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Ever since radio control systems have been available commercially,
modelers have gone to sometimes extreme lengths to retrofit them
into items not intended necessarily for R/C. GI Joes have been given
servo-controlled arms to maneuver an R/C released parachute after
being dropped from an R/C airplane or helicopter. Stuffed animals
and dolls have been fitted with motors and controls to make them
walk and move their arms. Cheap Styrofoam free flight gliders from
the toy department of Walmart have had 2- or 3-channel R/C airborne
systems installed to turn the $10 models into respectable thermaling
machines. You can buy micro R/C systems and motor propulsion for
installing on paper airplanes nowadays. This article reports on
an effort to convert free running model cars into radio controlled
vehicles - back when R/C systems were anything but small and light-weight.
How to add Radio Controls to Your Scale Model Auto
Howard McEntee
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Here's what happened when we presented Howard McEntee
with one of ITC's Mercer auto kits ... he soon had a remotely-controlled
radio-operated car!
Staff members were so impressed by the Raceabout's lively
performance and pin-point control we figgered our readers
would like to get in on the fun, too.
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Those realistic scale model autos in plastic kits make fine radio
control subjects. Our R/C installation is easy to duplicate. To
get a good turn of speed, a larger motor now drives our car; proportional
control permits precise steering for obstacle races and model "gym-kana's".
How could a dyed-in-the-wool R/Cer look at a speedster like ITC's
1911 Mercer Raceabout without getting ideas? (This comes with a
pre-set control unit that steers it, flashes lights and switches
the drive motor.) The ITC "gear box" was set aside, its .place taken
by simple friction drive on one rear wheel, using a much larger
motor than supplied in the kit. Otherwise, car was built about as
described in ITC's instruction book.
Our assembly work started with Step 7. To beef up the two steering
knuckles (parts 40 and 43) 13/16" lengths of 9/32" OD brass tubing
were slotted at one end to slide over vertical portions of knuckles,
unslotted portion acts as a new stub axle. Original axles are 1/4"
dia. so tubing is a snug fit. Smear axle and tubing inside with
plastic cement, slide tube in place, add plastic spacer (cut from
unused kit parts) and bend slotted tube tips around knuckles, cementing
brass well. Aurora cement sets rapidly, but takes time to really
harden ... give it all it needs. Complete front axle assembly per
instructions, cement to front springs.
Drill out front wheels to fit enlarged axles. We did this with
a letter J drill, then ran a letter K through. Plastic drills cleanly
if you go slow. - Drill a little, then withdraw drill to clean off
chips and give plastic time to cool.
Rear wheels must turn freely so a new axle of 1/8" music wire
was made. To give it rigidity, an "axle housing" of 1/8" ID brass
tubing is run through plastic shaft hangers under car; this 5 3/4"
long tubing must be well cemented. The pillow blocks (part 65) were
not used, but the axles were cemented to rear springs with scrap
plastic fillers. Also, 1/4" dia. pieces of red plastic "tree" clipped
off and cemented against springs and axle supports beef-up assembly.
Rear wheels' square hole is opened up with a #30 drill for the new
shaft. To the 7 5/8" axle cement a brass washer at one end. Axle
and wheels are held via model plane landing gear wheel collar (with
setscrew) at other end.
 Our
substitute motor, G.M. Hobbies' Super-Monoperm, drives right rear
wheel by friction. It must have a pivoted mounting so a spring will
press it against the wheel. The broad brass "U" pivot attaches to
motor base by 2-56 bolts. A sturdy aluminum or brass "axle" supports
assembly; it bolts at one end to car's plastic underside, is braced
at outer end by aluminum strip cemented to right rear fender. Holes
in area allow cement to really bind tight. File rear spring on this
side to clear motor mount. Fit these parts so none snag rear wheel
or its brake drum, spacing must be close.
Motor has a short 3/32"-dia shaft which is extended and enlarged
in diameter. Allow enough room between tubing and motor case to
grip shaft with needle-nose pliers ... this to keep heat from soft
plastic motor case. To gain more speed, we later soldered 3/8" length
of 1/8" ID tubing over smaller tube. This holds larger size fuel
tubing which con-tacts the rear wheel.
Lights, horn, pumps and spare tire could be damaged in handling
so don't mount till R/C and drive mechanism is complete. Then add
all the details you desire.
