Pete O Shea
Apr 01, 1997, 01:00 AM
<h4><font size="4">April 1997: Interference: What to Do When the Bug Bites You</font> </h4>
<p>This month I'm covering a topic that everyone experiences at one time or another: radio
interference. Since our electric powerplants produce broadband radio noise as well
as mechanical work and heat, we experience this phenomenon even more often than glow
fliers. What's interference? you ask. It's when something causes an interruption or
cessation of the control link between transmitter and airplane. In my case, flying
an airplane is challenging enough without a loss of control, so I get very unhappy when a
glitch causes the airplane to jump. </p>
<p>Interference is usually noticed as a momentary glitch in the airplane's flight path,
and is caused by one or more servos receiving incorrect signals. It also can be a
temporary rapid change in the throttle setting. In more severe cases, the
interference can be continuous and cause the plane to be unflyable. </p>
<hr>
<p>Like many things, the topic of reducing interference can be divided into three
categories: </p>
<p>1. <font color="#FF0000">Reduce the amount of generated noise</font> </p>
<p>a. The first thing to try, when experiencing interference, is to reduce the amount of
radio noise generated by the motor. The most common way to reduce noise is to
install capacitors at the motor terminals. The capacitors will effectively short out
the high-frequency noise produced by the motor before the noise travels through the power
system wiring. Use disc ceramic capacitors of about 0.01 microfarad, although this value
is not critical. The capacitors should be rated for a voltage at least twice the
voltage of the nicad battery. These capacitors can be found at any Radio Shack. Put
one capacitor from each motor terminal to the motor case. You may need to drill and
tap a hole in the motor case if it can't be soldered, but be careful that the screw you
install doesn't impede the motion of the armature! This wiring configuration uses the
motor case to shield some of the radio energy and is more effective than putting one
capacitor across the terminals. </p>
<p>b. The next thing to try is to make sure that the motor timing is correct. I
don't want to go into the details of motor timing, but if the motor is too far advanced or
too far retarded, there will be excessive arcing at the brush-commutator interface.
Arcing, besides causing high brush wear, causes much higher amounts of radio energy
to be created. The first early radio transmitters , such as Marconi used, actually
employed a large electric arc to produce a broadband radio signal! You do not want
to reproduce this with your motor. </p>
<p>The quick description of setting the timing for a brushed motor is this: remove the
prop from the motor and run it unloaded with a current meter in the circuit. Adjust
the timing until the unloaded current is a minimum. This is neutral timing.
Advance the timing by rotating the magnets relative to the brushes in the direction
of motor rotation until the current rises by 1/10 of the anticipated operating current.
If, say, you intend to fly the plane propped to a current of 25 amps, and the
no-load neutral-timed current is 2 amps, then the motor should be advanced until the
unloaded current becomes 2 + (0.1*25) = 4.5 amps. </p>
<p>c. If your budget permits, use a brushless motor. The brushless motor, since it
has no brush-commutator interface, produces much less radio noise. </p>
<p>2. <font color="#FF0000">Reduce the coupling of the generated noise into the radio
receiver</font> </p>
<p>a. Move the receiver as far as possible away from the motor and the power system
wiring. This is subject to the constraints of the fuselage size, but remember that
necessity is the mother of invention. Be creative. </p>
<p>b. Twist the power system wiring. About one to two twists per inch (perhaps one
twist per two centimeters) is fine; too many will require more wiring, adding weight.
This will add inductance to the power system wiring, helping to block the flow of
high-frequency energy. </p>
<p>c. Place the receiver antenna at right angles to the power system wiring, if possible. </p>
<p>3. <font color="#FF0000">Use good quality radio components</font> </p>
<p>a. There is really only one type of receiver that should be used for electric flight,
and that is the double-conversion FM receiver. Cheaper AM radio systems are too
prone to interference for use in our demanding radio environment. The choice between
pulse-code modulation (PCM) and pulse-position modulation (PPM) is less critical. PCM is
more tolerant of interference, but at an additional price. </p>
<p>b. Use an opto-isolated speed control. This puts a one-way barrier between the radio
receiver and the power system wiring. Control signals can pass from the radio to the speed
control, but noise cannot travel backwards from the speed control into the receiver.
