this plane with a
rudder or ailerons, it is controlled by varying the speeds of each
motor. I believe this is referred to as ‘differential motor steering.’
I was wondering if this same concept might be applied to larger
size electric powered aircraft.”
A333: In the November 2007 column I wrote about multiplebrushless-
motor operation and the fact that each motor requires a
separate brushless ESC. The problem, as I pointed out, is that with
separate ESCs the cost and weight goes up with each added motor.
When we used brushed motors, a single ESC could control all of
them.
But despite the increased cost and weight, there is an
interesting advantage to having separate ESCs: you have the
ability to set up your electric power system for differential motor
steering. By speeding up one motor vs. the other (in a twin
02sig3.QXD 12/20/07 12:21 PM Page 8990 MODEL AVIATION
Iron-on covering materials’ weight can be
critical to certain models. A feature about
this subject is planned for MA, but in the
meantime Bob offers suggestions.
On a Polk’s Tracker III the CH 6 knob must be positioned for mid servo range. A
reference mark is made at that position. (The X-Acto knife points to it.) All three mixes
are assigned to switch C, which must be turned on (up).
A dual-landing-wheel Scale-model application required separate axles. The two wires
were wrapped with soft copper wire and silver-soldered together.
Assembling wire pieces for special landinggear
applications is best done with silver
solder and flux known as Stay-Brite.
configuration), the model can be steered on
the ground and, to a degree, in the air as if
it had articulated rudder(s).
The model I showed in the November
column was my new Burnelli CBY-3
“Loadmaster” lifting-body transport. By
the time you read this it should have been
featured in a construction article in Air
Age’s January 2008 Backyard Flyer
magazine. To keep the design simple I did
not resort to rudder control (only ailerons
and elevator).
Hooking up twin operating rudders can
pose problems. Unfortunately this
particular lifting-body design proved to be
hard to grip when hand launching the
model. Without rudders there was no way
to steer a straight course on the ground for
a takeoff.
I did some checking and took an idea
from my flying partner, Tom (Mr. NEAT
Fair) Hunt. This scheme is generally not
mentioned in RC-system handbooks or
operating manuals. To do this job right
you will need a programmable RC
transmitter along with a six-channelcapable
receiver. A five-channel receiver
will not fit this application and, in fact,
could be dangerous depending on where
your retract switch was set.
(Editor’s note: Channel 5 isn’t
proportional on all radio systems and/or
its switch can’t be deactivated.)
To make this control scheme work you
need a separate ESC operating each of the
two brushless motors (which should
always be the case). On the aircraft side,
the ESC for the left-side motor (looking
from the rear of the model forward) goes
to receiver port No. 3. The ESC for the
right-side motor goes to receiver port No.
6.
I used a Polk’s Tracker III transmitter.
First, I went to PMIX 1 and set CH 3 as
Master, CH 6 as Slave, and the mix at
+100%. Second, I went to PMIX 2 and set
CH 4 as Master, CH 3 as Slave, and the
02sig3.QXD 12/20/07 12:29 PM Page 90mix at +30%. Third, I went to PMIX 3 and
set CH 4 as Master and CH 6 as Slave
with the mix at –30%.
It is most important that you limit
yourself to 30% on PMIX 2 and 3, and
make sure that one is positive while the
other is negative. If the motors work
opposite to each other, reverse the + and –
or swap channels 3 and 6 at the receiver.
Now for the tricky part. The Tracker III
transmitter’s CH 6 control function is
managed by a rotary knob. That channel
must be preset to the neutral position. To
do this, plug a servo with a long output
arm into your receiver’s aileron or elevator
channel function and set the transmitter
trim lever for that channel to neutral. (And
make sure no memory trim was being used
on that channel.) Make sure the servo
output arm is at 90° to the servo case.
