It's refreshing to see some things coming in worthy of being saved in the
"Worthy RCSE Posts" folder. Keep them coming!
----- Original Message -----
From: <[EMAIL PROTECTED]>
To: "Rob Davis" <[EMAIL PROTECTED]>
Cc: "Rob Davis" <[EMAIL PROTECTED]>; "Harley Michaelis"
<[EMAIL PROTECTED]>; <[email protected]>
Sent: Tuesday, August 15, 2006 10:07 AM
Subject: Re:[RCSE] Great Ideas
Not sure what you mean by fails open, I suspect you mean fails "closed".
The
Fromeco units do not rely on physical contact actuation to supply main
PWR, but
rather electronic means by transistor/FET. The flag/pin negate main
current
flow by holding the (electrical) junction open. When the pin is removed,
essentially current flows until either the system's (electronic switch in
this
case) current capabilities are exceeded or the pack/lead material dies.
On some HLG's folks employ miniature speaker phone jacks to make/break
contact
to supply PWR to the control system. In this example current flow is
relatively
low, so one can get away with it (most of the time).
On larger aircraft, where there is a definite spark as contact is made or
broken, carbon build-up (or even material transfer) occurs which makes the
area
of actual contact a hit-or-miss scenario. A cycle-up on one flight might
make
adequate contact...while on another it may only supply enough current to
move
the control surfaces while still on the ground. Once under load, like
during
launch, the contact area may fail...and down goes your pride and joy.
The slider switch normally used by pretty well everyone has a wiping
action as
contact is made and broken. It is this wiping action that not only ensures
adequately cleaned surfaces, but also adequate contact area to flow it's
rated
current specification.
This is precisely why employing rocker switches or phone jacks, with no
wiping
action, that gets folks into trouble...don't employ them if you value your
aircraft!!! There are significant electro-mechanical reasons they are not
used.
Quoting Rob Davis <[EMAIL PROTECTED]>:
To add to Simon's note. I normally build / buy my batteries with dual
leads.
One lead is used to charge and the other plugs into the switch.
Charging
through a switch is normally a bad idea.
I like the idea of a switch that fails open. I've used Fromeco's pin
flag
switches on other aircraft and wonder why I've not seen any saiplanes
using
them. The switch has a pin that you remove to turn on the aircraft. The
pin
(2-3 inches in length) normally has the proverbial "Remove before flight"
streamer attached to the pin requiring a 2-3mm hole in the canopy of fuse
to
allow the pin access to the switch. It ought to lead to fewer failures
to
turn on the plane prior to launch. But then again a quick control check
would
accomplish this task as well.
Rob
Simon Van Leeuwen
PnP Systems - The E-Harness of Choice
Radius Systems
Cogito Ergo Zoom
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