3 and 4 Finger R/C Escapements
January 1955 Popular Electronics
you're still using the "old" one-arm escapements in your radio controlled
model airplane, you're probably also still using that "greasy kid
stuff" in your hair as well. Just like the hip guy has switched
Vitalis, the hip modeler has switched to multi-arm escapements
that allow more than just full left/right or full up/down throw
on the rudder or elevator, respectively. Today's equivalent would
be advocating for the use of digital servos versus the "old" analog
servos. The more things change, the more they stay the same.
[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. As time permits, I will be glad to scan articles for
you. All copyrights (if any) are hereby acknowledged.
Here is my Bonner
3 and 4 Finger R/C Escapements
by E. L. Safford, Jr.
the one-arm escapement is capable of allowing the R/C model airplane
flier to execute a wide variety of maneuvers, more and more complex
escapements are being used. These provide a more flexible system
of control, allowing more intermediate positions for the rudder,
In order to describe the operation
of the more complex escapements, each extension will be referred
to as a finger; each finger is intercepted by catch points as it
The three-finger escapement is illustrated
in Fig. 1. Notice that the fingers are set 120 degrees apart, and
that the catch points of the relay armature are located exactly
the same as those on the one arm (or two- finger) escapement. The
solid lines represent the signal "off" positions. The dotted lines
represent the signal "on" positions.
To complete a 360-degree rotation of the crank, the following signal
sequence is necessary: "on-off," "on-off," "on-off." This compares
to the sequence for the two-finger escapement which is: "on-off,"
Fig. 1. Three finger R/C escapement furnishing three left positions,
two right positions, and one neutral crank position.
Fig. 2. A four finger escapement with three left and three right
positions, two neutrals. This of course allows for more flexible
control of a model airplane or boat by radio control.
Fig. 3. A four finger escapement. Fig. 2 shows its mode of operation
giving three left, three right. and two neutral positions.
Fig. 4. The Bonner compound escapement used for radio control.
Notice the ratchet wheel and rocker arm combination for smoothing
out the rotation and the spring contacts on the front view.
Why use this type of escapement? The reason
is more control. If the distance H is made equal to the distance
from the shaft to the crank, the deflection of the loop to the right
and left will be equal in positions C and G. These are the first
and third "on" positions respectively, and represent the maximum
deflection possible. Now notice that the loop will be deflected
in positions D and F, but not as much. These are the first and second
"off" positions. The B position is neutral; E is so slightly left
that it can be used as a neutral.
Thus, with this
type of escapement, it is possible to have two positions to the
right and three to the left and also a single neutral. In steering
applications a rudder may be placed in the "half" positions and
allowed to remain there as long as desired without consuming power.
One can also have full deflection in either direction, but only
while the push-button is depressed. This is desirable particularly
in planes where sharp turns do not want to be sustained.
four-finger escapement is shown in Figs. 2 and 3. This type is popular
for boat steering. The catch points of this escapement move the
arms in 45-degree jumps instead of the 90 degrees of previous types.
This type of escapement will provide three positions left or right,
as shown in Fig. 2.
To remember just how many times to push
the button to get a particular deflection will be a problem. It
is possible, however, to design a ground control unit which will
send forth the correct sequence for the position desired merely
by moving a steering lever or wheel to the left or right.
the ground control unit and yet allow particular signals to be transmitted
for left and right (and one other function), the Bonner compound
escapement was developed. (See Fig. 4.)
The sequence of
signals is simple and can be readily performed with a push-button.
Pushing the button once will give "left." Holding the button down
will prolong this position. To obtain "right," push the button down;
release, and down again. Hold it down as long as you desire "right."
For the third function, the sequence is "on-off," "on-off," "on."
If one sends two quick pulses for "right" and desires to repeat
"right," he just sends the same two pulses as before. The same applies
to "left," or to the third function. This is possible because the
escapement is designed with only one neutral or starting position.
It returns to this neutral automatically whenever the signal remains
off for any length of time. Other escapements can be made to do
this, but require that a "neutral" command be transmitted after
the steering command ends.
How does the Bonner compound
work? Refer to Fig. 4. Notice that the fingers are not symmetrically
spaced. This is done to allow the crank to be positioned left or
right by the "on" catch point only. Notice also that the finger
to which the crank is attached is offset. The "off" armature catch
point is also offset to intercept it alone. Thus, in the signal
"off" position, this finger is intercepted by the armature catch
point and this corresponds to the neutral steering position.
Assume that the escapement has a rubber-band attached and is ready
to operate. Refer to Fig. 5. If a signal is transmitted, armature
Y pulls down releasing the offset finger. At the same instant, the
"on" catch point moves in and finger 3 is intercepted and held.
This is "right." If now, the signal is turned off, this catch point
moves back, releases finger 3, and the shaft rotates clear around
until the offset finger (1) again engages armature Y. The steering
element has returned to neutral.
Notice the front
of the escapement with its ratchet wheel and rocker arm that engages
the teeth on the ratchet wheel (Fig. 4). This prevents the escapement
shaft from snapping from one position to another. It causes the
fingers to move around at a definite speed.
Fig. 5. Diagram of the Bonner compound escapement
in the neutral position.
For example, to obtain "left,"
a signal is sent causing armature Y to pull down. Finger 3 is intercepted
by the "on" catch point. Now, assume the signal is broken for just
an instant and transmitted again. The rocker prevents the shaft
from snapping around and so, the "on" catch point which moved back
when the signal was broken,. now moves forward again before finger
4 can get by. While the catch point holds finger 4, the crank is
"left." If the signal is turned off momentarily and on again, the
offset finger slips by, but finger 2 is caught and held. The crank
is almost at neutral and there is no steering, but another part
of the escapement now enters the picture to do another job.
Right behind the ratchet wheel is located a set of spring contacts
which are now closed by a tiny nub on the bottom of the wheel. This
can close a circuit to operate the extra function, which can take
the form of a motor speed control, reversing control, gas feed control,
etc., depending on the type of model controlled.
Posted October 19, 2011