Plug that servo into your receiver’s CH
6 port and rotate the knob for the same
midrange position, where the servo arm is
again at 90° to the case. After doing this I
made a mark with a pen next to the knob
92 MODEL AVIATION
Celebrating30Years!
- SECURE SHOPPING WITH OUR ONLINE CATALOG -
www.fiberglassspecialtiesinc.com
[email protected]
Phone (479) 359-2429 Fax (479) 359-2259
Hours: Monday - Friday 9 to 5 CST
15715 Ashmore Dr., Garfield, Arkansas 72732
LARGEST COLLECTION OF
EPOXY GLASS COWLS &
WHEEL PANTS IN THE WORLD!
Download a Free Catalog from the World's
Largest Manufacturer of Model Airplane
Cowls, Wheelpants & Accessories.
to make sure it wasn’t accidentally rotated
to another position. You might also
consider placing tape over that control
knob.
The other thing you must do is go to
the Switch Assign portion of the
transmitter menu and assign PMIX 1,
PMIX 2, and PMIX 3 to Switch C. With
that switch in the upper position (No. 1),
all three mixes will be activated. Don’t
touch that switch again!
Having done all this, your transmitter
throttle control stick will run both motors
together at speeds from idle to full. This is
what you will normally use in flight.
Rocking the transmitter rudder control
stick from side to side will vary the
motors’ speeds. If you apply right rudder,
the motor on the left side will run faster
than the one on the right. If you apply left
rudder, control will do the reverse. That’s
the differential. It allows for steering on
the ground as if you had articulated
(moving) rudders on your aircraft, but with
much less work.
These instructions apply to a Polk’s
Tracker III transmitter, but other brands of
systems should work in roughly the same
manner. You might want to contact other
manufacturers for the details.
The success I had with this differential
steering is going to prompt me to design
many more electric-powered twins.
Q334: “I have an application for iron-on
covering where the weight of the material
may be critical. Is there any information
available that compares the weights of the
various iron-on covering material now on
the market?”
A334: I thought this subject had been
covered in the past. However, after an
extensive search I realized that much has
changed through the years and some older
products are gone and newer ones have
taken their place.
The entire topic of iron-on covering
material, the weight, intended application,
and application technique needs a
considerable update. This was discussed
with AMA’s Publications Department, and
a feature article is planned on this subject.
In the meantime I came up with an
interesting weight-comparison table that is
presented on the Internet.
In addition there are two excellent
books by Faye Stilley: Covering R/C
Airplanes, volumes 1 and 2, published by
Air Age Media (which publishes Model
Airplane News). Faye is an iron-oncovering
application master. The books are
available from the AMA Supply and
Service or go to the AMA Web site and
select “Shop AMA,” “Browse our
Catalog,” “Books and DVDs,” and then
scroll to these two volumes.
02sig3.QXD 12/20/07 12:21 PM Page 92Q335: “I’m having trouble soldering such
things as landing gear wire and braces
using conventional solder. I understand
there may be a better type solder available
to do this kind of job. Can you help me?”
A335: Many modelers try to use the more
common rosin core (electrical) solder for
this kind of application. For joining wire,
as is the case with landing gear, you should
be using silver solder. This type of solder
has been on the market for years, usually
under the trade name Stay-Brite. It is
manufactured by The Harris Products
Group.
I’m sure this product has many
distributors across the country. One is
Riverside Machine Shop Inc. of DeQueen,
Arkansas. The silver solder and special
liquid flux are supplied as a kit. One will
last for quite a while and costs $12 plus
shipping.
When using this solder, make sure you
have enough heat. I use a 50-watt iron with
a good-size chisel tip. For most applications
you will be joining several lengths of wire.
Before soldering I wrap the wire with bare
copper wire. You can easily pull some
strands of that from common zip cord.
(Editor’s note: Don’t forget to
thoroughly clean all the metal with Emery
paper.)
Apply the liquid flux and then bring
your hot iron and silver solder to the
intended joint. The shiny flow of solder is
a sign that you’ll have a strong joint. A
photo shows a recent landing-gear strut I
assembled with silver solder.
