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PICList Thread
'Timing Advance for RC engine'
1997\02\07@124339 by Don Harris

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Any of you have experience with timeing advance for a gasoline engine.  I
have
a hall affect pickup on the prop hub for a model airplane engine, and will
us this to trigger the appropriate delay for the spark. The pic will accecpt
the hall affect input and initiate the appropriate delay (based on RPM),
and then output a pulse to trigger a capacitive discharge ignition.  I have
designed the CD but need help with programming the pic (12cxx 8 pin). I
am an electronics tech but could probably modifiy code to suit my application
if there is an example out there.  Does not have to be for the 12cxx
chip.

Thanks in advance

Don Harris

1997\02\07@165943 by Craig Knotts

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Attachment converted: wonderlandfive:ATTACH01.TXT 2 (TEXT/CSOm) (0000B5E1)

1997\02\07@171653 by Peer Ouwehand

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At 16:55 97/02/07 -0500, you wrote:
>Attachment Converted: C:\.......\ATTACH01.TXT


Craig,

Could you please send your text comments in the body of the message....
Attachments are _usually_ used for binairy files....

Thanks in advance,
Peer.

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1997\02\07@184424 by Andrew Warren

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Don Harris asked:

> Any of you have experience with timeing advance for a gasoline
> engine.  I have a hall affect pickup on the prop hub for a model
> airplane engine, and will us this to trigger the appropriate delay
> for the spark. The pic will accecpt the hall affect input and
> initiate the appropriate delay (based on RPM), and then output a
> pulse to trigger a capacitive discharge ignition.  I have designed
> the CD but need help with programming the pic (12cxx 8 pin).

and Craig Knotts <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU> replied:

> Keep in mind that spark ignitors are wonderful noise generators,
> producing perhaps the most difficult envionment in which to get a
> microcontroller to run.

Let me add some software-specific comments to Craig's good advice:

Timing advance is a real tricky thing to get right on any engine
that doesn't run at a more-or-less constant speed.  I don't know
much about RC planes, but I suspect that their engines change speed
DRAMATICALLY in flight (they don't have adjustable-pitch props, do
they?).

You'll find, I think, that unless your code is very clever, the
timing will retard whenever the engine is accelerated.  On a tiny
model-plane engine that can presumably accelerate VERY rapidly, this
timing change could be quite substantial.

Of course, steady-state ignition timing should be no problem with a
PIC... Just be very careful with electrical-noise suppression in
your circuit, and make sure that you make allownaces in your code
for engine-start timing (which will necessarily be very different
from the timing you use at operating RPM).

-Andy

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1997\02\07@190255 by Tony Matthews

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Don Harris wrote:
>
> Any of you have experience with timeing advance for a gasoline engine.  I
> have
> a hall affect pickup on the prop hub for a model airplane engine, and will
> us this to trigger the appropriate delay for the spark. The pic will accecpt
> the hall affect input and initiate the appropriate delay (based on RPM),
> and then output a pulse to trigger a capacitive discharge ignition.  I have
> designed the CD but need help with programming the pic (12cxx 8 pin). I
> am an electronics tech but could probably modifiy code to suit my application
> if there is an example out there.  Does not have to be for the 12cxx
> chip.
>
> Thanks in advance
>
> Don Harris
I realize this not is responsive to your question however the subject
interest's me .Should you not allow for throttle up and temperature
variations as well as rpm? Just curious.Oh yeah and I assume it was the
magnet you mounted to the hub or have you a more subtle method.Lead me
Tony M.

1997\02\08@015104 by Walter Banks

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> Don Harris wrote:
>
> Any of you have experience with timeing advance for a gasoline
> engine.  I have a hall affect pickup on the prop hub for a
> model airplane engine, and will us this to trigger the
> appropriate delay for the spark. The pic will accecpt
> the hall affect input and initiate the appropriate delay
> (based on RPM), and then output a pulse to trigger a
> capacitive discharge ignition.  I have designed the CD
> but need help with programming the pic (12cxx 8 pin). I
> am an electronics tech but could probably modifiy code
> to suit my application  if there is an example out there.
> Does not have to be for the 12cxx chip.


Many years ago in my dim and dark past I worked on a
project with two friends to build an endurance RC plane.
We converted a glow engine for spark ignition. The pickup
we used was capacitive. We replaced the back
prop washer with a disk that had a hole filled with
epoxy that gave an abrupt change in the effective capacitance
between the disk and a non contact pickup. The ignition
system was a small CD system. The electronics took the
throttle servo control signal to control the spark
advance.

We spent a lot of time getting the electrical noise down
to reduce radio interference. In the end this was not a
problem so I suspect the processor would not be a problem.

If I had to do it again I think I would decode the throttle
signal with the processor and have the processor drive the
throttle servo. That way the processor can use the throttle
signal as a setpoint in a control system. The processor can
measure RPM, setpoint and control spark advance and throttle
position.

Walter Banks
http://www.bytecraft.com

PS The plane flew a little over 8 and half hours.

1997\02\11@020258 by Marv

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>Don Harris wrote:

>Any of you have experience with timeing advance for a gasoline engine.  I have
>a hall affect pickup on the prop hub for a model airplane engine, and will
>us this to trigger the appropriate delay for the spark. The pic will accecpt
>the hall affect input and initiate the appropriate delay (based on RPM),
>and then output a pulse to trigger a capacitive discharge ignition.  I have
>designed the CD but need help with programming the pic (12cxx 8 pin). I
>am an electronics tech but could probably modifiy code to suit my application
>if there is an example out there.  Does not have to be for the 12cxx
>chip.

 You probably should consider using one of the chips with an interrupt, if
you want to keep the timing accurate to a degree or so, at the 10,000+ RPM,
if I recall correctly, those little engines are spinning.

Marv

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