The Megasquirt was initially rejected for aircraft use as there
was no
method of
manually leaning it. The other problem was the Megasquirt relies
on the O2
sensor to
set the mixture. O2 sensors are damaged by 100LL. A third problem
was the
throttle
position sensor TPS was required.
As I recall Tracy used these problems years ago as the rational
for doing
his super
simple system that uses only manifold air temperature MAT/IAT and
manifold
air
pressure MAP to set the mixture at any RPM. Therein lies part of the
problem tuning
Tracy's system. Some people have taken a year of flying to get it
right.
The last thing was the Megasquirt rotary engine ignition problem.
The
rotary engine
ignition problem could be solved using extra hard ware and was
solved but
it was a
messy kludge.
I agreed with him at the time. That was years (10) before I had
the idea
of using one
cheap Megasquirt per rotor. One per rotor is likely to eventually
simply
solve the
ignition problem using off the shelf computer trigger inductive
coils like
the LS1
and the RX8 coils with out using one CD system per plug. One CD
system per
plug is
more expensive than a computer triggered inductive coil like the
LS1 or
RX8.
I know Motorola/FreeScale 68K asm code so in theory I can fix these
problems by
recoding the chip.
Another way of leaning the Megasquirt is trick the MS computer by
manually
adjusting
the O2 sensor input voltages and simulating the TPS as wide open
with
voltage
dividing potentiometers.
Perry Mick does something like that using a stock RX7 computer and
probably has over
1000 hours on it.
The siren song of the Megasquirt was and still is the built in
simple
EFIS, easy
tuning using a note book computer and data logging.
Time and new technology and new ideas tend to change old rational.
Paul Lamar
I've thought about the leaning problem with MS for the past
couple years
since the issue has come up. Seems you could leave out the O2
sensor and
replace it with a pot after the running parameters have been
programmed.
Then read your egt for best mix.
Seems we could also modify the injector dwell time similarly.
I have a
couple MS2 boxes and will loan you one if you like. I'm all
for using two
crank triggers, optical, hall, or whatever for a CD setup.
Ed Carver
Yes! I would like to test them Ed. I can come over and pick
them up.
Paul Lamar
Any time I guess, give me a heads up the night before.
Ed Carver
OK Ed.
Paul Lamar
Hi Paul,
I have been using two MS systems on a 4 cyl
opposed engine for some time, am about to test on a dyno. I run
the two
MS with two complete system sensors,ie., TPS, IAT,CYL temp, MAP,
seperate fuel pumps ect.,with RPM triggered from two separate
sensors. I
was running using the original ignition system, but one failed so I
upgraded the MS board with a daughter board which enabled me to
control
ignition timing, which for me involved relearning how to control the
ignition advance.
The two systems run on the same injectors, two leds on
the dash tell me if both are triggering the injectors,(you can
switch
either system off using either the ignition trigger or the power
to the
MS system without affecting the running of the engine), BUT, I
have not
figured out why when you switch either MS system back on with what
you
had switched off the motor runns like SH--t, until you turn off the
system again that you had originally switched off!!
I think it is
something to do with MS on switch on looking at the MAP sensor and
maybe
not being able to get a steady voltage from the ignition sensor?? I
reasoned that as the systems were switching the earth on the
injectors
that the left hand would not know what the right hand was doing,
and it
seems to be the case, except when one switches off one system!!! I
have
used the O2 sensor to program the fuel mixture, the thinking was
that
I would remove the O2 sensor after programming. I must be missing
something with what people are saying about leaning in flight,
surely
that if you have a system that adjusts mixture for altitude, and
load why
would you want to fiddle in flight, after programming the mixture
to be
progressively richer at higher and higher manifold pressures, and/
or RPM??
If starting again I would buy the later system with the ignition
controller built in, even if I was not using the ignition part of
the
system, the systems are so well assembled (when bought fully
assembled)
I do not think it is worth the bother to assemble oneself. MS
does not
rely on the O2 sensor to set the mixture, that is set with the VE
tables, you can of course use the Megatune to autotune using the O2
sensor, but i do not know that I would trust it to tune the range of
power/manifold pressures in aircraft in flight.
John Burey
It is one thing to maintain stoichiometric mixture with changes in
altitude and quite
another to lean. Leaning an engine will improve the BSFC at any
altitude and also
at the
expense of power. Most car engines will maintain stoichiometric at
all times.
This is a fundamental difference with aircraft engines. Every
licensed pilot is
taught this.
My implementation of two MS systems on a rotary are entirely
independent.
The rotor one system never tries to control rotor two and vice
versa.
Paul Lamar
-
John,
Thanks for relating that experience! But even if your injector
was steady on
as long as the plug was still firing, there was still combustion
taking place in
the combustion chamber instead of the exhaust system unless the
resultant
mixture was just too rich to combust properly...dont know...
Gene Kahn
Hi Gene,
I guess I forgot to say I have 2 spark plugs per
cylinder, so the seperate systems are completly seperate (except for
the
injectors), I, when changing the mixture tables, and ignition
tables, do
it on one MS system, save then download to the other system keeping
them
both the same, (timing and mixture). Then restart the engine on both
systems. There should be a difference when running one spark plug and
one system but there seems not to be a difference, I guess I will
notice
it when running on the dyno.
John Burey
Since both MS systems are in parallel on the injector lines, you
should
have an isolation diode in each injector wire from the MS to the
injector. Without it, voltage may be backfed into the MS system thru
the
injector output circuitry, possibly causing the processor to arrive at
an undetermined state. This could account for the improper operation
when power to the MS is restored, as it may bypass the power-on reset.
Victor Roberts
John, Victor, Paul and all...thanks for your help! I would be
interested
in adding a second independent leading plug to each rotary
combustion chamber since we dare not depend on just a trailing plug
[see prior thread on red hot exhaust systems!], and I appreciate
Victor's
circuitry planning for failure mode for 2 plugs. Mazda's LeMans engine
had 2 lead plugs per rotor [plus the trailing plug for 3 total per
rotor]...
but I am guessing they used a different rotor housing casting. The
second leading plug might be positioned close enough to the first one
[perhaps near the leading plug, and between the leading and trailing
plug, giving three plugs total per chamber], that the flame front still
works with the existing rotor face design. I will investigate this
with an
old rotor housing. If I am barking up the wrong tree someone can feel
free to set me straight. Meanwhile, I will take a close look at my
housing to inspect the coolant passages, and then make a slice or
two through the housing to get a better look at what metal might be
available for another plug etc.
I am also planning on being at Mazdatrix on Monday morning August
20th and will ask them about this and other things. If anyone has
anything else specific they would like me to ask, please let me know.
Gene Kahn
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