JR Lithium Battery Replacement

The MAT AirTrax has split elevators with no interconnecting linkage between the halves. Smaller models may use a forked push rod or tie the elevator halves together with a torque rod and use only one servo. For this IMAA legal plane, dual servos would be the best choice. This will give ample torque for control, but synchronizing the two servos to keep the elevator halves in alignment can be a problem. The elevator halves must move in the same direction at exactly the same rate, or adverse control situations will occur.

---

	The two servos were mounted to the sides of the fuselage below the horizontal stabilizer. The servos are connected to the receiver using a noise trap/amplifier extension cable with a Y-connector at the end.
The two servos now move at the same time, but not in the same direction. To keep the elevator halves moving in the same direction, the pushrod has to be on opposite sides of the servo. This would cause a difference in positioning of the elevator halves because of the different angles between the servo arm and the control surface horn. To keep the geometery of the linkages the same, one of the two servos had to be reversed. This way, both push rods will be parallel to each other and a straight line push rod can be used to each of the elevator halves. To reverse the servos rotational direction, the internal wiring in the servo must be changed. If you have soldering skills, the job is fairly straight forward.
	In this photo, the servo case has been opened by removing the four screws located at each corner of the servo. The servo shown is a RCD HS605BB with reasonably good speed, high torque and reasonable reposition accuracy, especially at 6 volts. Two wires connected to the motor and two wires connected to the potentiometer will have to unsoldered from the SMT (Surface Mount Technology) circuit board and resoldered.
On the HS605BB from RCD, the motor wires were orange and brown. Both wires were unsoldered and then resoldered in the opposite wire's location. The potentiometer wires were green and red. Again, these wires were unsoldered and then resoldered in the opposite wire's location on the SMT circuit board. Next the servo was reassembled and checked for proper operation. The two servos (one reversed by resoldering) worked together perfectly. A separate channel for each servo could also be used, if you are using a programmable radio with one free analog channel still available on the receiver. A separate electronic servo reverser could have been purchased also. The soldering changes took less than 5 minutes and cost very little (solder and time).
	Here is a normally wired HS85 servo. We needed to reverse it's travel, so we will save the money for servo reversers and just use a little time and resolder the motor and pot leads.
	Here the motor and pot wires have been unsoldered and resoldered. The two motor wires are reversed and the two outer wires on the pot have been switched. The modification is really simple and took 5 minutes (the iron takes three minutes to warm up).

 Builder's Corner

 Barnyard Buzzards Home Page