Don’t use this solder or flux on any
electrical wiring; it is highly corrosive. In
fact, when you are finished making a wire
joint it’s a good idea to clean the soldered
area with denatured alcohol and an old
toothbrush. This will remove any flux
residue. MA
Sources:
AMA
(765) 287-1256
www.modelaircraft.org
Weights of Covering Materials
http://webpages.charter.net/rcfu/HelpsHint
s/IOCWeight.html
Riverside Machine Shop Inc.
(870) 642-7643
www.riversidemachine.net/item17134.ctlg
The Harris Products Group
(800) 733-4043
www.harrisproductsgroup.com
Edition: Model Aviation - 2008/02
Page Numbers: 89,90,92,94
Left
ESC
Right
ESC
Differential motor steering
February 2008 89
? Frequently Asked Questions Bob Aberle | [email protected]
Also included in this column:
• Covering-material weight
• Silver solder
Above: Bob’s fantasy scale Burnelli CBY-3. The prototype model did
not employ movable twin rudders, so it was impossible to steer on
the ground. Differential motor steering solved the problem.
Left: Bob’s CBY-3 used two AXi 2204/54 brushless outrunners.
Having separate ESCs allows you to use differential motor steering.
Below: This shows how two brushless motors and separate
brushless ESCs can provide differential motor steering.
Differential
Motor Steering
Left
Motor
Right
Motor
Receiver
Transmitter
CH3 CH6
Left
Rudder
Right
Motor
Speeds Up
Airplane
Goes Left
PLEASE WRITE IN with your questions, since that is the only
way we can keep this column format going. When referring to
already published Q/As (for follow-ups), always provide the
number as a reference.
Q333: “I recently purchased a micro RC aircraft that is powered
by a pair of electric motors. Instead of steering this plane with a
rudder or ailerons, it is controlled by varying the speeds of each
motor. I believe this is referred to as ‘differential motor steering.’
I was wondering if this same concept might be applied to larger
size electric powered aircraft.”
A333: In the November 2007 column I wrote about multiplebrushless-
motor operation and the fact that each motor requires a
separate brushless ESC. The problem, as I pointed out, is that with
separate ESCs the cost and weight goes up with each added motor.
When we used brushed motors, a single ESC could control all of
them.
But despite the increased cost and weight, there is an
interesting advantage to having separate ESCs: you have the
ability to set up your electric power system for differential motor
steering. By speeding up one motor vs. the other (in a twin
02sig3.QXD 12/20/07 12:21 PM Page 8990 MODEL AVIATION
Iron-on covering materials’ weight can be
critical to certain models. A feature about
this subject is planned for MA, but in the
meantime Bob offers suggestions.
On a Polk’s Tracker III the CH 6 knob must be positioned for mid servo range. A
reference mark is made at that position. (The X-Acto knife points to it.) All three mixes
are assigned to switch C, which must be turned on (up).
A dual-landing-wheel Scale-model application required separate axles. The two wires
were wrapped with soft copper wire and silver-soldered together.
Assembling wire pieces for special landinggear
applications is best done with silver
solder and flux known as Stay-Brite.
configuration), the model can be steered on
the ground and, to a degree, in the air as if
it had articulated rudder(s).
The model I showed in the November
column was my new Burnelli CBY-3
“Loadmaster” lifting-body transport. By
the time you read this it should have been
featured in a construction article in Air
Age’s January 2008 Backyard Flyer
magazine. To keep the design simple I did
not resort to rudder control (only ailerons
and elevator).
Hooking up twin operating rudders can
pose problems. Unfortunately this
particular lifting-body design proved to be
hard to grip when hand launching the
model. Without rudders there was no way
to steer a straight course on the ground for
a takeoff.
