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From: Pete Sinclair <pete@leapfrogventures.com>
Subject: Dukes pressure controller
Thread-Topic: Dukes pressure controller
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Setting the maximum pressure to 5.5 psi:

The 1" brass cap on the outflow valve controls this.  The brass cap is unde=
r the lid to the left of the gears.  There is a set screw that needs to be =
loosened to turn the brass cap.  Clockwise should decrease the max pressure=
, counterclockwise should increase it.  In theory, it should not affect the=
 relationship between the pressure controller and the pressure head.

Calibrating the controller to the outflow valve:

Matching the controller to the pressure head requires realigning the gears =
to the right of the brass cap.  I would fly it to altitude, set the control=
ler to my desired altitude (with the rate knob at max rate).  Wait 5 minute=
s, then mark the position of the right most gear (on the potentiometer) whe=
re it is in contact with the small center gear (on the motor).  I would the=
n change the controller until I got the desired cabin altitude + 700 feet, =
and mark the position of the gear on the left (which controls the bellows w=
ithin the dukes pressure head) where it meets the center gear.  I would the=
n land and reposition the gears so that they were both facing the center ge=
ar at the marked position at the same time.  You may want to watch the rota=
tion of the gears as they change during flight to see if there is more than=
 one rotation required to reach the set point for both gears.  May take a f=
ew attempts to get right.=20

Note that the controller has no knowledge of the cabin pressure or actual a=
ltitude.  All it does is control a motor in the pressure head based on a po=
tentiometer position sensor.  It assumes the pressure head is set up to pro=
vide the proper response to the position set by the motor. =20

Eliminating the takeoff overpressure ear pop:

Pin 4 opens a solenoid in the pressure head that connects the vacuum port d=
irectly to the bellows.  This allows the vacuum to pull the bellows fully o=
pen (dump mode).  So, if you have vacuum, you want pin 4 grounded when on t=
he ground and taking off (to prevent the pop you get when going to full pow=
er).  I added a small electric vacuum pump to mine to do this that goes on =
whenever pin 4 is grounded.  Here is the source for it:

https://www.sparkfun.com/   $14.95 - ROB-10398 - Vacuum Pump - 12V =20