February 1955 Popular Electronics
[Table of Contents]People old and young enjoy waxing nostalgic about
and learning some of the history of early electronics. Popular Electronics was published from October 1954 through April 1985. All copyrights are hereby acknowledged.
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who has been in aeromodeling for more than a decade or so is familiar
with the name William (Bill) Winter. Bill has been in the model airplane
realm for longer than a lot of us have been alive and is one of the
true pioneers of the sport. He has served as editor for a couple aircraft
modeling magazines, and has written countless articles both for the
magazines he edited and for other special interest magazines. When Popular
Electronics came on the scene in the mid 1950s, Bill was editor of
Model Airplane News
. Radio control was beginning to mature
from its infant state when only hobbyists with an intimate knowledge
of electronics were able to participate. Oliver Read, editor of Popular
Electronics, tapped Bill's ample knowledge and skill to craft quite
a few articles for his own magazine. This one, Radio Control Installations,
appeared in the February 1955 issue. As always when reading this type
of vintage material, it is amazing how much innovation has occurred
between then and today in the fields of electronics, materials, and
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Radio Control Installations
by William Winter,
Editor, "Model Airplane News"
the oddities of the radio control hobby is the persistent underestimation,
even by some manufacturers, of the problems of installing the airborne
equipment. Most directions stop with a wiring diagram and the "dope"
on tuning. It is no wonder then that the beginner's first R/C installation
is a rat's nest of wires, or that the radioman's first model often is
torn up by loose batteries and catapulting equipment on the first really
A shipshape installation is accessible, removable,
facilitates proper functioning of the radio, protects the equipment,
and, just as important, protects the airplane from the equipment in
a crack-up. If these requirements are not met, the best radio in the
world is rendered unreliable.
this sounds like making a mountain out of a molehill, consider the unnecessary
damage that happens to a relay when the receiver bangs around inside
a cabin. The heavy coil may deform the frame, causing delicate pivots
to bind. This will result in skipping and sticking, eventually causing
a bad crack-up or a fly-away. This is just one of the ways a poor installation
endangers the equipment.
Let's take the requirements in the
order given. First is accessibility. This, like Sergeant Friday, covers
a lot of territory. Just because the frequency trimmer can be reached
with a tuning wand doesn't mean that the receiver is accessible. A slug
tuner which requires tightening of a lock nut so that vibration will
not cause detuning, isn't accessible when the lock nut is under the
receiver chassis! Or, you may want to reach the relay to clean a contact,
or to adjust spring tension, or reset a contact. Battery voltages often
must be read on the field, or batteries may have to be replaced, or
the escapement or servo checked. Anything that requires observation
or adjustment should be readily accessible.
be removable. Maintenance alone requires that all principal parts of
the radio system be removable, that is, battery packs, receiver, and
actuator. Exhaust smoke from the engine and dust on the field penetrate
cabins, eventually causing leakages of capacitors, etc. It certainly
is worthwhile to keep the receiver chassis clean. Soldered joints need
regular inspection - components may have been pushed out of place, perhaps
to the point of shorting out. Tubes may be loose, a burr might have
developed on the revolving arm of the escapement, or the armature of
a servo motor may require cleaning. The radio model is, after all, a
real aircraft and, like a real aircraft, requires periodic checks. It
is not uncommon for an active hobbyist to log a hundred or more flights
a year. If the equipment is not inspected regularly, the model will
become a casualty before that many flights can be racked up.
well the receiver does its job depends on the neatness of the installation
and the provision included against the ill effects of engine vibration
upon the relay. The beginner tends to place batteries, receiver, and
escapement wherever convenient, then to run wires, like as not through
space, point to point. Wires can be grouped or cabled. Those wires that
connect the switch, potentiometer, jack, sockets, and other stationary
components that remain in the plane, regardless of the removability
of the receiver, batteries, or actuators, should be fastened to the
structure, led along the corners between walls and floor, or by bulkheads
(crosswise partitions) and walls.
