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By John Adams
Research and Development Manager
Horizon Hobby
Attention, giant scalers, jet jockeys and scale
builders. If you've ever dealt with the headaches of
synchronizing multiple servos that are connected to a
single surface, or if you've dreamed of having more
channels for that complex scale project, JR's MatchBox
is the perfect solution.
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Even pull-pull systems with servos mounted
inline can benefit from using the MatchBox,
insuring perfect servo synchronization.
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Servo Synchronizing Dilemma
Combining two or more servos to a single control
surface to provide the torque needed is common practice
with giant scale airplanes. At least two and as many as
four servos to actuate the rudder and two servos per
aileron is "standard operating procedure" for
33% and larger aerobatic models these days. The problem
is that the linkage geometry just never quite matches
throughout the full servo's stroke!
Ailerons are usually tapered causing geometry
differences at each control horn, plus it's nearly
impossible to exactly locate the control horn on the
hinge line. Differences in servo centering account for
another inaccuracy that commonly creeps into equation.
Rudders are even more finicky, especially when the
servos are mounted in the tail on opposite sides of the
fuselage. Add powerful digital servos that aggressively
maintain their position to the dilemma, and the need for
a perfect match gets even more critical.
JR's MatchBox to the rescue.
The MatchBox allows you to drive up to four different
servos from a single channel and to precisely adjust
each independently. Adjustments include:
Centering- Sub Trim
Travel Adjust- Allows independent adjustment in
each direction
Reversing- The direction of each servo can be
independently set
Reset- Returns all adjustmens to neutral
The MatchBox also allows the attached servos to be
powered by the flight pack battery (jumper installed) or
with an auxiliary battery (plugged in place of the
jumper). This spreads out the current consumption,
helpful when using many high-current draw servos and
avoiding running high current through the receiver,
single battery pack and wire harness.
Applications
While operating and synchronizing two to four servos
attached to a single control surface (like on a giant
scale rudder) was the primary reason the MatchBox was
developed, through testing we've discovered several
other unique uses.
Gyro- By hooking up a gyro between the MatchBox and
the receiver, all servos hooked to the MatchBox are
controlled by the gyro. This allows a gyro to be used in
airplanes with up to four rudder servos, on elevators
with up to four elevator servos, on ailerons with up to
four servos, or used to stabilize the rudder and nose
wheel steering servos simultaneously.
Adding channels- By using retract servos, it's
possible to add three additional non-proportional
channels. With JR's 10X, that makes 13 channels! By
offsetting the kick point and using three position
switches, it's possible to actuate individual retract
servos in series. For example, switch position 1 drops a
bomb, position 2 turns on landing lights, position 3
extends the speed brakes... jet and scale guy, eat your
heart out!
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