I did some checking and took an idea
from my flying partner, Tom (Mr. NEAT
Fair) Hunt. This scheme is generally not
mentioned in RC-system handbooks or
operating manuals. To do this job right
you will need a programmable RC
transmitter along with a six-channelcapable
receiver. A five-channel receiver
will not fit this application and, in fact,
could be dangerous depending on where
your retract switch was set.
(Editor’s note: Channel 5 isn’t
proportional on all radio systems and/or
its switch can’t be deactivated.)
To make this control scheme work you
need a separate ESC operating each of the
two brushless motors (which should
always be the case). On the aircraft side,
the ESC for the left-side motor (looking
from the rear of the model forward) goes
to receiver port No. 3. The ESC for the
right-side motor goes to receiver port No.
6.
I used a Polk’s Tracker III transmitter.
First, I went to PMIX 1 and set CH 3 as
Master, CH 6 as Slave, and the mix at
+100%. Second, I went to PMIX 2 and set
CH 4 as Master, CH 3 as Slave, and the
02sig3.QXD 12/20/07 12:29 PM Page 90mix at +30%. Third, I went to PMIX 3 and
set CH 4 as Master and CH 6 as Slave
with the mix at –30%.
It is most important that you limit
yourself to 30% on PMIX 2 and 3, and
make sure that one is positive while the
other is negative. If the motors work
opposite to each other, reverse the + and –
or swap channels 3 and 6 at the receiver.
Now for the tricky part. The Tracker III
transmitter’s CH 6 control function is
managed by a rotary knob. That channel
must be preset to the neutral position. To
do this, plug a servo with a long output
arm into your receiver’s aileron or elevator
channel function and set the transmitter
trim lever for that channel to neutral. (And
make sure no memory trim was being used
on that channel.) Make sure the servo
output arm is at 90° to the servo case.
Plug that servo into your receiver’s CH
6 port and rotate the knob for the same
midrange position, where the servo arm is
again at 90° to the case. After doing this I
made a mark with a pen next to the knob
92 MODEL AVIATION
Celebrating30Years!
- SECURE SHOPPING WITH OUR ONLINE CATALOG -
www.fiberglassspecialtiesinc.com
[email protected]
Phone (479) 359-2429 Fax (479) 359-2259
Hours: Monday - Friday 9 to 5 CST
15715 Ashmore Dr., Garfield, Arkansas 72732
LARGEST COLLECTION OF
EPOXY GLASS COWLS &
WHEEL PANTS IN THE WORLD!
Download a Free Catalog from the World's
Largest Manufacturer of Model Airplane
Cowls, Wheelpants & Accessories.
to make sure it wasn’t accidentally rotated
to another position. You might also
consider placing tape over that control
knob.
The other thing you must do is go to
the Switch Assign portion of the
transmitter menu and assign PMIX 1,
PMIX 2, and PMIX 3 to Switch C. With
that switch in the upper position (No. 1),
all three mixes will be activated. Don’t
touch that switch again!
Having done all this, your transmitter
throttle control stick will run both motors
together at speeds from idle to full. This is
what you will normally use in flight.
Rocking the transmitter rudder control
stick from side to side will vary the
motors’ speeds. If you apply right rudder,
the motor on the left side will run faster
than the one on the right. If you apply left
rudder, control will do the reverse. That’s
the differential. It allows for steering on
the ground as if you had articulated
(moving) rudders on your aircraft, but with
much less work.
These instructions apply to a Polk’s
Tracker III transmitter, but other brands of
systems should work in roughly the same
manner. You might want to contact other
manufacturers for the details.
The success I had with this differential
steering is going to prompt me to design
many more electric-powered twins.
Q334: “I have an application for iron-on
covering where the weight of the material
may be critical. Is there any information
available that compares the weights of the
various iron-on covering material now on
the market?”
A334: I thought this subject had been
covered in the past. However, after an
extensive search I realized that much has
changed through the years and some older
products are gone and newer ones have
taken their place.
