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Ed,
What a great idea, sorry it never made it to the general flying
public.
Ivo does, in fact have a C/S controller. Reading some posts, some are not
happy with it and have removed it, much like some are unhappy with rotaries and
have removed them, despite the success others are having.
The ivo controller has a simple hall effect transducer which reads a magnet
buried in one of the prop blades, or the spinner back plate, if a normal spinner
is used (as opposed to the skull-cap that IVO sells).
It does not use the amp draw of the blade change mechanism at all, to
the best of my knowledge. The draw will disconnect if the physical limits are
hit in the case of an error. The controller, electronically is set for max and
min pitch via it's adjustments.
Don't know about the circuitry or the programming-- haven't taken mine
apart--yet. When engaged, and properly adjusted (several pots) the RPm is
controlled by a knob, which obviously is a POT. there are switches (remotely
mounted) to select manual pitch change or C/S.
Rich
In a message dated 6/14/2012 11:29:59 A.M. Central Daylight Time,
eanderson@carolina.rr.com writes:
Back a few years ago, there was a variable pitch prop
hub designed by a genus of a mechanical engineer. It had a pitch control
mechanism similar to the IVO adjustable pitch prop. I designed a control
circuit which among other things monitored the current draw of the pitch
motor.
While the prop project was not completed (to the best of
my knowledge), I found it was possible by conducting some test
measurements to correlate the current draw curve to propeller pitch. Now
the missing part was - we never got to the point of installing and
running the prop using the controller. Its highly likely that the
current curve would be different under air loads than not. We did not
use a meter but instead had the current turn on an LED (red) when the limit
was hit.
One of the things that I had planned to do was
incorporate a manifold pressure input (as well as prop rpm) to automatically
adjust to prop pitch to maintain rpm under various loading. The hardware
to do so was completed and the software - just never got tested.
Just found some of the old code
begin //Main
RPM_Limit_Low :=
3000;
RPM_Limit_High:= 7000;
RPM_TO := 5800;
RPM_CC := 5600;
RPM_CR := 5200;
RPM_DC := 5500;
//Put address of varible RPM_TO into
Pointer variable
PORTB.RB0 := 1; //set to enter while
loop in procedure
While testbit(INTCON,RBIF) = 0 do
I now recall that we actually had several target
settings such as TO (Take off), CC (Cruise Climb), CR (Cruise Range), and
others for various flight regimes. So you could choose TO, CC, CR or DC
from a menu and the prop was pitch was positioned/adjusted to maintain the
rpm. Manifold pressure was also a factor. Also it had direction
LEDs so you could select to manuall/electrically increase or decrease pitch
and a bunch of other things I have now forgotten. You could adjust those
rpm values that best suited your particular aircraft/engine combination - the
preset values were intended to reduce the pilot work load.
I was programming a PIC 18F450 chip to handle the
control and sensor inputs and provide a user interface on an LCD display with
buttons.
It would have been great had the prop project gone on to
completion, but alas despite the best efforts of a number of good folks it did
not.
Ed
Sent: Wednesday, June 13, 2012 5:52 PM
Subject: [FlyRotary] Re: IVO Prop controls
I think there's a miscommunication about how this device works.
It's quite simple: two commutator brushes on a fixed arm transfer current into
the prop hub to engage the motor and twist the prop blades. Like most
motors/actuators, you wire it such that positive voltage is applied to turn it
one way, negative turns it the other, and while not moving there is no voltage
applied. A simple (ON)-OFF-(ON) switch drives this.
There are only two
brushes so there's no way to transfer an at-limit signal, and although I'm
just guessing here, a reliable pair of limit switches that can operate
properly inside the prop at full RPM would have been complicated/maybe
unreliable? They'd also be a pain to adjust.
Anyway, the motor draws
only a moderate amount of current in the middle of its travel, and this
increases as you approach the limits. Standard practice is to install a meter
to indicate this draw and it tells you when you're near the limit.
You
could install a PTC instead of a breaker, but it's hardly an emergency. It's
not actually SOP to run it that far - in the times I've flown with John I
don't recall him ever doing it except perhaps once to show me what happens.
You don't "run it until it pops." You "run it until it's where you want it to
be." So PTC or breaker, it doesn't really make that much of a difference.
Choose the safety device you prefer.
I don't understand the bit about
the shorted switch. That's pretty rare, and the breaker would deal with it
just fine. And I can't speak for anybody else, but every car I've ever owned
doesn't use a PTC to set the travel limit on the window, it uses a limit
switch on the actuator. I recall having to adjust mine one time in a Subaru,
just like the nose gear travel switches in a Cozy.
Besides, what's the
down side here? You short your switch and the breaker will deal with it, and
the prop will stop twisting. No matter WHICH device you use, in this case you
now have no way to move the prop because a short would hold a PTC open and
also keep tripping a breaker when you manually reset that. Both devices have
the same failure mode if it's the switch that's the problem. But you still
have a working prop even if it's not at the optimal pitch. See if you can
jiggle the switch to clear the short...
To each his
own.
Regards,
Chad
On 6/13/12 5:15 PM, Lehanover@aol.com wrote:
Why in the world would IVO use a device that is designed
to fail critical flight gear in the case of improper control
manipulation
when they don't have to? Isn't this the classical and proper application for
a polyfuse? Polyfuses are
used in power windows for this exact reason.
You're kids can pull on that switch all day without damaging the
window
motor. I'm thinking of the case where a switch gets shorted (like
my belt sander's switch is right now...the power cord
is serving as a
temp fix until I get time), or someone accidentally leans something against
the switch.
Why does the motor draw current after the pitch has been changed?
Lynn E. Hanover
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