By John Adams
Research and Development Manager
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.
Even pull-pull systems with servos mounted inline can benefit from using the MatchBox, insuring perfect servo synchronization.
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.
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!