The entire topic of iron-on covering
material, the weight, intended application,
and application technique needs a
considerable update. This was discussed
with AMA’s Publications Department, and
a feature article is planned on this subject.
In the meantime I came up with an
interesting weight-comparison table that is
presented on the Internet.
In addition there are two excellent
books by Faye Stilley: Covering R/C
Airplanes, volumes 1 and 2, published by
Air Age Media (which publishes Model
Airplane News). Faye is an iron-oncovering
application master. The books are
available from the AMA Supply and
Service or go to the AMA Web site and
select “Shop AMA,” “Browse our
Catalog,” “Books and DVDs,” and then
scroll to these two volumes.
02sig3.QXD 12/20/07 12:21 PM Page 92Q335: “I’m having trouble soldering such
things as landing gear wire and braces
using conventional solder. I understand
there may be a better type solder available
to do this kind of job. Can you help me?”
A335: Many modelers try to use the more
common rosin core (electrical) solder for
this kind of application. For joining wire,
as is the case with landing gear, you should
be using silver solder. This type of solder
has been on the market for years, usually
under the trade name Stay-Brite. It is
manufactured by The Harris Products
Group.
I’m sure this product has many
distributors across the country. One is
Riverside Machine Shop Inc. of DeQueen,
Arkansas. The silver solder and special
liquid flux are supplied as a kit. One will
last for quite a while and costs $12 plus
shipping.
When using this solder, make sure you
have enough heat. I use a 50-watt iron with
a good-size chisel tip. For most applications
you will be joining several lengths of wire.
Before soldering I wrap the wire with bare
copper wire. You can easily pull some
strands of that from common zip cord.
(Editor’s note: Don’t forget to
thoroughly clean all the metal with Emery
paper.)
Apply the liquid flux and then bring
your hot iron and silver solder to the
intended joint. The shiny flow of solder is
a sign that you’ll have a strong joint. A
photo shows a recent landing-gear strut I
assembled with silver solder.
Don’t use this solder or flux on any
electrical wiring; it is highly corrosive. In
fact, when you are finished making a wire
joint it’s a good idea to clean the soldered
area with denatured alcohol and an old
toothbrush. This will remove any flux
residue. MA
Sources:
AMA
(765) 287-1256
www.modelaircraft.org
Weights of Covering Materials
http://webpages.charter.net/rcfu/HelpsHint
s/IOCWeight.html
Riverside Machine Shop Inc.
(870) 642-7643
www.riversidemachine.net/item17134.ctlg
The Harris Products Group
(800) 733-4043
www.harrisproductsgroup.com
Edition: Model Aviation - 2008/02
Page Numbers: 89,90,92,94
Left
ESC
Right
ESC
Differential motor steering
February 2008 89
? Frequently Asked Questions Bob Aberle | [email protected]
Also included in this column:
• Covering-material weight
• Silver solder
Above: Bob’s fantasy scale Burnelli CBY-3. The prototype model did
not employ movable twin rudders, so it was impossible to steer on
the ground. Differential motor steering solved the problem.
Left: Bob’s CBY-3 used two AXi 2204/54 brushless outrunners.
Having separate ESCs allows you to use differential motor steering.
Below: This shows how two brushless motors and separate
brushless ESCs can provide differential motor steering.
Differential
Motor Steering
Left
Motor
Right
Motor
Receiver
Transmitter
CH3 CH6
Left
Rudder
Right
Motor
Speeds Up
Airplane
Goes Left
PLEASE WRITE IN with your questions, since that is the only
way we can keep this column format going. When referring to
already published Q/As (for follow-ups), always provide the
number as a reference.
Q333: “I recently purchased a micro RC aircraft that is powered
by a pair of electric motors. Instead of steering this plane with a
rudder or ailerons, it is controlled by varying the speeds of each
motor. I believe this is referred to as ‘differential motor steering.’
