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Message
Hi Thomas,
There at two design considerations that need attention
when designing a controller for an electric pitch prop. One is determining
prop rpm and the second is to determine when the pitch motor has reached its
limits of travel.
Prop RPM?
When I decided to design an electric prop automatic pitch
controller, I ran into the same design considerations. You need
engine/prop rpm from some source. I decided to use an IR sensor reading a
tape on the prop (to read its rpm directly) since I did not know what rpm
sources might exist on different automobile engine conversions as well as
different gear ratios which would ,of course, affect relationship between engine
and prop speed.
However, there are many ways to approach that need.
I currently derive RPM form my EFI Monitor from measuring the interval between
injections (once per e shaft rev). I suspect that Mark is taking a similar
approach to get rpm for his controller.
My controller was designed to maintain a certain prop rpm
by sensing the prop rpm and automatically varying the pitch to maintain that rpm
within a small window (to prevent rpm hunting). So if Power was increased
the prop would automatically increase pitch to absorb the power and keep the rpm
within the window and vice versa when power was reduced.
I also had three "pre-programmed" rpms for Take off, Climb
and Cruise that you could set by the push of a button. You could also
manual establish your target rpm.
I had the design 90% completed when the prop project went
away so never finished it.
Pitch Motor Limits?
I think the second problem, as you mentioned, is
determining the pitch motor travel limits to which I do not believe rpm is a
crucial factor. You could install limit switches with the risk of added
complexity and weight or you can devise a method to determine and warn
when the limits are approached.
I used a current sensing circuit (which you could
adjust for different current levels) to light an LED. The more current the
motor drew the brighter the LED glowed. So when the motor approached
its stall limit and current increased dramatically over the running current, the
LED would start to glow and the further you ran the motor to the limit the
brighter it would glow. The operator must take the corrective action -
although I already had a design in the conceptual stage to reverse the motor
when the current exceeded a set amount. Then I decided that I did not want
some computer making that decision {:>)
Hope this might clarify some of the
discussion
Ed
----- Original Message -----
Sent: Monday, January 23, 2006 9:46
AM
Subject: [FlyRotary] Re: Injector
pulseing ? Tracy ?
Question.
Why does he ( Mark B.) need the injector
pulses?
Unless he wants to have an automatic-best-performance
feature, a simple rpm reading from the crank will do fine.
a) Electronics will increase pitch when power is
increased to maintain rpm in C/S mode.
b) Pilot will change pitch in a variable pitch
mode.
AFAIU the problem is to find the exact endpoints of
pitch travel. How does knowing the injector pulse width help with
that?
It will tell him how much power is produced in
combination with an rpm input, but does he also measure airspeed?
Not bitching, just trying to get the idea!!
Thomas J.
Sent: Monday, January 23, 2006 8:55
AM
Subject: [FlyRotary] Re: Injector
pulseing ? Tracy ?
And how would Mark
Burton's constant speed controller
react if the EC2 was switched to injector
disable mode. Depending
on how it was wired, it might suddenly sense zero
power or 2X
power. Just thinking out loud.
Good point
Dean. If he only senses pulses to one injector, then it would have to
be the primary, which is always active, unless you turn it off via the
disable switch. He may not realize we have the ability to do
that, so it would be worth telling him about it.
Cheers,
Rusty
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