Re: Audio Tachometer for 2 stroke engine
- From: "Mook Johnson" <mook@xxxxxxxx>
- Date: Sun, 24 Apr 2005 18:55:16 GMT
The reason RPM is important is to make sure your setup the boat to run in
the RPM range where the engine has the most power. you can tell that from
the acceleration and jerk. Some guys get enginer builders to run their
engine on a dynomometer and get a HP vs RPM graph but never knwo what RPM
range their boat is running in.
The elite guys in this hobby are SERIOUS. They are trying to get every R of
performace out of the boats.
"Ross Herbert" <rherber1SPAMEX@xxxxxxxxxxxxxx> wrote in message
news:vptm611tfkuaud6p6jsgg7bsf3patld36f@xxxxxxxxxx
> On Fri, 22 Apr 2005 19:07:35 GMT, "Mook Johnson" <mook@xxxxxxxx>
> wrote:
>
>>I have a crazy idea to use a microphone near the exhaust of a 2 stroke
>>engine to measure the instantaneous RPM of the engine.
>>
>>The idea is non-contact RPM measurment in the presence is wind and road
>>noise. (lets say a motor bike running at high speed)
>>
>>For this application I'm interested in 10,000 to 40,000 RPM which is 166 -
>>666 Hz. If I acquire this signal and BP filter it then run it through a
>>FFT, do you guys think I can distinguish the (pop pop pop) frequency of
>>the
>>exhaust stroke from the noise?
>>
>>The high level requirements are
>>
>>a. non-contact RPM measurement
>>b. sensor must be waterproofable (is that a word? :))
>>c. must output a signal that can be acquired by a small microprocesor or
>>DSP
>>with A2D or Digital.
>>b. must be small relative to a 1.5" X 2.5" x .5" overall package
>>e. must be vibration tolerant (survivability and measurment accuracy)
>>f. At least several hour run time on a 2.8V, 800maH battery
>>g. Supply voltage is flexable but desired to be below 12V dc.
>>
>>
>
> I think the statement about "a crazy idea" in your first line sums up
> your proposal.
>
> For starters trying to accurately determine rpm at the update rate you
> require (100mS)using the "sound" from a small motor would require some
> serious signal processing which just couldn't be done with simple
> analog electronics IMO. The fact that all sorts of other noises would
> be present simultaneously would make the task akin to fishing an
> intelligent signal out of a spacecraft out past Jupiter using a 10W
> transmitter (not exactly but you get my drift).
>
> Quite frankly I can't really see why you need to know how many revs
> the motor on an R/C boat is doing anyway.You're still going to crank
> it up as much as possible if you are trying to catch up in a race and
> if it goes bang then it doesn't matter one hoot what the rpm's were at
> the time.
.
- References:
- Audio Tachometer for 2 stroke engine
- From: Mook Johnson
- Audio Tachometer for 2 stroke engine
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