end stops. The speed of the servo movement can be
adjusted with the 100 ohm Cermet trimpot which is wired
in series with the receiver output to the gearbox.
An RF signal sent to the
receiver from its matching
transmitter will result in either a
positive or negative 4. 5 VDC
output, depending on which way
the transmitter key is pushed. This
will cause the gearbox to rotate
either clockwise or counterclockwise
which will also rotate the 10K pot.
The pot will then change the
controller pulse chain which will
signal the servo to move. The servo
will continue to move as long as the
transmitter key is pushed, until it
hits its endpoint.
Pushing the transmitter key in
the opposite direction will reverse all
of these actions and cause the
servo to move in the alternate
direction — again, until it hits its
endpoint. A small servo is shown in
Figure 2, but any sized servo can
be controlled depending on how
much 12V power is available.
Effective range with these
transmitter/receiver combos can
reach up to 75 feet.
The proper input voltage for
the receiver is 5 VDC. The servo
controller requires 12 VDC. You
could obtain the receiver voltage by
means of a +5V fixed voltage
regulator such as the NTE960, fed
from the 12 VDC supply (if it is
more convenient to use a single
The circuit diagram in Figure 1 shows
only one remote controlled servo, however,
most toy car transmitter/receiver pairs are
equipped with two separate output
channels. With a single receiver, you could
independently operate two servos by
adding a second gearbox/pot/controller setup which is
driven by the second receiver channel.
FIGURE 2. Top view of assembled wireless servo controller module showing receiver,
servo control board, and gearbox linked to potentiometer.
FIGURE 3. Remote controlled auto carrier with servo actuated
auto ramp tilt mechanism. Wireless controller module
is in gray car to the left of the auto carrier.
100 ohm Cermet trimpot
Microgear motor block ( 45 rpm)
10K linear 5/8" dia potentiometer
Hansen servo controller (kit)
3/8" dia shrink sleeving
Perforated phenolic board
*Removed from toy car
FIGURE 4. Rear view of
model steam shovel
showing servo location.
module is inside the
SERVO 08.2012 71