The stationary wiring can
be constricted into a very small area by a compact arrangement of the
permanently installed fixtures. By using miniature socket-type plugs,
the receiver can be provided with a plug-in cable, and the battery pack
with another. Either or both can be removed by slipping out the plug.
Standardize your receiver cable connections to make receivers interchangeable
between ships. One big advantage of this practice is that friends can
cooperate by sharing receivers when necessary, provided the hook-ups
are standard. On the five-pin plug the following connections are suggested:
pin 1, "A+"; pin 2, "B+"; pin 3, common minus; pins 4 and 5, relay.
Damping of vibration is accomplished by a variety of shock mounting
systems, the two most common ones being a rubber band suspension of
the receiver in a horizontal position, or the placement of the receiver
upon a block of foam rubber, either vertically or horizontally. If vertically
mounted, the receiver has an infinitely greater immunity to crack-up
damage. Indeed, it is possible to destroy the airplane without detuning
the receiver or even knocking the relay out of adjustment, when vertical
mounting is used. Heavier and larger receivers sometimes rest upon two
blocks of sponge, one at either end, or at either side, as the case
may be. The rubber is faced with 1/16-inch thick plywood (using rubber
cement) and the chassis ends or mounting lugs are attached to the plywood
with small wood screws.
Example of battery installation in the
belly of an airplane under the hardwood floor. The forward box contains
a hearing-aid "B" battery, the rear compartment contains the batteries
for the receiver filaments (1 1/2 volts) and the escapement requiring
Good shock absorption is essential to good
relay operation. The writer has seen cases where a 10,000-ohm sensitive
relay considered shock proof would not pull in when mounted firmly on
wood with a powerful engine shaking the airplane. Contact pressures
may not be sufficient to hold a rudder in one position as the plane
shudders out of a dive. Probably the manufacturers themselves don't
know what happens to a relay armature during repeated signaling in the
presence of a severe harmonic vibration, as only modelers seem to create
it. If a good installation is able to employ the means of damping vibration
to provide crash protection as well, you are ahead of the game.
but not least, is the protection of the airplane from loose equipment.
This means that all heavy objects, notably the batteries and the receiver,
should not be permitted to gather momentum before coming to rest against
a bulkhead. Batteries should always rest snugly against a bulkhead,
This bulkhead should be strengthened across the grain with cross members
or plywood to prevent splitting. Its ends, or joints with the floor
or walls, should be butted against forward movement that would tear
out the joints. Batteries should not be fastened down upon flooring,
and never held loosely in place. A vertically-mounted receiver that
rests against a firm bulkhead, with appropriate strengthening against
splitting and movement, causes little or no structural damage and is
itself unhurt by hard knocks.
which depend on rubber-bands from the four corners of the chassis may,
on a short stop, penetrate a ply bulkhead with well imagined results
to electronic equipment. A tether cord attached to the chassis and anchored
behind the chassis to some strong point, prevents the receiver from
traveling too far, although the back travel, like recoil of a gun, should
be similarly damped for safety. Even though the horizontal mounting
may hold in a crash, it is likely that the Sigma 4F-type relay will
be deformed. Tubes will pop out, and everything that isn't tied down,
like chokes, quench coils, and capacitors, will move out of position.
Escapements and push rods take special handling to prevent crash
damage. Escapements that simply are cemented against a balsa partition
will tumble into the cabin when the plane bangs onto its nose. A pushrod
may take off like a javelin, pulling loose the linkage assembly and
One method for mounting a receiver horizontally is shown here. Batteries
and the socket for receiver cable are well forward.
R/C model plane with the receiver mounted horizontally. The batteries
are in the nose, mounted on a piece of plywood and inserted through
the floor for easy accessibility.
Removable box containing batteries, receiver, and actuator. This
allows for easy removal from a plane and interchange between planes.
With such considerations in mind we can tackle the four typical installations
given in the illustrations. First is the old fashioned rubber-band mounted
receiver, accessible in this case by means of two large access doors
in the sides of the ship. A is the plywood bulkhead; B is a thick sheet-balsa
floor or a thin plywood floor. The batteries are stacked against the
bulkhead or laid flat on the floor with their front edges flush against
the bulkhead. The switches, potentiometer, jack, etc., line up along
the lower edge of the cabin on the left side, facing a right handed
launcher. (This is more or less standard, so the arrangement of accessories,
switches, etc., will not be detailed in subsequent examples.)