Opto-isolation cannot coexist with battery-eliminator circuitry (BEC), but it is well
worth it. </p>
<hr>
<h4><font size="4">Exciting New Battery Technology</font> </h4>
<p>I found an interesting article about battery technology in the most recent EE Times
magazine. It was about a conference put together for laptop computer power systems
designers, and described some interesting charge monitoring technologies as well as new
cell chemistries. One that I found interesting was a spin-off of the zinc-air
battery: the zinc-helium battery. In this cell, the helium acts as a gaseous
electrolyte and provides very efficient charge transport. The specifications of the cell
are promising: about 1.8 times greater capacity than nicad cells of the same size. The
replacement of the heavy paste electrolyte with gaseous helium puts the weight at about
0.6 the weight of the typical nicad cell. The internal impedance of the cell is improved
over nicad cells as well. </p>
<p>One significant difference with this new cell chemistry is the charge regime. Under
charge, the cell voltage actually decreases, and the minimum voltage signals the end of
charge. Looks like our peak chargers will need some modification! </p>
<p>This new technology is still under development and commercial cells are not planned for
release until April 1998. For more information, <a href="#April Fools!">click
here.</a></p>
<hr>
<h4><font size="4">KRC Revisited: A Contest</font> </h4>
<p>A few weeks ago I was going through a stack of airplane papers I had lying around, when
I found some pictures taken at last year's KRC Electric Fly. In case you missed it
or live too far away, I thought I'd put in a few from the All-Up, Last-Down contest. </p>
<p align="center"><img src="http://static.rcgroups.com/articles/ezonemag/sporttop/../../images/krclnch1.jpg" width="441" height="253"> </p>
<p>This is about half of the launch line-up for the AULD. The officials are giving
last-minute instructions, pilots are checking that their transmitters and airplanes are on
and armed..... </p>
<p align="center"><img src="http://static.rcgroups.com/articles/ezonemag/sporttop/../../images/krclnch2.jpg" width="423" height="256"> </p>
<p>Here I am a split-second after the mass launch. No, I'm not cringing, I
hand-launch my own plane and I've just given it a great big heave. Note that I've
tossed my v-tail Eclipse into a nice right turn. I managed to recover from it
and continue on to a splendidly mediocre finish. There's always next year. </p>
<p><font color="#FF0000" size="4">And now, the contest</font>. Who is the pilot
sandbagging his launch in the left of the above picture? The first person to <a href="http://rcgroups.com/shared/nospam.php?u=poshea&d=ezonemag.com">email me</a> with the correct answer will win a plans
set from the Ezone. I'll give one hint: he throws his plane with his right arm.
(There, I've eliminated women and left-handed men from the possibilities, it should be
easy.) </p>
<hr>
<h4><font size="4">Work-In-Progress Update</font> </h4>
<p>Notice how, as I got further and further behind, my winter building project became a
winter/spring project? Well, now I'm not even specifying a building
season.....except that I still intend to finish the Yellow Jacket before KRC. I
won't say which year. </p>
<p>I did, however, get one airplane-related item built over the winter. I built a
toy airplane for my son for Christmas, using scrap hardwoods I had around the house.
I put it together in the evenings of the week before Christmas, which makes it the
fastest plane I've ever designed and built. Here's a picture and some data: </p>
<p><img src="http://static.rcgroups.com/articles/ezonemag/sporttop/../../images/woodbank.jpg" align="left" hspace="2" vspace="2" width="412" height="277"><strong>Weight</strong>: 5.5 lbs. </p>
<p><strong>Wing span:</strong> 20 inches </p>
<p><strong>Wing area:</strong> 80 square inches </p>
<p><strong>Wing loading: </strong>158 ounces/square foot </p>
<p><strong>Power:</strong> One flick-power </p>
<p><strong>Airfoil: </strong>TLAR-1 </p>
<p>The fuselage is solid rock maple, from a tree I cut down a few years ago and had drying
in my basement. The wing, tail, tail skid, cowl, and pilot's body are cherry left
over from our house restoration work. The landing gear and propeller are black
walnut, also from our house. I patterned the propeller after a Rev-Up 8x4 I had
laying around. I chickened out slightly from my built-by-hand intentions: the
pilot's head and the wheels are store-bought. Well, <u>you</u> try making a hardwood
sphere at 2 AM a couple of nights before Christmas. Oh, yes, it's also a bank:
the front of the fuselage was laboriously hollowed out, and the pilot lifts and pivots to
reveal the coin/bill slot. To remove the money, the cowl block comes off. The
whole plane is held together with glue and hardwood dowels. I gnawed the dowels to
shape from sticks I picked up around the yard. </p>
<hr>
<p>It's spring! Get something flying, </p>
<p>Pete </p>
<h1 align="center"><a name="April Fools!"><font color="#FF0000">April Fools!</font></a></h1>
<p><font size="2">In case you didn't figure it out, the exciting new battery technology is
an exciting, big April Fool's! So are the gnawed hardwood dowels. Sorry.</font> </p>
<p><a href="http://rcgroups.com/shared/nospam.php?u=poshea&d=ezonemag.com">E-mail</a> the author </p>
<p><a href="/articles/ezonemag/sporttop/petebio.htm">About</a> the author </p>
<p>This column is copyrighted (c) 1997 by Peter O'Shea and may not be reprinted or
retransmitted without proper attribution to the author and the E-Zone.
