What began as a curiosity during a phone conversation with Louis Gabriel turned into a year-long collaborative design project. Some 6 months ago we produced the first flying copy of a solid state replacement for the solenoids that control the landing gear hydraulic pump. We thought we were done, but soon realized the Legacy community had an interest in the same sort of upgrade. Subsequently the switching capacity was doubled so that both the 235/320/360 and Legacy pumps could use the same controller.
Controlling the gear is a rather critical function. Not just from a reliability stand point, but also from the perspective of avoiding inadvertent activation. Safeguards were built in as a result.
The controller is a drop-in replacement, in that all the electrical connections that feed into and out of the solenoids are identical. Key differences difference is that the solid state controller requires much less current for switching. The intermittent solenoids require 2-3A and this limits the options with respect to pressure switches. Now any solid state pressure transducers can be used.
While the individual components on the board are not really being stressed, we still wanted to test well beyond the operational requirements. This included 10,000 cycles running for two weeks straight at higher current levels and longer cycle times than will be seen in use. Continuous on-times were also tested to simulate a failed pressure switch and run-away pump not noticed by the pilot.
RF picked up by all the up/down command lines is suppressed and grounded on the board. Trigger levels are set very high so that operating in a noisy RF environment will not affect operation. We even radiated 5W at a range of 1 inch just to be sure.
The typical switch bounce that comes off solenoids, and really any other mechanical switch, was eliminated by building in a 20ms delay at the input. This means the pump starts up only once instead of quick succession of start-stop-start-stop-start.
Another benefit is reduced weight. I lost 1.25 lb when I swapped solenoids for the controller.
Controllers are available for $295 (includes shipping)
If interested, contact Louis Gabriel or myself.