The receiver is suspended by rubber bands (two light bands to each
corner stretched to about one-third their limit). C is a tether cord
attached to the rear wing hold-down dowel, D. F is a small chassis mounting
two sockets, one to accept the battery cable lead, the other the receiver
cable. Note the structural cross members, G, that reinforce bulkhead
A. The section forward of this reinforcement is double skinned on each
side, with the inner, thicker skin-3/16 or 1/4-inch thick sheet balsa,
butting against bulkhead A.
A popular mounting method is to
have both receiver and batteries vertical. This provides excellent accessibility
to the radio from the open top of the cabin, and to the battery pack
from the removable top of the nose section. A is a 1/4-inch sheet-balsa
bulkhead; B is either a 1/8-inch plywood or a 1/4-inch sheet-balsa bulkhead,
whose grain runs across ship. Note that the impact of the batteries
is against this bulkhead; that of the receiver, partly snubbed by foam
rubber, is transmitted through A. The impact of the snug fitting batteries
is transmitted to the key bulkhead B. Switches, potentiometer, and jack
line up as before, well out of the way should the receiver swing from
side to side. C is a foam rubber block, against which the receiver is
anchored by small rubber bands. The tension of the bands is just enough
to prevent the receiver from hanging loosely or swinging back and forth
on landing. The battery cable D comes through bulkhead A, and plugs
into a socket on chassis E. The receiver cable plugs into a similar
socket. Note that the escapement is fully accessible.
of the torque rod linkage to the rudder is that the linkage cannot damage
the escapement in a crack-up, whereas the pushrod type transmits a blow
to the escapement assembly. Pushrods and bellcranks also put a dead
weight on the escapement, which can be a handicap when the nose is down.
Pushrods usually require heavier rubber drive for safety and this in
turn makes escapement and performance more critical.
of the vertical-type mounting is also shown. Here, a plywood floor A
extends between bulkheads C and D. Observe that the floor continues
forward of bulkhead B, so that the battery weight can be carried far
enough toward the nose for correct balancing. Battery boxes bolt directly
to the floor, and are accessible by means of a large bottom hatch. The
Acme Products Company makes sturdy battery boxes for all popular battery
combinations including hearing aid "B" batteries. If desired, a large
"B" battery may be dropped into place between bulkheads B and D, with
D then requiring the usual forward structural support. Escapements,
switches, etc., are mounted as before. The large plywood floor is ideal
for anchoring the heavier motor-driven servo-type actuators.
Still another arrangement having very special advantages is the
removable box method. This box contains the batteries, receiver, and
even the servo or escapement. By detaching the linkage from the actuator,
the box can be lifted from the plane without disconnecting a wire. Moreover,
it can be dropped into another plane. It is unnecessary to have an actuator
in every plane with this set-up. The batteries are packed in a forward
compartment in the box; the actuator is mounted at the rear, but in
such a manner that it does not snag the adjacent bulkhead when the box
is lifted out. Switches, potentiometer, jack, etc., have to be on the
bottom of the box, and are reached through holes in the bottom of the
ship when the box is in place. In fact, the toggle switch handle extends
from the bottom. Usually more confined than a wide open cabin, the box
requires that some receivers be beam mounted, that is, placed upon two
blocks of foam rubber at either end, or along the sides.
is not intended that these examples be followed to the exclusion of
the reader's own ideas. Rather, it is hoped that this resume of a few
of the better kinds of installations will assist the newcomer in the
successful operation of his new plane.
It would be well to draw
upon these comments in sketching in any installation upon the plan that
comes with your airplane kit - before cementing a piece of wood. Few
kits detail installations, merely saying, put the batteries here, etc.
Nor are they always wise in the location of some items such as an escapement.
The average modeler is a great individualist, especially in radio control.
So don't be afraid to "gild the lily."