I was wondering if this same concept might be applied to larger
size electric powered aircraft.”
A333: In the November 2007 column I wrote about multiplebrushless-
motor operation and the fact that each motor requires a
separate brushless ESC. The problem, as I pointed out, is that with
separate ESCs the cost and weight goes up with each added motor.
When we used brushed motors, a single ESC could control all of
them.
But despite the increased cost and weight, there is an
interesting advantage to having separate ESCs: you have the
ability to set up your electric power system for differential motor
steering. By speeding up one motor vs. the other (in a twin
02sig3.QXD 12/20/07 12:21 PM Page 8990 MODEL AVIATION
Iron-on covering materials’ weight can be
critical to certain models. A feature about
this subject is planned for MA, but in the
meantime Bob offers suggestions.
On a Polk’s Tracker III the CH 6 knob must be positioned for mid servo range. A
reference mark is made at that position. (The X-Acto knife points to it.) All three mixes
are assigned to switch C, which must be turned on (up).
A dual-landing-wheel Scale-model application required separate axles. The two wires
were wrapped with soft copper wire and silver-soldered together.
Assembling wire pieces for special landinggear
applications is best done with silver
solder and flux known as Stay-Brite.
configuration), the model can be steered on
the ground and, to a degree, in the air as if
it had articulated rudder(s).
The model I showed in the November
column was my new Burnelli CBY-3
“Loadmaster” lifting-body transport. By
the time you read this it should have been
featured in a construction article in Air
Age’s January 2008 Backyard Flyer
magazine. To keep the design simple I did
not resort to rudder control (only ailerons
and elevator).
Hooking up twin operating rudders can
pose problems. Unfortunately this
particular lifting-body design proved to be
hard to grip when hand launching the
model. Without rudders there was no way
to steer a straight course on the ground for
a takeoff.
I did some checking and took an idea
from my flying partner, Tom (Mr. NEAT
Fair) Hunt. This scheme is generally not
mentioned in RC-system handbooks or
operating manuals. To do this job right
you will need a programmable RC
transmitter along with a six-channelcapable
receiver. A five-channel receiver
will not fit this application and, in fact,
could be dangerous depending on where
your retract switch was set.
(Editor’s note: Channel 5 isn’t
proportional on all radio systems and/or
its switch can’t be deactivated.)
To make this control scheme work you
need a separate ESC operating each of the
two brushless motors (which should
always be the case). On the aircraft side,
the ESC for the left-side motor (looking
from the rear of the model forward) goes
to receiver port No. 3. The ESC for the
right-side motor goes to receiver port No.
6.
I used a Polk’s Tracker III transmitter.
First, I went to PMIX 1 and set CH 3 as
Master, CH 6 as Slave, and the mix at
+100%. Second, I went to PMIX 2 and set
CH 4 as Master, CH 3 as Slave, and the
02sig3.QXD 12/20/07 12:29 PM Page 90mix at +30%. Third, I went to PMIX 3 and
set CH 4 as Master and CH 6 as Slave
with the mix at –30%.
It is most important that you limit
yourself to 30% on PMIX 2 and 3, and
make sure that one is positive while the
other is negative. If the motors work
opposite to each other, reverse the + and –
or swap channels 3 and 6 at the receiver.
Now for the tricky part. The Tracker III
transmitter’s CH 6 control function is
managed by a rotary knob. That channel
must be preset to the neutral position. To
do this, plug a servo with a long output
arm into your receiver’s aileron or elevator
channel function and set the transmitter
trim lever for that channel to neutral. (And
make sure no memory trim was being used
on that channel.) Make sure the servo
output arm is at 90° to the servo case.
Plug that servo into your receiver’s CH
6 port and rotate the knob for the same
midrange position, where the servo arm is
again at 90° to the case. After doing this I
made a mark with a pen next to the knob
92 MODEL AVIATION
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to make sure it wasn’t accidentally rotated
to another position. You might also
consider placing tape over that control
knob.