<p>This month I'm covering a topic that everyone experiences at one time or another: radio
interference. Since our electric powerplants produce broadband radio noise as well
as mechanical work and heat, we experience this phenomenon even more often than glow
fliers. What's interference? you ask. It's when something causes an interruption or
cessation of the control link between transmitter and airplane. In my case, flying
an airplane is challenging enough without a loss of control, so I get very unhappy when a
glitch causes the airplane to jump. </p>
<p>Interference is usually noticed as a momentary glitch in the airplane's flight path,
and is caused by one or more servos receiving incorrect signals. It also can be a
temporary rapid change in the throttle setting. In more severe cases, the
interference can be continuous and cause the plane to be unflyable. </p>
<hr>
<p>Like many things, the topic of reducing interference can be divided into three
categories: </p>
<p>1. <font color="#FF0000">Reduce the amount of generated noise</font> </p>
<p>a. The first thing to try, when experiencing interference, is to reduce the amount of
radio noise generated by the motor. The most common way to reduce noise is to
install capacitors at the motor terminals. The capacitors will effectively short out
the high-frequency noise produced by the motor before the noise travels through the power
system wiring. Use disc ceramic capacitors of about 0.01 microfarad, although this value
is not critical. The capacitors should be rated for a voltage at least twice the
voltage of the nicad battery. These capacitors can be found at any Radio Shack. Put
one capacitor from each motor terminal to the motor case. You may need to drill and
tap a hole in the motor case if it can't be soldered, but be careful that the screw you
install doesn't impede the motion of the armature! This wiring configuration uses the
motor case to shield some of the radio energy and is more effective than putting one
capacitor across the terminals. </p>
<p>b. The next thing to try is to make sure that the motor timing is correct. I
don't want to go into the details of motor timing, but if the motor is too far advanced or
too far retarded, there will be excessive arcing at the brush-commutator interface.
Arcing, besides causing high brush wear, causes much higher amounts of radio energy
to be created. The first early radio transmitters , such as Marconi used, actually
employed a large electric arc to produce a broadband radio signal! You do not want
to reproduce this with your motor. </p>
<p>The quick description of setting the timing for a brushed motor is this: remove the
prop from the motor and run it unloaded with a current meter in the circuit. Adjust
the timing until the unloaded current is a minimum. This is neutral timing.
Advance the timing by rotating the magnets relative to the brushes in the direction
of motor rotation until the current rises by 1/10 of the anticipated operating current.
If, say, you intend to fly the plane propped to a current of 25 amps, and the
no-load neutral-timed current is 2 amps, then the motor should be advanced until the
unloaded current becomes 2 + (0.1*25) = 4.5 amps. </p>
<p>c. If your budget permits, use a brushless motor. The brushless motor, since it
has no brush-commutator interface, produces much less radio noise. </p>
<p>2. <font color="#FF0000">Reduce the coupling of the generated noise into the radio
receiver</font> </p>
<p>a. Move the receiver as far as possible away from the motor and the power system
wiring. This is subject to the constraints of the fuselage size, but remember that
necessity is the mother of invention. Be creative. </p>
<p>b. Twist the power system wiring. About one to two twists per inch (perhaps one
twist per two centimeters) is fine; too many will require more wiring, adding weight.
This will add inductance to the power system wiring, helping to block the flow of
high-frequency energy. </p>
<p>c. Place the receiver antenna at right angles to the power system wiring, if possible. </p>
<p>3. <font color="#FF0000">Use good quality radio components</font> </p>
<p>a. There is really only one type of receiver that should be used for electric flight,
and that is the double-conversion FM receiver. Cheaper AM radio systems are too
prone to interference for use in our demanding radio environment. The choice between
pulse-code modulation (PCM) and pulse-position modulation (PPM) is less critical. PCM is
more tolerant of interference, but at an additional price. </p>
<p>b. Use an opto-isolated speed control. This puts a one-way barrier between the radio
receiver and the power system wiring. Control signals can pass from the radio to the speed
control, but noise cannot travel backwards from the speed control into the receiver.
