This looks like a real simple way of using megasquirts on rotaries and
you have
redundancy. The engine will run on one rotor. It solves a lot of problems
using just
one Megasquirt on a rotary.
I has the advantage of using a notebook computer with a USB connector to
tune and
save injector tables to share with other people merely by emailing them.
Megatune is very sophisticated and easy to use tuning software that runs
on a notebook.
IMHO this is a great idea.
Paul Lamar
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Using MegaSquirt ‘out of the .box’
www.not2fast.com/megasquirt/doc/rotary_injection.doc
MegaSquirt introduction.
The MegaSquirt was design by Bruce Bowling and Al Grippo to be a simple
and cheap
batch fire fuel injection system. Been around for years.
There are 2 injector driver outputs on the MegaSquirt, running off the
PWM channels
of the MCU. This allows both saturated and peak and hold injectors to be
used on the
same hardware: very clever. This allows 2 different injection events to
occur in
parallel, which suits our purposes very nicely.
Specific needs of Rotary engines.
The rotary engine, due to the rotor layout has a few key differences with
a
reciprocating engine. Many of these work in our favor. And remember, the
otto cycle
is the otto cycle:
There are 2 rotors, spaced 180° apart. EFI.
Build 2 MegaSquirts.
Fit a pair of hall effect sensors one at 22 degrees BTDC and one 180°
later (top and
bottom) Hook one MegaSquirt to the top sensor and one to the bottom.
Burn in injector staging code if required.
Ignition.
The ignition pulse on 1 rotor corresponds to 22° BTDC on the inlet cycle
of the other
rotor, give or take the amount of advance being used. Very handy.
Use 2 MSD capacitor discharge units per rotor. One per plug. This is what
the racers
do and is it very simple and straight forward. Each Hall Effect sensor
fires two MSD
units 22 degree BTDC.
Injection.
Around 220-280° is available for injection. In a reciprocating engine, you
can ‘puddle’ fuel on the inlet port to increase the injection time. In a
rotary there
is little time for this before the next inlet cycle starts. This forces
relatively
large injectors to be used, with staged injection being a
useful method of getting high max flow rates and a good dynamic range.
For example,
at 8000 RPM 1 revolution is 7.5ms, giving around 6ms for injection.
In terms of injector strategies there are a couple in general use
The best for our use here is 2 injectors in each runner.
The code mods are very simple, if needed at all
You get the full 6 ms for injection at high RPM
2 MegaSquirts are needed so adding a full $100 to the costs
Tuning will be a little more tricky as you have to set each parameter
twice
----------------------------------------------------------------
I had an idea of using 3 megasquirts that fed a logic box that compares
the outputs
and forwards the one that at least 2 ms boxes agree on. Not sure if it's
really
feasible since that would induce some lag in the outputs.
Joshua
---------------------------------------------------------------------
SymTech Labs' coolant temperature sensor is a standard GM CLT sensor
capable of
interfacing with all MegaSquirt ECU's. It features 3/8" NPT threads and
can also be
used as an intake air temperature sensor (IAT/MAT). Each unit is shipped
with a 6"
pigtail for easy installation.
Intake Air Temp/Manifold Air Temp
The big question that I have is there seems to be conflicting info. Often
they talk
about a MAP sensor but this block diagram does not show it. A Manifold
Air Pressure
sensor (MAP) can be used to control the amount of fuel injected just like
an O2
sensor. That is what Tracy does.
Any type of feed back from an O2 sensor will not work as 100LL is death
to O2 sensors.
The MS flow chart shows a read of the MAP but the schematic shows no
connection to a
MAP sensor.
Can anybody help me out on this? Is the sensor on the mother board? Where
is it
connected?
BTW The megasquirt has the built in capability to send engine parameters
back to the
notebook in real time for use as an EFIS. The notebook software is
already available
to display these engine parms in real time. This is a real cheap EFIS.