The other thing you must do is go to
the Switch Assign portion of the
transmitter menu and assign PMIX 1,
PMIX 2, and PMIX 3 to Switch C. With
that switch in the upper position (No. 1),
all three mixes will be activated. Don’t
touch that switch again!
Having done all this, your transmitter
throttle control stick will run both motors
together at speeds from idle to full. This is
what you will normally use in flight.
Rocking the transmitter rudder control
stick from side to side will vary the
motors’ speeds. If you apply right rudder,
the motor on the left side will run faster
than the one on the right. If you apply left
rudder, control will do the reverse. That’s
the differential. It allows for steering on
the ground as if you had articulated
(moving) rudders on your aircraft, but with
much less work.
These instructions apply to a Polk’s
Tracker III transmitter, but other brands of
systems should work in roughly the same
manner. You might want to contact other
manufacturers for the details.
The success I had with this differential
steering is going to prompt me to design
many more electric-powered twins.
Q334: “I have an application for iron-on
covering where the weight of the material
may be critical. Is there any information
available that compares the weights of the
various iron-on covering material now on
the market?”
A334: I thought this subject had been
covered in the past. However, after an
extensive search I realized that much has
changed through the years and some older
products are gone and newer ones have
taken their place.
The entire topic of iron-on covering
material, the weight, intended application,
and application technique needs a
considerable update. This was discussed
with AMA’s Publications Department, and
a feature article is planned on this subject.
In the meantime I came up with an
interesting weight-comparison table that is
presented on the Internet.
In addition there are two excellent
books by Faye Stilley: Covering R/C
Airplanes, volumes 1 and 2, published by
Air Age Media (which publishes Model
Airplane News). Faye is an iron-oncovering
application master. The books are
available from the AMA Supply and
Service or go to the AMA Web site and
select “Shop AMA,” “Browse our
Catalog,” “Books and DVDs,” and then
scroll to these two volumes.
02sig3.QXD 12/20/07 12:21 PM Page 92Q335: “I’m having trouble soldering such
things as landing gear wire and braces
using conventional solder. I understand
there may be a better type solder available
to do this kind of job. Can you help me?”
A335: Many modelers try to use the more
common rosin core (electrical) solder for
this kind of application. For joining wire,
as is the case with landing gear, you should
be using silver solder. This type of solder
has been on the market for years, usually
under the trade name Stay-Brite. It is
manufactured by The Harris Products
Group.
I’m sure this product has many
distributors across the country. One is
Riverside Machine Shop Inc. of DeQueen,
Arkansas. The silver solder and special
liquid flux are supplied as a kit. One will
last for quite a while and costs $12 plus
shipping.
When using this solder, make sure you
have enough heat. I use a 50-watt iron with
a good-size chisel tip. For most applications
you will be joining several lengths of wire.
Before soldering I wrap the wire with bare
copper wire. You can easily pull some
strands of that from common zip cord.
(Editor’s note: Don’t forget to
thoroughly clean all the metal with Emery
paper.)
Apply the liquid flux and then bring
your hot iron and silver solder to the
intended joint. The shiny flow of solder is
a sign that you’ll have a strong joint. A
photo shows a recent landing-gear strut I
assembled with silver solder.
Don’t use this solder or flux on any
electrical wiring; it is highly corrosive. In
fact, when you are finished making a wire
joint it’s a good idea to clean the soldered
area with denatured alcohol and an old
toothbrush. This will remove any flux
residue. MA
Sources:
AMA
(765) 287-1256
www.modelaircraft.org
Weights of Covering Materials
http://webpages.charter.net/rcfu/HelpsHint
s/IOCWeight.html
Riverside Machine Shop Inc.
(870) 642-7643
www.riversidemachine.net/item17134.ctlg
The Harris Products Group
(800) 733-4043
www.harrisproductsgroup.com