 A
geared-down small motor is required for proportional steering. Our
unit is from Citizen-Ship Actuator kit parts (or C-S type HRH, 2R2H,
1R3H or 3R servos - but no switching circuits are needed). Basically
a double-geared Mighty Midget motor, this is much like servos for
proportional plane steering. We omitted contact strip and switching
discs; you could probably utilize some of these parts to switch
on car lights when wheels turn to extremes. Before motor is fastened
in case, tin stub end of shaft (don't get solder on pinion teeth).
Attach a hook to shaft for centering rubber band; ours is 3/4" length
of 1/16" ID brass tubing, with one end flattened and bent to hook
shape. Heat end red hot then let it cool before you flatten it.
Open hole in case end to clear hook shank, clean inside of tubing
and tin it, install hook after motor is in place. The kit's 30 ohm
resistor soldered across motor's terminals acts as arc suppressor
to keep relay contacts clean. This resistor, somewhat lower than
necessary for our purpose, may be raised to 100 ohms to lessen overall
current drain of servo. As added insurance against commutator sparking
bothering receiver, wire 0.001 mf ceramic capacitor across terminals.
Servo is on ply mount cemented to upper surfaces of front springs
and under side of plastic Rear Gear Box Support.
First the servo was centered (as shown) but later it occurred
to us that if offset to left side of chassis, steering wheel could
be linked to the front wheels - as kit's designers intended. Thus
steering wheel turns as servo swings front wheels - an action that
sure intrigues spectators! Lower end of Metal Steering Rod (part
96) was clipped short since servo and mount are in the way.
A short 1/16" soft iron wire link runs from servo crank (which
projects down toward ground) to hole in plastic tie rod. Four wood
screws hold servo.
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Radio installation with servos and receiver (front &
rear underside).
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Center area of chassis under seats holds receiver, its batteries,
all power switches. All plastic projections here are cut off, 1/8"
ply 2 1/2 x 3 1/2" is fitted to forward half of area. To this fasten
battery case, angles to hold receiver power cable socket and vertical
aluminum strip for rear support of centering rubber. Bolt holds
latter strip and a wire hook to which one end of receiver retaining
rubber band goes - other to hook cemented to chassis. Cement in
1/4" foam rubber to protect receiver from jolts - like when you
goof and ram car into a table leg or wall!
All switches mount on 1/8" ply strip 5 x 1 1/8 ", cemented inside
chassis on left side. Rather large receiver cells are used since
there is no need to skimp on size or weight; E93 Eveready alkaline
dry cells should give at least 100 hours of service! Average receiver
current drain is about 30-ma (5-ma with no tone, 60-ma with tone
on).
We had intended to have a superhet in the car; a sharply selective
receiver would allow several vehicles to run at once on the 27 mc
R/C spot frequencies. CG's Jupiter superhet worked fine - until
the servo was turned on. Much time was spent trying to eliminate
servo motor "electrical noise", but to no avail. While the servo
motor made the receiver unhappy, drive motor knocked it out completely!
It might be possible to use a superhet with careful shielding of
all leads and perhaps RF chokes on the offending motors, but it
didn't look like a job the newer RK'er could handle, so a CG Saturn
was plugged in - and our troubles ended. This receiver comes with
plug on power cable and socket connections as shown.
It was our intention to run antenna under fenders out of sight;
this worked up to 30' range. Farther from transmitter dead spots
were encountered when car turned in certain positions relative to
the transmitter. A wire all around car, under fenders and chassis,
didn't help much. So - while original Mercer Raceabout had no radio
antenna, ours does! It's a 16" length of 1/32" music wire raked
rearward along right rear fender; small spring fastener at lower
end allows easy removal. Antenna which permits 70' reliable operating
range could be shorter if you don't want to run the car that far
away.
The same cells are used for drive and steering motors. Since
average current drain when running straight ahead on a smooth surface
is 425-ma, rechargeable cells seemed the answer so four nickel-cad
units are carried under the rear deck. Four 1 AH cells taped into
a black cylinder are button-style Eveready N4OT's. The "T" means
they have solder tabs which makes for easy connections. Since cells
never require servicing they may be soldered into circuit. To make
charging easy install 2-pin connector in an inconspicuous spot so
charger may be connected without removal of rear deck. Cell pack
is kept from rattling by foam rubber cemented in car "fuel tank".
Tank and rear deck snap firmly into place, may be removed any time.
N4OT cells, new to Eveready line, may not be widely available, though
any distributor can obtain them for you. We did quite a bit of car
testing with four Eveready N52 cells, long thin cylinders of pen
cell diameter about twice as long; they are rated at 900-maH capacity.
