Received-SPF: pass
 receiver=logan.com; client-ip=72.52.218.78; envelope-from=bob@bob-white.com
Date: Mon, 11 May 2009 12:22:59 -0600
From: Bob White <bob@bob-white.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Pulses Per Rev and the TACH: [FlyRotary] Re:
 John Downings Tach
Message-Id: <20090511122259.2f832d32.bob@bob-white.com>
In-Reply-To: <list-3638683@logan.com>
References: <list-3638683@logan.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit

Thanks Jeff,

A call to UMA turned out to be the simplest solution.  They gave me a
part number for a special order that would trigger on the coil 5V
trigger signal and scale correctly to 1 pulse per rev.

I would like to thank everyone who helped with this.

Bob W.

On Mon, 11 May 2009 09:45:04 -0700
Jeff Whaley <jwhaley@datacast.com> wrote:

> Hi Bob, Ed, sorry for the late reply but this is my work email, so I'm not active on the list during weekends.
> I'm on my lunch hour ... anyway, yes the 2 pulses per 720 degrees is correct and not 2 pulses per 360; the rest of my explanation about the UMA was correct. It will not work properly with 2 spark plug pick-ups on a 6-cyl but it should work just fine if connected to the Leading plugs of each rotor on the rotary. The digital UMA conditions the spark plug pulses then drives a 555 timer circuit creating a much more uniform pulse train, the pulse train is then sent to a frequency-to-voltage convertor. So for a 4/4 or a 2/2 the f-to-v convertor should see 2 equally spaced pulses every 720 degrees but if tapping 2:6 cylinders the spacing will no longer be uniform which translates to a lower frequency, a lower voltage and a display error.
> Jeff
> 
> -----Original Message-----
> From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Bob White
> Sent: Friday, May 08, 2009 7:00 PM
> To: Rotary motors in aircraft
> Subject: [FlyRotary] Re: Pulses Per Rev and the TACH: [FlyRotary] Re: John Downings Tach
> 
> Hi Ed,
> 
> "if you are just
> tapping one spark plug you would get 1 spark per 360 deg."
> 
> I'm not quite convinced of that.  Every piston fires once every 720
> deg.  Compression/(fire plug)/power stroke is 360, then
> exhaust/intake is a second 360.   If I sample one plug I will see one
> spark for 720.  From Jeff's explanation, the tach mentioned samples
> two spark plug wires for a 4 cylinder 4 stroke (although I think this
> is 1 pulse per 360 rather than 2).  For a two stroke, only one plug is
> sampled, so still 1 pulse per 360.  At least I think that's what I
> understood Jeff to be saying.   On a 4/4 engine, the tach's that work
> with a coil and distributor will see two pulses per 360 as two
> cylinders will fire in one 360 and the other two in the next 360.
> 
> If I still have this wrong, then I need more help! :)
> 
> Bob W.
> 
> On Fri, 8 May 2009 16:32:20 -0400
> "Ed Anderson" <eanderson@carolina.rr.com> wrote:
> 
> > Hi Bob,
> > 
> > A four cylinder four stroke fires all four cylinders in 720 deg or two
> > cylinders each 360 deg (as you know).  Therefore, normally if you are just
> > tapping one spark plug you would get 1 spark per 360 deg.  However, most
> > (but not all)  tachs expect two pulses per 360 deg (frequently referred to
> > as 2 PPR (pulses per revolution -360 deg).  So if your tach is expecting two
> > per rev and is only getting one pulse per rev, then the period between
> > pulses is twice as long as what it is expecting and therefore it will
> > generally indicate 1/2 of the actually rpm (if its only get one pulse per
> > rev and is set up for 2 PPR).  Now on some tachs you can set the PPR from 1
> > to a large number, but for most of the ones we use its generally 2, 3 or 4
> > for 4, 6 and 8 cylinder engines.
> > 
> > A two stroke two cylinder fires both cylinders each 360 deg instead of 720
> > of the four stroke - therefore you get 2 PPR for the two cylinder two stroke
> > exactly like you get for 4 cylinders on the four stroke for 360 deg.  So a 2
> > cylinder 2 stroke and a 4 cylinder 4 stroke will read the same RPM.  At
> > least that is how I recall it works.
> > 
> > Ed
> > 
> > Ed Anderson
> > 
> > Rv-6A N494BW Rotary Powered
> > 
> > Matthews, NC
> > 
> > eanderson@carolina.rr.com
> > 
> > http://www.andersonee.com
> > 
> > http://www.dmack.net/mazda/index.html
> > 
> > http://www.flyrotary.com/
> > 
