Does anyone know of a sensor that determines position, feeds back a
 signal
 to both allow position and preselection of motion? I am trying to
 fabricate
 a flap handle that when put in a position (say 30 deg flaps)
 actuates the
 motor; the sensor senses when the motor (flap) is there and then
 shuts off.
 Seems to me cowl flap linear actuators might do that? But I already
 have a
 motor and a way to sense flap position. I just need to feed it back
 and
 control it at the flap handle.
 Marc

 Any potentiometer will work as a sensor.
 http://parts.digikey.com/1/parts-kws/a-250k-potentiometer

 Paul Lamar

 Out put stage attached. The word I was looking for was voltage
 divider for the flap position selector switch. You will need a pot
 with as many turns as ball screw shaft (or proportional gearing).
 C. Smith


Paul,

Here is a decidedly simple and low-tech way to accomplish it:  let
us define
a "knife" type switch as consisting of female "contacts" and a male
"blade"
which closes an electrical circuit when the blade slides between the
con-
tacts.  The blade is directly attached to the flap position indicator,
visible through a slot on the panel.  Two sets of contacts are
attached to
the flap actuator handle...one set above, and another set below,
with a gap
in bet- ween.  When the flap actuator handle is moved, it engages
the blade
and the flaps move until the blade reaches the end of the contacts
and then
stops.  The upper set of contacts make the flap go down, the lower
set makes
the flap go up.  If you don't want to route the actual flap motor
current
through the panel, you can use relays.  I am not sure how this
device will
function when the blade is exactly at the end of the contacts,
whether there
will be intermittent contact, sparking etc.  but I am sure there are
many
ways to deal with these issues.  For example, you could spring-load the
blade so that once it reaches the end of travel, it will tend to
self-release even further.  Hope this idea spurs us on to much
better ones.

Gene Kahn



Marc,Just a thought but stepper motors are everywhere.  Your hard
drive, DVD burner and car instruments for small ones.  The one on my HP
large format printer drags a full roll of paper with no bearings on the
arbor.  NEMA series machine tool steppers are fairly inexpensive and
could retract landing gear.  You need a stepper driver board and if it
is 4 axis you can do the flaps and all 3 trim axis with the same board.
There is free  CNC software and quite a few inexpensive retail versions
(Mach3) and all sorts of ball screws on e-bay. The 32mm ones on my
milling machine came from there and there are mineature ones listed.
Run the CNC code in manual and incremental steps with the perameters set
for the amount of motion per step.


Another system I have built uses small hydraulic cylinders with
LVDT  (linear variable displacement transformer) windings inside the
cylinder  rod and a wireing plug at the base end. I used parker hanifin
for the control board.  I had 15 stops to set saw blades on a saw mill
edge trimmer.  The board matches a potentiometer whose value corresponds
to the position for each location.  I used  a double deck selector
switch for a few of them (simple)  but mostly push buttons and mineature
relays which could be set from multiple operating positions by the
operator or by a computer and limit switches. One pot can be on the
console to give variable positioning for random locations or marked with
stop positions. The same board will work with an external probe and a
moving magnet ring if there is no hydraulic cylinder.


And still another approach is useing stacked  double ended
hydraulic cylinders.  The "disposable" type are light.Two would give
four positions. The downside is the valves are heavy, however cartridge
valves only weigh ounces. I used some complex ones on lumber sorters and
they were $32 each and ran forever. some were $18 without built in
relief valves. These prices  were for  -8 valves made by Sun  and stock
manifolds are reasonable from Damain.  A single tool drills the stepped
hole with all the "O" ring locations etc. so I drilled my own to mix and
match cartridges in  -6-8  and -12 sizes.

george grimes