Opto-isolation cannot coexist with battery-eliminator circuitry (BEC), but it is well
worth it. </p>
<hr>
<h4><font size="4">Exciting New Battery Technology</font> </h4>
<p>I found an interesting article about battery technology in the most recent EE Times
magazine. It was about a conference put together for laptop computer power systems
designers, and described some interesting charge monitoring technologies as well as new
cell chemistries. One that I found interesting was a spin-off of the zinc-air
battery: the zinc-helium battery. In this cell, the helium acts as a gaseous
electrolyte and provides very efficient charge transport. The specifications of the cell
are promising: about 1.8 times greater capacity than nicad cells of the same size. The
replacement of the heavy paste electrolyte with gaseous helium puts the weight at about
0.6 the weight of the typical nicad cell. The internal impedance of the cell is improved
over nicad cells as well. </p>
<p>One significant difference with this new cell chemistry is the charge regime. Under
charge, the cell voltage actually decreases, and the minimum voltage signals the end of
charge. Looks like our peak chargers will need some modification! </p>
<p>This new technology is still under development and commercial cells are not planned for
release until April 1998. For more information, <a href="#April Fools!">click
here.</a></p>
<hr>
<h4><font size="4">KRC Revisited: A Contest</font> </h4>
<p>A few weeks ago I was going through a stack of airplane papers I had lying around, when
I found some pictures taken at last year's KRC Electric Fly. In case you missed it
or live too far away, I thought I'd put in a few from the All-Up, Last-Down contest. </p>
<p align="center"><img src="http://static.rcgroups.com/articles/ezonemag/sporttop/../../images/krclnch1.jpg" width="441" height="253"> </p>
<p>This is about half of the launch line-up for the AULD. The officials are giving
last-minute instructions, pilots are checking that their transmitters and airplanes are on
and armed..... </p>
<p align="center"><img src="http://static.rcgroups.com/articles/ezonemag/sporttop/../../images/krclnch2.jpg" width="423" height="256"> </p>
<p>Here I am a split-second after the mass launch. No, I'm not cringing, I
hand-launch my own plane and I've just given it a great big heave. Note that I've
tossed my v-tail Eclipse into a nice right turn. I managed to recover from it
and continue on to a splendidly mediocre finish. There's always next year. </p>
<p><font color="#FF0000" size="4">And now, the contest</font>. Who is the pilot
sandbagging his launch in the left of the above picture? The first person to <a href="http://rcgroups.com/shared/nospam.php?u=poshea&d=ezonemag.com">email me</a> with the correct answer will win a plans
set from the Ezone. I'll give one hint: he throws his plane with his right arm.
(There, I've eliminated women and left-handed men from the possibilities, it should be
easy.) </p>
<hr>
<h4><font size="4">Work-In-Progress Update</font> </h4>
<p>Notice how, as I got further and further behind, my winter building project became a
winter/spring project? Well, now I'm not even specifying a building
season.....except that I still intend to finish the Yellow Jacket before KRC. I
won't say which year. </p>
<p>I did, however, get one airplane-related item built over the winter. I built a
toy airplane for my son for Christmas, using scrap hardwoods I had around the house.
I put it together in the evenings of the week before Christmas, which makes it the
fastest plane I've ever designed and built. Here's a picture and some data: </p>
<p><img src="http://static.rcgroups.com/articles/ezonemag/sporttop/../../images/woodbank.jpg" align="left" hspace="2" vspace="2" width="412" height="277"><strong>Weight</strong>: 5.5 lbs. </p>
<p><strong>Wing span:</strong> 20 inches </p>
<p><strong>Wing area:</strong> 80 square inches </p>
<p><strong>Wing loading: </strong>158 ounces/square foot </p>
<p><strong>Power:</strong> One flick-power </p>
<p><strong>Airfoil: </strong>TLAR-1 </p>
<p>The fuselage is solid rock maple, from a tree I cut down a few years ago and had drying
in my basement. The wing, tail, tail skid, cowl, and pilot's body are cherry left
over from our house restoration work. The landing gear and propeller are black
walnut, also from our house. I patterned the propeller after a Rev-Up 8x4 I had
laying around. I chickened out slightly from my built-by-hand intentions: the
pilot's head and the wheels are store-bought. Well, <u>you</u> try making a hardwood
sphere at 2 AM a couple of nights before Christmas. Oh, yes, it's also a bank:
the front of the fuselage was laboriously hollowed out, and the pilot lifts and pivots to
reveal the coin/bill slot. To remove the money, the cowl block comes off. The
whole plane is held together with glue and hardwood dowels. I gnawed the dowels to
shape from sticks I picked up around the yard. </p>
<hr>
<p>It's spring! Get something flying, </p>
<p>Pete </p>
<h1 align="center"><a name="April Fools!"><font color="#FF0000">April Fools!</font></a></h1>
<p><font size="2">In case you didn't figure it out, the exciting new battery technology is
an exciting, big April Fool's! So are the gnawed hardwood dowels. Sorry.</font> </p>
<p><a href="http://rcgroups.com/shared/nospam.php?u=poshea&d=ezonemag.com">E-mail</a> the author </p>
<p><a href="/articles/ezonemag/sporttop/petebio.htm">About</a> the author </p>
<p>This column is copyrighted (c) 1997 by Peter O'Shea and may not be reprinted or
retransmitted without proper attribution to the author and the E-Zone.