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 to
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]
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 (if any) are
Popular Electronics articles
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Here is my Bonner
3 and 4 Finger R/C Escapements
by E. L. Safford, Jr.
Although the one-arm escapement is capable of
allowing the R/C model air-plane 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, stabilizer, etc.
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 rotates.
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," "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.
A typical 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.
To simplify 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.
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
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 en-gages 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
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