Hi Folks,
After the misleading information here about underrated micro switches
and diodes in Woodcomp propellers, here is a way to establish the health
of both the switches and diodes against all failure modes, without
disassembling anything.
I do this test periodically (I found no reason to distrust these
components to justify a daily check), but you could even make this test
part of the standard startup checklist if you wish.
Note that I designed this test for Woodcomp props with feathering and
reversing options, but it probably also works on the basic Woodcomp
models. (Maybe someone with such a prop can confirm this?)
The props with feathering and reversing options have a more powerful
pitch motor and are probably easier to provoke to overrun the pitch,
which is an essential part of this test.
1) Switch on the electrical power, but do not start the engine. The
entire test is conducted with the engine switched off.
2) With the controller on manual or disabled, use the pitch control
switch to drive the prop all the way to the fully fine (or coarse)
setting. Keep the switch steadily engaged until the pitch won't change
any further. With no aerodynamic load, and no target RPM for the
controller, the pitch will change much faster than while flying and the
pitch will overshoot. This will open the micro-switches. Opening of the
micro-switches is indicated by an interruption of power and subsequent
stop of the pitch motor. (If the motor stops very abruptly and current
continues to flow, this will indicate that the pitch mechanism jammed
against the physical end stop and the micro-switches didn't open. In
this case your current-gauge will indicate that a lot of current
continues to flow and possibly the CB will pop. The following steps will
further confirm that this is not the case but the limiter switches
instead cut the power, as it should).
3) Now very briefly move the switch in the opposite direction. Just long
enough to give the pitch a very small kick.
4) Now move the switch in the same direction as in step 2. (this is the
opposite direction from step 3). The pitch motor should not run. If step
3 was short enough, the prop is still in the overshoot position, and the
micro-switch is still open. Hence the pitch will not change and you
don't hear the pitch motor running. This will confirm that the diode is
not open circuit (otherwise step 3 would have failed) and has not
shorted (otherwise step 4 would fail). Furthermore this will confirm
that the pitch mechanism didn't jam against the physical end stop,
because if this were the case, step 3 moved it away from the stop and
you would be able to jam it once again against the stop in step 4. If
the pitch motor doesn't run in step 4 after moving it slightly back in
step 3, it confirms that the micro-switch has opened and the motor
didn't halt just due to reaching the physical end stop.
5) Although not necessary, you can repeat step 3 and step 4 a few times
in succession. At some point after having kicked the pitch a few times
with step 3, the pitch will get into the normal operational area again,
the micro-switch will close, and the pitch motor will start to run in
step 4. You have now fully established that both the micro switch and
diode are working correctly.
6) Now repeat this test on the opposite pitch limit. This will confirm
that the other set of micro-switches and diodes are functional.
It looks like a complicated test, but once familiar with this procedure,
it only takes a few seconds: Hold the switch engaged until the motor
stops, repeatedly toggle the switch rapidly back and forth and note that
the pitch only changes in one direction, and after a few toggles the
pitch changes in both directions. Any failure will reveal itself because
the behaviour of the pitch motor during this procedure will change
visibly and audibly when a diode or micro-switch malfunctions in any way.
Hope this helps,
Frans
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