Paul Lamar
Separate Megasquirts for each rotor is a great idea as long as there is no
danger of fire or explosion if the ignition for one rotor fails but the
fuel in-
jector continues, and unburned fuel air mixture continues out into the hot
rotary exhaust environment. Perhaps an electronic switch can be in-
corporated into the Megasquirt circuitry that allows the fuel injector to
fire
only after a recent ignition signal--"recent" as established from voltage
remaining in a capacitor which is otherwise charged from ignition
activity.
I am very interested in this one-megasq-per-rotor approach and would
appreciate if anyone has any ideas. Thanks.
Gene Kahn
-
Read the tunning manual.
http://www.megamanual.com/v22manual/mtune.htm
The complete manual is 14 megabytes. If anybody is interested I will
upload it to the
web site so you can download it from there.
It appears that one can connect the O2 sensor so the Megasquirt can auto
tune it
self. Then disconnect the O2 sensor if you have to burn 100LL. Then the
megsquirt
will continue to function properly on manifold pressure and RPM.
Somebody needs to get one and set it up on the bench to test it.
The stimulator (aka. stim) is a small board that supplies the signals to
MegaSquirt®
that would normally come from the engine to MegaSquirt® EFI Controller,
and display
the outputs from MegaSquirt® on a series of LEDs. This allows you to test
MegaSquirt®
EFI Controller, and learn the tuning software. It also helps you to
verify that
MegaSquirt® is operating correctly if you have problems on the vehicle,
and lets you
'play' with MegaSquirt® to better understand how it operates. Before
assembling your
MegaSquirt® EFI Controller, you should assemble the stimulator, which you
will use to
test your MegaSquirt® as you proceed.
http://www.megamanual.com/v22manual/v1stim.htm
The smallest, cheapest and simplest Megasquirt will work fine one per
rotor.
It is also much easier for me to modify the code as it uses 6800 asm and
the original
source code is available.
We don't need the ignition stuff if we use MSD.
Paul Lamar
Another thought from the peanut gallery...why not just use two complete
redundant
Megasquirt systems for each engine?
Gene Kahn
The original low cost, easy to reprogram MS was designed for a low RPM
piston
engines. The ignition feature flat did not work without certain kludges
for rotaries.
One could still say that. Using one per rotor means it has more time to do
what it is
supposed to do as it does not have to worry about when to inject fuel for
the second
rotor. It also gives it more time to send engine parms to the EFIS for
display and
logging. That feature alone makes it highly desirable. Something Tracy's
system can't do.
Paul Lamar
I have been emailing Megasquirt all day about the use of the system in the
Rotary powered aircraft. After his OMG disclaimer, he tells me that the
system will work- http://www.diyautotune.com/**tech_articles/how_to_**
megasquirt_your_mazda_fc_rx7.**htm<http://www.diyautotune.com/tech_articles/how_to_megasquirt_your_mazda_fc_rx7.htm
.
They have a display similar to Tracys, and the unit will send the data via
serial to a laptop. I have asked if the software is android compatible, and
so far no answer. I can always get a windoze tablet if I have to. Anyway,
he tells me that an A/B system is possible, but the additional boards are
needed for the rotary.
All together, without the display LCD, the cost was around 550.00, the
display is another 160.00
Not too bad for the entire system- to add a second ECM is another 300.00,
for a total of around $960 for a redundant, data logging, engine parameter
displaying, can program in flight EFI system.
The plan seems to be coming together- back to installing landing gear!
Kevin Alderman
There are several version Kevin. I don't think the early version known as Megasquirt
I or II cost that much. He is assuming you are going to use it for rotary ignition
and that is the real problem with Megasquirt. Boards must be added to do that. He
might be trying to sell you a later version.
He is also assuming a RX7 application and RX7's have sensors and controls we don't need.
Here is a parts list of Ver 2.2. Note the preprogrammed computer chip. All the parts
are really cheap with the exception of preprogrammed computer chip. That is probably
no longer available so they try to sell you a later version while jacking up the
price. Since that was designed years ago single chip computers became self
programming. It is called flash memory. Even new cars have self programing computer
chips.
In theory it is possible to use the old code on a new chip. I am looking into it.
If necessary I will design a new board specific for our use that uses the old
megasquirt code.
Paul Lamar
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