> > http://members.cox.net/rogersda/rotary/configs.htm#N494BW
> > 
> > http://www.rotaryaviation.com/Rotorhead%20Truth.htm
> > 
> > -----Original Message-----
> > From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
> > Behalf Of Bob White
> > Sent: Friday, May 08, 2009 12:18 PM
> > To: Rotary motors in aircraft
> > Subject: [FlyRotary] Re: John Downings Tach
> > 
> > Hi Jeff,
> > 
> > Thanks for the tip.  There is something I don't understand about the
> > specs for this unit.  It's good for 4 cylinder 4 stroke or 2 cylinder 2
> > stroke.  If I use the spark plug wire for the pickup, a 4 stroke
> > (piston) engine will see one spark per two rev.  Why does it matter how
> > many pistons there are?  If it's a wasted spark system, then one spark
> > per rev. just like a two stroke piston engine.  There must be something
> > basic I don't understand.  What sort of mod did it need for the V6?
> > 
> > BTW, what is the maximum rpm reading for that unit?
> > 
> > Thanks,
> > Bob W.
> > 
> > On Fri, 8 May 2009 07:48:47 -0700
> > Jeff Whaley <jwhaley@datacast.com> wrote:
> > 
> > > I like the belt and suspenders!!
> > > I am using a UMA digital tachometer 2 1/4" from Aircraft Spruce that was
> > originally designed for 4 cylinder engines using an electrical impulse
> > pickup from spark plug leads. I modified it to mate with the Ford V6; I have
> > modified it again to connect to the EC2 driving the R1 PRI injector. The
> > rotary firing system is similar to a 4 cylinder so if this tach is still
> > available (Part # 10-24885) it would work off spark plug impulse couplers.
> > > Jeff
> > > 
> > > -----Original Message-----
> > > From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
> > Behalf Of Bob White
> > > Sent: Friday, May 08, 2009 12:14 AM
> > > To: Rotary motors in aircraft
> > > Subject: [FlyRotary] John Downings Tach
> > > 
> > > John is using a standard tach that is normally connected to a
> > distributor/coil ignition system.  The straight 12V pulse used for the
> > > LS1 coils wouldn't activate it.  I built an interface for him that
> > involved taking that pulse as an input and generating a shorter constant
> > pulse width output.  I modified the tach to trigger on the lower voltage
> > signal, and adjusted the scale factor to read correctly with one pulse/rev.
> > As John reported, it worked for about 0.8 hours, then quit.  He is sending
> > everything back to me so that I can find out where the problem is.  I would
> > like to find a tach solution that John can use without modifying anything.
> > The parameters are he has a 2 1/16 inch mounting hole, the tach needs to
> > read correctly with 1 pulse/rev (would be the same as a two cylinder piston
> > engine with coil and distributor), should trigger directly on a 12V pulse.
> > > 
> > > I've found tachs on the web that mention working with distributorless or
> > electronic systems, but none of them were the 2 1/16 inch type.  I found a
> > converter, the MSD 8913, but on the Summit Racing catalog it specifically
> > says it won't work with the LS-1 system.  It work by sensing the current
> > pulses to the 12V power lead on the coil.  I don't know why it wouldn't work
> > with an LS-1 coil, but it doesn't seem like a good investment when the LS-1
> > is specifically mentioned as not working.
> > > 
> > > Can anyone recommend a tach solution that John can use with his LS-1 Coil
> > rotary engine combination?
> > > 
> > > On another topic, John has the only system I've heard of that has the
> > capability to run on either EFI or a carburettor.  John posted a picture of
> > his Tailwind a few days ago.  It's a very good picture but considering the
> > redundancy of the EFI/carb system, I felt that the picture was lacking.  I
> > submit this edited version as being more indicative of John's desire for
> > uncompromised safety.
> > > 
> > > Bob W.
> > > 
> > > --
> > > N93BD - Rotary Powered BD-4 - http://www.bob-white.com
> > > 3.8 Hours Total Time and holding
> > > Cables for your rotary installation - http://roblinstores.com/
> > > 
> > > --
> > > Homepage:  http://www.flyrotary.com/
> > > Archive and UnSub:
> > http://mail.lancaironline.net:81/lists/flyrotary/List.html
> > 
> > 
> 
> 


-- 
N93BD - Rotary Powered BD-4 - http://www.bob-white.com
3.8 Hours Total Time and holding
Cables for your rotary installation - http://roblinstores.com/