Lower in cost they may be easier to get. Stocked by mail order radio
houses such as Lafayette, they also have solder tabs. N52 has less
capacity and it is not intended for such heavy duty as the N4OT.
This completes the car, except for such plastic scale details
you may want to add and, of course, coloring.
Now about the transmitter? Short range and average power are
all we need, so let's employ one of the all-transistor transmitters.
We picked Babcock's BCT-16 (though tiny, this has ample power to
operate model planes at standard flight distances).
 For
proportional operation we need a pulser, again transistors do the
job - via a C&S Model CS-504 Pulsi-Tran. The BCT-16 comes with
a keying button in case front, but has no external on-off switch.
Actually, a switch inside changes output from keyed CW to keyed
CW and tone. When this switch is in position #1, no current flows
unless key is depressed. This transmitter comes with a red plug
in its side; an accessory is a green plug - when latter is in use,
and internal switch in position #2, transmitter sends out constant
CW signal, and tone is keyed on and off. In view of electrical noise
of two motors in car, we feel latter mode of operation preferable
and advise use of green plug. (You can make one using connections
shown.)
With green plug, current drain on 9-volt battery is constant
so a larger battery than Eveready #216 which fits inside case is
dictated. Two of these may be paralleled, or you can tape a larger
#246 battery to case bottom as we did. We have a push-pull wire
coming out case side so transmitter internal switch can be moved
to "off" #1 position when not in use. (We hear later BCT-16 models
will have external on-off switch, also room for a #246 battery inside.
To make a single handy unit, we attached C&S Pulsi-Tran to
BCT-16 case front after removing key switch. Two leads from pulser
connect in place of key.
What about operation? We suggest you keep car speed low till
you get knack of steering. To do this, use only 3/32" ID brass tubing
on drive motor shaft, and very thin rubber or plastic tubing over
it (fuel tubing works fine). Later you can speed up the auto by
rubber or plastic of 1/4" diameter or more - this will put more
load on drive motor so you'll have to recharge batteries more often.
Motor must press against left rear wheel with moderate tension;
a coil spring will do the job, run from one motor base hole back
to rear axle housing, or to spring shackle. Use as little tension
as possible, but get positive friction drive without slipping.
 If
steering motor turns wheels opposite to direction you move pulser
control knob, reverse connections to motor. If drive motor moves
car in reverse, shift built-in reversing switch on motor. A single
rubber band 1/8" wide, 3 1/2" long centered the steering servo.
Too much rubber won't permit sharp turns - too little will result
in a "wandering neutral". C&S pulser is ideal for this since
it has a trim control which allows you to set car for straight running,
with steering knob centered. Also, its pulse rate is high enough
so front wheels have very little wiggle. Our car travels a smooth
path, either straight or in turns of any radius.
While most would consider this a simple R/C installation, you
can add to it to obtain drive motor control, perhaps forward and
reverse, even change of speed, all on the same single channel radio
equipment. A "pulse omission detector" (POD) can be used directly
to start and stop the drive motor, or it could be linked to another
servo which will allow the more complex forward-stop-reverse action.
Car is large enough to take all this equipment under its hood, chassis
and rear deck so appearance won't be spoiled. We've given you a
basic racer - now let's see what more you can do with it!
Parts Required: ITC Mercer Raceabout kit; CG Saturn 3 volt super-regen
receiver; Citizen-Ship Actuator kit; Super-Monoperm electric drive
motor (GM Hobby Spec.); four Eveready N4OT nickel-cad cells (or
N52 - see text); two Eveready E93 C-size dry cells; Acme battery
holder; three SPST slide switches.
Also: Brass tubing, rod, cement, plywood, other small parts;
Babcock BCT-16 all-transistor tone transmitter; C&S Pulsi-Tran
proportional pulser; Eveready #246 9-volt battery for transmitter;
three Eveready pencells for pulser; one green plug for transmitter
(or 9-pin plug to make your own).
  This
advertisement for a 16" Motorized Giant Bobtail model car appeared
on a page adjacent to the article. It undoubtedly was meant to be
an enticement to modelers thinking about making the kind of R/C
conversion detailed in the article. Amazingly, you can still buy
that kit from Lindberg Products. According to the BLS's Inflation
Calculator, the $9.98 price in 1962 is the equivalent to $78.23
in 2014 money. The current Amazon price for the
Lindberg Bobtail is $75.28 - amazing!
Posted February 21, 2015
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